Visual basic net руководство

VB.Net — Overview

Visual Basic .NET (VB.NET) is an object-oriented computer programming language implemented on the .NET Framework. Although it is an evolution of classic Visual Basic language, it is not backwards-compatible with VB6, and any code written in the old version does not compile under VB.NET.

Like all other .NET languages, VB.NET has complete support for object-oriented concepts. Everything in VB.NET is an object, including all of the primitive types (Short, Integer, Long, String, Boolean, etc.) and user-defined types, events, and even assemblies. All objects inherits from the base class Object.

VB.NET is implemented by Microsoft’s .NET framework. Therefore, it has full access to all the libraries in the .Net Framework. It’s also possible to run VB.NET programs on Mono, the open-source alternative to .NET, not only under Windows, but even Linux or Mac OSX.

The following reasons make VB.Net a widely used professional language −

• Modern, general purpose.

• Object oriented.

• Component oriented.

• Easy to learn.

• Structured language.

• It produces efficient programs.

• It can be compiled on a variety of computer platforms.

• Part of .Net Framework.

Strong Programming Features VB.Net

VB.Net has numerous strong programming features that make it endearing to multitude of programmers worldwide. Let us mention some of these features −

• Boolean Conditions

• Automatic Garbage Collection

• Standard Library

• Assembly Versioning

• Properties and Events

• Delegates and Events Management

• Easy-to-use Generics

• Indexers

• Conditional Compilation

• Simple Multithreading

VB.Net — Environment Setup

In this chapter, we will discuss the tools available for creating VB.Net applications.

We have already mentioned that VB.Net is part of .Net framework and used for writing .Net applications. Therefore before discussing the available tools for running a VB.Net program, let us understand how VB.Net relates to the .Net framework.

The .Net Framework

The .Net framework is a revolutionary platform that helps you to write the following types of applications −

• Windows applications

• Web applications

• Web services

The .Net framework applications are multi-platform applications. The framework has been designed in such a way that it can be used from any of the following languages: Visual Basic, C#, C++, Jscript, and COBOL, etc.

All these languages can access the framework as well as communicate with each other.

The .Net framework consists of an enormous library of codes used by the client languages like VB.Net. These languages use object-oriented methodology.

Following are some of the components of the .Net framework −

• Common Language Runtime (CLR)

• The .Net Framework Class Library

• Common Language Specification

• Common Type System

• Metadata and Assemblies

• Windows Forms

• ASP.Net and ASP.Net AJAX

• ADO.Net

• Windows Workflow Foundation (WF)

• Windows Presentation Foundation

• Windows Communication Foundation (WCF)

• LINQ

For the jobs each of these components perform, please see ASP.Net — Introduction, and for details of each component, please consult Microsoft’s documentation.

Integrated Development Environment (IDE) For VB.Net

Microsoft provides the following development tools for VB.Net programming −

• Visual Studio 2010 (VS)

• Visual Basic 2010 Express (VBE)

• Visual Web Developer

The last two are free. Using these tools, you can write all kinds of VB.Net programs from simple command-line applications to more complex applications. Visual Basic Express and Visual Web Developer Express edition are trimmed down versions of Visual Studio and has the same look and feel. They retain most features of Visual Studio. In this tutorial, we have used Visual Basic 2010 Express and Visual Web Developer (for the web programming chapter).

You can download it from here. It gets automatically installed in your machine. Please note that you need an active internet connection for installing the express edition.

Writing VB.Net Programs on Linux or Mac OS

Although the.NET Framework runs on the Windows operating system, there are some alternative versions that work on other operating systems. Mono is an open-source version of the .NET Framework which includes a Visual Basic compiler and runs on several operating systems, including various flavors of Linux and Mac OS. The most recent version is VB 2012.

The stated purpose of Mono is not only to be able to run Microsoft .NET applications cross-platform, but also to bring better development tools to Linux developers. Mono can be run on many operating systems including Android, BSD, iOS, Linux, OS X, Windows, Solaris and UNIX.

VB.Net — Program Structure

Before we study basic building blocks of the VB.Net programming language, let us look a bare minimum VB.Net program structure so that we can take it as a reference in upcoming chapters.

VB.Net Hello World Example

A VB.Net program basically consists of the following parts −

• Namespace declaration

• A class or module

• One or more procedures

• Variables

• The Main procedure

• Statements & Expressions

• Comments

Let us look at a simple code that would print the words «Hello World» −

Imports System
Module Module1
   'This program will display Hello World 
   Sub Main()
      Console.WriteLine("Hello World")
      Console.ReadKey()
   End Sub
End Module

When the above code is compiled and executed, it produces the following result −

Hello, World!

Let us look various parts of the above program −

• The first line of the program Imports System is used to include the System namespace in the program.

• The next line has a Module declaration, the module Module1. VB.Net is completely object oriented, so every program must contain a module of a class that contains the data and procedures that your program uses.

• Classes or Modules generally would contain more than one procedure. Procedures contain the executable code, or in other words, they define the behavior of the class. A procedure could be any of the following −

  • Function

  • Sub

  • Operator

  • Get

  • Set

  • AddHandler

  • RemoveHandler

  • RaiseEvent

• The next line( ‘This program) will be ignored by the compiler and it has been put to add additional comments in the program.

• The next line defines the Main procedure, which is the entry point for all VB.Net programs. The Main procedure states what the module or class will do when executed.

• The Main procedure specifies its behavior with the statement

  Console.WriteLine(«Hello World») WriteLine is a method of the Console class defined in the System namespace. This statement causes the message «Hello, World!» to be displayed on the screen.

• The last line Console.ReadKey() is for the VS.NET Users. This will prevent the screen from running and closing quickly when the program is launched from Visual Studio .NET.

Compile & Execute VB.Net Program

If you are using Visual Studio.Net IDE, take the following steps −

• Start Visual Studio.

• On the menu bar, choose File → New → Project.

• Choose Visual Basic from templates

• Choose Console Application.

• Specify a name and location for your project using the Browse button, and then choose the OK button.

• The new project appears in Solution Explorer.

• Write code in the Code Editor.

• Click the Run button or the F5 key to run the project. A Command Prompt window appears that contains the line Hello World.

You can compile a VB.Net program by using the command line instead of the Visual Studio IDE −

• Open a text editor and add the above mentioned code.

• Save the file as helloworld.vb

• Open the command prompt tool and go to the directory where you saved the file.

• Type vbc helloworld.vb and press enter to compile your code.

• If there are no errors in your code the command prompt will take you to the next line and would generate helloworld.exe executable file.

• Next, type helloworld to execute your program.

• You will be able to see «Hello World» printed on the screen.

VB.Net — Basic Syntax

VB.Net is an object-oriented programming language. In Object-Oriented Programming methodology, a program consists of various objects that interact with each other by means of actions. The actions that an object may take are called methods. Objects of the same kind are said to have the same type or, more often, are said to be in the same class.

When we consider a VB.Net program, it can be defined as a collection of objects that communicate via invoking each other’s methods. Let us now briefly look into what do class, object, methods and instance variables mean.

• Object − Objects have states and behaviors. Example: A dog has states — color, name, breed as well as behaviors — wagging, barking, eating, etc. An object is an instance of a class.

• Class − A class can be defined as a template/blueprint that describes the behaviors/states that objects of its type support.

• Methods − A method is basically a behavior. A class can contain many methods. It is in methods where the logics are written, data is manipulated and all the actions are executed.

• Instance Variables − Each object has its unique set of instance variables. An object’s state is created by the values assigned to these instance variables.

A Rectangle Class in VB.Net

For example, let us consider a Rectangle object. It has attributes like length and width. Depending upon the design, it may need ways for accepting the values of these attributes, calculating area and displaying details.

Let us look at an implementation of a Rectangle class and discuss VB.Net basic syntax on the basis of our observations in it −

Imports System
Public Class Rectangle
   Private length As Double
   Private width As Double

   'Public methods
   Public Sub AcceptDetails()
      length = 4.5
      width = 3.5
   End Sub

   Public Function GetArea() As Double
      GetArea = length * width
   End Function
   Public Sub Display()
      Console.WriteLine("Length: {0}", length)
      Console.WriteLine("Width: {0}", width)
      Console.WriteLine("Area: {0}", GetArea())

   End Sub

   Shared Sub Main()
      Dim r As New Rectangle()
      r.Acceptdetails()
      r.Display()
      Console.ReadLine()
   End Sub
End Class

When the above code is compiled and executed, it produces the following result −

Length: 4.5
Width: 3.5
Area: 15.75

In previous chapter, we created a Visual Basic module that held the code. Sub Main indicates the entry point of VB.Net program. Here, we are using Class that contains both code and data. You use classes to create objects. For example, in the code, r is a Rectangle object.

An object is an instance of a class −

Dim r As New Rectangle()

A class may have members that can be accessible from outside class, if so specified. Data members are called fields and procedure members are called methods.

Shared methods or static methods can be invoked without creating an object of the class. Instance methods are invoked through an object of the class −

Shared Sub Main()
   Dim r As New Rectangle()
   r.Acceptdetails()
   r.Display()
   Console.ReadLine()
End Sub

Identifiers

An identifier is a name used to identify a class, variable, function, or any other user-defined item. The basic rules for naming classes in VB.Net are as follows −

• A name must begin with a letter that could be followed by a sequence of letters, digits (0 — 9) or underscore. The first character in an identifier cannot be a digit.

• It must not contain any embedded space or symbol like ? — +! @ # % ^ & * ( ) [ ] { } . ; : » ‘ / and . However, an underscore ( _ ) can be used.

• It should not be a reserved keyword.

VB.Net Keywords

The following table lists the VB.Net reserved keywords −

VB.Net — Data Types

Data types refer to an extensive system used for declaring variables or functions of different types. The type of a variable determines how much space it occupies in storage and how the bit pattern stored is interpreted.

Data Types Available in VB.Net

VB.Net provides a wide range of data types. The following table shows all the data types available −

Example

The following example demonstrates use of some of the types −

Module DataTypes
   Sub Main()
      Dim b As Byte
      Dim n As Integer
      Dim si As Single
      Dim d As Double
      Dim da As Date
      Dim c As Char
      Dim s As String
      Dim bl As Boolean
      
      b = 1
      n = 1234567
      si = 0.12345678901234566
      d = 0.12345678901234566
      da = Today
      c = "U"c
      s = "Me"
      
      If ScriptEngine = "VB" Then
         bl = True
      Else
         bl = False
      End If
      
      If bl Then
         'the oath taking
         Console.Write(c & " and," & s & vbCrLf)
         Console.WriteLine("declaring on the day of: {0}", da)
         Console.WriteLine("We will learn VB.Net seriously")
         Console.WriteLine("Lets see what happens to the floating point variables:")
         Console.WriteLine("The Single: {0}, The Double: {1}", si, d)
      End If
      Console.ReadKey()
   End Sub
End Module

When the above code is compiled and executed, it produces the following result −

U and, Me
declaring on the day of: 12/4/2012 12:00:00 PM
We will learn VB.Net seriously
Lets see what happens to the floating point variables:
The Single:0.1234568, The Double: 0.123456789012346

The Type Conversion Functions in VB.Net

VB.Net provides the following in-line type conversion functions −

Example

The following example demonstrates some of these functions −

Module DataTypes
   Sub Main()
      Dim n As Integer
      Dim da As Date
      Dim bl As Boolean = True
      n = 1234567
      da = Today
      
      Console.WriteLine(bl)
      Console.WriteLine(CSByte(bl))
      Console.WriteLine(CStr(bl))
      Console.WriteLine(CStr(da))
      Console.WriteLine(CChar(CChar(CStr(n))))
      Console.WriteLine(CChar(CStr(da)))
      Console.ReadKey()
   End Sub
End Module

When the above code is compiled and executed, it produces the following result −

True
-1
True
12/4/2012
1
1

VB.Net — Variables

A variable is nothing but a name given to a storage area that our programs can manipulate. Each variable in VB.Net has a specific type, which determines the size and layout of the variable’s memory; the range of values that can be stored within that memory; and the set of operations that can be applied to the variable.

We have already discussed various data types. The basic value types provided in VB.Net can be categorized as −

VB.Net also allows defining other value types of variable like Enum and reference types of variables like Class. We will discuss date types and Classes in subsequent chapters.

Variable Declaration in VB.Net

The Dim statement is used for variable declaration and storage allocation for one or more variables. The Dim statement is used at module, class, structure, procedure or block level.

Syntax for variable declaration in VB.Net is −

[ < attributelist > ] [ accessmodifier ] [[ Shared ] [ Shadows ] | [ Static ]]
[ ReadOnly ] Dim [ WithEvents ] variablelist

Where,

• attributelist is a list of attributes that apply to the variable. Optional.

• accessmodifier defines the access levels of the variables, it has values as — Public, Protected, Friend, Protected Friend and Private. Optional.

• Shared declares a shared variable, which is not associated with any specific instance of a class or structure, rather available to all the instances of the class or structure. Optional.

• Shadows indicate that the variable re-declares and hides an identically named element, or set of overloaded elements, in a base class. Optional.

• Static indicates that the variable will retain its value, even when the after termination of the procedure in which it is declared. Optional.

• ReadOnly means the variable can be read, but not written. Optional.

• WithEvents specifies that the variable is used to respond to events raised by the instance assigned to the variable. Optional.

• Variablelist provides the list of variables declared.

Each variable in the variable list has the following syntax and parts −

variablename[ ( [ boundslist ] ) ] [ As [ New ] datatype ] [ = initializer ]

Where,

• variablename − is the name of the variable

• boundslist − optional. It provides list of bounds of each dimension of an array variable.

• New − optional. It creates a new instance of the class when the Dim statement runs.

• datatype − Required if Option Strict is On. It specifies the data type of the variable.

• initializer − Optional if New is not specified. Expression that is evaluated and assigned to the variable when it is created.

Some valid variable declarations along with their definition are shown here −

Dim StudentID As Integer
Dim StudentName As String
Dim Salary As Double
Dim count1, count2 As Integer
Dim status As Boolean
Dim exitButton As New System.Windows.Forms.Button
Dim lastTime, nextTime As Date

Variable Initialization in VB.Net

Variables are initialized (assigned a value) with an equal sign followed by a constant expression. The general form of initialization is −

variable_name = value;

for example,

Dim pi As Double
pi = 3.14159

You can initialize a variable at the time of declaration as follows −

Dim StudentID As Integer = 100
Dim StudentName As String = "Bill Smith"

Example

Try the following example which makes use of various types of variables −

Module variablesNdataypes
   Sub Main()
      Dim a As Short
      Dim b As Integer
      Dim c As Double
      
      a = 10
      b = 20
      c = a + b
      Console.WriteLine("a = {0}, b = {1}, c = {2}", a, b, c)
      Console.ReadLine()
   End Sub
End Module

When the above code is compiled and executed, it produces the following result −

a = 10, b = 20, c = 30

Accepting Values from User

The Console class in the System namespace provides a function ReadLine for accepting input from the user and store it into a variable. For example,

Dim message As String
message = Console.ReadLine

The following example demonstrates it −

Module variablesNdataypes
   Sub Main()
      Dim message As String
      Console.Write("Enter message: ")
      message = Console.ReadLine
      Console.WriteLine()
      Console.WriteLine("Your Message: {0}", message)
      Console.ReadLine()
   End Sub
End Module

When the above code is compiled and executed, it produces the following result (assume the user inputs Hello World) −

Enter message: Hello World   
Your Message: Hello World

Lvalues and Rvalues

There are two kinds of expressions −

• lvalue − An expression that is an lvalue may appear as either the left-hand or right-hand side of an assignment.

• rvalue − An expression that is an rvalue may appear on the right- but not left-hand side of an assignment.

Variables are lvalues and so may appear on the left-hand side of an assignment. Numeric literals are rvalues and so may not be assigned and can not appear on the left-hand side. Following is a valid statement −

Dim g As Integer = 20

But following is not a valid statement and would generate compile-time error −

20 = g

VB.Net — Constants and Enumerations

The constants refer to fixed values that the program may not alter during its execution. These fixed values are also called literals.

Constants can be of any of the basic data types like an integer constant, a floating constant, a character constant, or a string literal. There are also enumeration constants as well.

The constants are treated just like regular variables except that their values cannot be modified after their definition.

An enumeration is a set of named integer constants.

Declaring Constants

In VB.Net, constants are declared using the Const statement. The Const statement is used at module, class, structure, procedure, or block level for use in place of literal values.

The syntax for the Const statement is −

[ < attributelist > ] [ accessmodifier ] [ Shadows ] 
Const constantlist

Where,

• attributelist − specifies the list of attributes applied to the constants; you can provide multiple attributes separated by commas. Optional.

• accessmodifier − specifies which code can access these constants. Optional. Values can be either of the: Public, Protected, Friend, Protected Friend, or Private.

• Shadows − this makes the constant hide a programming element of identical name in a base class. Optional.

• Constantlist − gives the list of names of constants declared. Required.

Where, each constant name has the following syntax and parts −

constantname [ As datatype ] = initializer

• constantname − specifies the name of the constant

• datatype − specifies the data type of the constant

• initializer − specifies the value assigned to the constant

For example,

'The following statements declare constants.'
Const maxval As Long = 4999
Public Const message As String = "HELLO" 
Private Const piValue As Double = 3.1415

Example

The following example demonstrates declaration and use of a constant value −

Module constantsNenum
   Sub Main()
      Const PI = 3.14149
      Dim radius, area As Single
      radius = 7
      area = PI * radius * radius
      Console.WriteLine("Area = " & Str(area))
      Console.ReadKey()
   End Sub
End Module

When the above code is compiled and executed, it produces the following result −

Area = 153.933

Print and Display Constants in VB.Net

VB.Net provides the following print and display constants −

Declaring Enumerations

An enumerated type is declared using the Enum statement. The Enum statement declares an enumeration and defines the values of its members. The Enum statement can be used at the module, class, structure, procedure, or block level.

The syntax for the Enum statement is as follows −

[ < attributelist > ] [ accessmodifier ]  [ Shadows ] 
Enum enumerationname [ As datatype ] 
   memberlist
End Enum

Where,

• attributelist − refers to the list of attributes applied to the variable. Optional.

• accessmodifier − specifies which code can access these enumerations. Optional. Values can be either of the: Public, Protected, Friend or Private.

• Shadows − this makes the enumeration hide a programming element of identical name in a base class. Optional.

• enumerationname − name of the enumeration. Required

• datatype − specifies the data type of the enumeration and all its members.

• memberlist − specifies the list of member constants being declared in this statement. Required.

Each member in the memberlist has the following syntax and parts:

[< attribute list >] member name [ = initializer ]

Where,

• name − specifies the name of the member. Required.

• initializer − value assigned to the enumeration member. Optional.

For example,

Enum Colors
   red = 1
   orange = 2
   yellow = 3
   green = 4
   azure = 5
   blue = 6
   violet = 7
End Enum

Example

The following example demonstrates declaration and use of the Enum variable Colors −

Module constantsNenum
   Enum Colors
      red = 1
      orange = 2
      yellow = 3
      green = 4
      azure = 5
      blue = 6
      violet = 7
   End Enum
   
   Sub Main()
      Console.WriteLine("The Color Red is : " & Colors.red)
      Console.WriteLine("The Color Yellow is : " & Colors.yellow)
      Console.WriteLine("The Color Blue is : " & Colors.blue)
      Console.WriteLine("The Color Green is : " & Colors.green)
      Console.ReadKey()
   End Sub
End Module

When the above code is compiled and executed, it produces the following result −

The Color Red is: 1
The Color Yellow is: 3
The Color Blue is: 6
The Color Green is: 4

VB.Net — Modifiers

The modifiers are keywords added with any programming element to give some especial emphasis on how the programming element will behave or will be accessed in the program.

For example, the access modifiers: Public, Private, Protected, Friend, Protected Friend, etc., indicate the access level of a programming element like a variable, constant, enumeration or a class.

List of Available Modifiers in VB.Net

The following table provides the complete list of VB.Net modifiers −

VB.Net — Statements

A statement is a complete instruction in Visual Basic programs. It may contain keywords, operators, variables, literal values, constants and expressions.

Statements could be categorized as −

• Declaration statements − these are the statements where you name a variable, constant, or procedure, and can also specify a data type.

• Executable statements − these are the statements, which initiate actions. These statements can call a method or function, loop or branch through blocks of code or assign values or expression to a variable or constant. In the last case, it is called an Assignment statement.

Declaration Statements

The declaration statements are used to name and define procedures, variables, properties, arrays, and constants. When you declare a programming element, you can also define its data type, access level, and scope.

The programming elements you may declare include variables, constants, enumerations, classes, structures, modules, interfaces, procedures, procedure parameters, function returns, external procedure references, operators, properties, events, and delegates.

Following are the declaration statements in VB.Net −

Dim number As Integer
Dim quantity As Integer = 100
Dim message As String = "Hello!"

Const maximum As Long = 1000
Const naturalLogBase As Object 
= CDec(2.7182818284)

Enum CoffeeMugSize
   Jumbo
   ExtraLarge
   Large
   Medium
   Small
End Enum 

Class Box
Public length As Double
Public breadth As Double   
Public height As Double
End Class

Structure Box
Public length As Double           
Public breadth As Double   
Public height As Double
End Structure

Public Module myModule
Sub Main()
Dim user As String = 
InputBox("What is your name?") 
MsgBox("User name is" & user)
End Sub 
End Module

Public Interface MyInterface
   Sub doSomething()
End Interface 

Function myFunction
(ByVal n As Integer) As Double 
   Return 5.87 * n
End Function

Sub mySub(ByVal s As String)
   Return
End Sub 

Declare Function getUserName
Lib "advapi32.dll" 
Alias "GetUserNameA" 
(
   ByVal lpBuffer As String, 
   ByRef nSize As Integer) As Integer 

Public Shared Operator +
(ByVal x As obj, ByVal y As obj) As obj
   Dim r As New obj
' implemention code for r = x + y
   Return r
End Operator 

ReadOnly Property quote() As String 
   Get 
      Return quoteString
   End Get 
End Property

Public Event Finished()

Delegate Function MathOperator( 
   ByVal x As Double, 
   ByVal y As Double 
) As Double 

Executable Statements

An executable statement performs an action. Statements calling a procedure, branching to another place in the code, looping through several statements, or evaluating an expression are executable statements. An assignment statement is a special case of an executable statement.

Example

The following example demonstrates a decision making statement −

Module decisions
   Sub Main()
      'local variable definition '
      Dim a As Integer = 10

      ' check the boolean condition using if statement '
      If (a < 20) Then
         ' if condition is true then print the following '
         Console.WriteLine("a is less than 20")
      End If
      Console.WriteLine("value of a is : {0}", a)
      Console.ReadLine()
   End Sub
End Module

When the above code is compiled and executed, it produces the following result −

a is less than 20;
value of a is : 10

VB.Net — Directives

The VB.Net compiler directives give instructions to the compiler to preprocess the information before actual compilation starts. All these directives begin with #, and only white-space characters may appear before a directive on a line. These directives are not statements.

VB.Net compiler does not have a separate preprocessor; however, the directives are processed as if there was one. In VB.Net, the compiler directives are used to help in conditional compilation. Unlike C and C++ directives, they are not used to create macros.

Compiler Directives in VB.Net

VB.Net provides the following set of compiler directives −

• The #Const Directive

• The #ExternalSource Directive

• The #If…Then…#Else Directives

• The #Region Directive

The #Const Directive

This directive defines conditional compiler constants. Syntax for this directive is −

#Const constname = expression

Where,

• constname − specifies the name of the constant. Required.

• expression − it is either a literal, or other conditional compiler constant, or a combination including any or all arithmetic or logical operators except Is.

For example,

#Const state = "WEST BENGAL"

Example

The following code demonstrates a hypothetical use of the directive −

Module mydirectives
#Const age = True
Sub Main()
   #If age Then
      Console.WriteLine("You are welcome to the Robotics Club")
   #End If
   Console.ReadKey()
End Sub
End Module

When the above code is compiled and executed, it produces the following result −

You are welcome to the Robotics Club

The #ExternalSource Directive

This directive is used for indicating a mapping between specific lines of source code and text external to the source. It is used only by the compiler and the debugger has no effect on code compilation.

This directive allows including external code from an external code file into a source code file.

Syntax for this directive is −

#ExternalSource( StringLiteral , IntLiteral )
   [ LogicalLine ]
#End ExternalSource

The parameters of #ExternalSource directive are the path of external file, line number of the first line, and the line where the error occurred.

Example

The following code demonstrates a hypothetical use of the directive −

Module mydirectives
   Public Class ExternalSourceTester

      Sub TestExternalSource()

      #ExternalSource("c:vbprogsdirectives.vb", 5)
         Console.WriteLine("This is External Code. ")
      #End ExternalSource

      End Sub
   End Class

   Sub Main()
      Dim t As New ExternalSourceTester()
      t.TestExternalSource()
      Console.WriteLine("In Main.")
      Console.ReadKey()

   End Sub

When the above code is compiled and executed, it produces the following result −

This is External Code.
In Main.

The #If…Then…#Else Directives

This directive conditionally compiles selected blocks of Visual Basic code.

Syntax for this directive is −

#If expression Then
   statements
[ #ElseIf expression Then
   [ statements ]
...
#ElseIf expression Then
   [ statements ] ]
[ #Else
   [ statements ] ]
#End If

For example,

#Const TargetOS = "Linux"
#If TargetOS = "Windows 7" Then
   ' Windows 7 specific code
#ElseIf TargetOS = "WinXP" Then
   ' Windows XP specific code
#Else
   ' Code for other OS
#End if

Example

The following code demonstrates a hypothetical use of the directive −

Module mydirectives
#Const classCode = 8

   Sub Main()
   #If classCode = 7 Then
      Console.WriteLine("Exam Questions for Class VII")
   #ElseIf classCode = 8 Then
      Console.WriteLine("Exam Questions for Class VIII")
   #Else
      Console.WriteLine("Exam Questions for Higher Classes")
   #End If
      Console.ReadKey()

   End Sub
End Module

When the above code is compiled and executed, it produces the following result −

Exam Questions for Class VIII

The #Region Directive

This directive helps in collapsing and hiding sections of code in Visual Basic files.

Syntax for this directive is −

#Region "identifier_string" 
#End Region

For example,

#Region "StatsFunctions" 
   ' Insert code for the Statistical functions here.
#End Region

VB.Net — Operators

An operator is a symbol that tells the compiler to perform specific mathematical or logical manipulations. VB.Net is rich in built-in operators and provides following types of commonly used operators −

• Arithmetic Operators

• Comparison Operators

• Logical/Bitwise Operators

• Bit Shift Operators

• Assignment Operators

• Miscellaneous Operators

This tutorial will explain the most commonly used operators.

Arithmetic Operators

Following table shows all the arithmetic operators supported by VB.Net. Assume variable A holds 2 and variable B holds 7, then −

Show Examples

Comparison Operators

Following table shows all the comparison operators supported by VB.Net. Assume variable A holds 10 and variable B holds 20, then −

Show Examples

Apart from the above, VB.Net provides three more comparison operators, which we will be using in forthcoming chapters; however, we give a brief description here.

• Is Operator − It compares two object reference variables and determines if two object references refer to the same object without performing value comparisons. If object1 and object2 both refer to the exact same object instance, result is True; otherwise, result is False.

• IsNot Operator − It also compares two object reference variables and determines if two object references refer to different objects. If object1 and object2 both refer to the exact same object instance, result is False; otherwise, result is True.

• Like Operator − It compares a string against a pattern.

Logical/Bitwise Operators

Following table shows all the logical operators supported by VB.Net. Assume variable A holds Boolean value True and variable B holds Boolean value False, then −

Show Examples

Bit Shift Operators

We have already discussed the bitwise operators. The bit shift operators perform the shift operations on binary values. Before coming into the bit shift operators, let us understand the bit operations.

Bitwise operators work on bits and perform bit-by-bit operations. The truth tables for &, |, and ^ are as follows −

Assume if A = 60; and B = 13; now in binary format they will be as follows −

A = 0011 1100

B = 0000 1101

——————

A&B = 0000 1100

A|B = 0011 1101

A^B = 0011 0001

~A  = 1100 0011

We have seen that the Bitwise operators supported by VB.Net are And, Or, Xor and Not. The Bit shift operators are >> and << for left shift and right shift, respectively.

Assume that the variable A holds 60 and variable B holds 13, then −

Show Examples

Assignment Operators

There are following assignment operators supported by VB.Net −

Show Examples

Miscellaneous Operators

There are few other important operators supported by VB.Net.

Show Examples

AddHandler Button1.Click,
AddressOf Button1_Click

 
Dim result As res
= Await AsyncMethodThatReturnsResult()
Await AsyncMethod()

MsgBox(GetType(Integer).ToString())

Dim add5 = Function(num As
   Integer) num + 5
'prints 10
Console.WriteLine(add5(5))

Dim num = 5
Console.WriteLine(If(num >= 0,
"Positive", "Negative"))

Operators Precedence in VB.Net

Operator precedence determines the grouping of terms in an expression. This affects how an expression is evaluated. Certain operators have higher precedence than others; for example, the multiplication operator has higher precedence than the addition operator −

For example, x = 7 + 3 * 2; here, x is assigned 13, not 20 because operator * has higher precedence than +, so it first gets multiplied with 3*2 and then adds into 7.

Here, operators with the highest precedence appear at the top of the table, those with the lowest appear at the bottom. Within an expression, higher precedence operators will be evaluated first.

Show Examples

VB.Net — Decision Making

Decision making structures require that the programmer specify one or more conditions to be evaluated or tested by the program, along with a statement or statements to be executed if the condition is determined to be true, and optionally, other statements to be executed if the condition is determined to be false.

Following is the general form of a typical decision making structure found in most of the programming languages −

VB.Net provides the following types of decision making statements. Click the following links to check their details.

VB.Net — Loops

There may be a situation when you need to execute a block of code several number of times. In general, statements are executed sequentially: The first statement in a function is executed first, followed by the second, and so on.

Programming languages provide various control structures that allow for more complicated execution paths.

A loop statement allows us to execute a statement or group of statements multiple times and following is the general form of a loop statement in most of the programming languages −

VB.Net provides following types of loops to handle looping requirements. Click the following links to check their details.

Loop Control Statements

Loop control statements change execution from its normal sequence. When execution leaves a scope, all automatic objects that were created in that scope are destroyed.

VB.Net provides the following control statements. Click the following links to check their details.

VB.Net — Strings

In VB.Net, you can use strings as array of characters, however, more common practice is to use the String keyword to declare a string variable. The string keyword is an alias for the System.String class.

Creating a String Object

You can create string object using one of the following methods −

• By assigning a string literal to a String variable

• By using a String class constructor

• By using the string concatenation operator (+)

• By retrieving a property or calling a method that returns a string

• By calling a formatting method to convert a value or object to its string representation

The following example demonstrates this −

Module strings
   Sub Main()
      Dim fname, lname, fullname, greetings As String
      fname = "Rowan"
      lname = "Atkinson"
      fullname = fname + " " + lname
      Console.WriteLine("Full Name: {0}", fullname)

      'by using string constructor
      Dim letters As Char() = {"H", "e", "l", "l", "o"}
      greetings = New String(letters)
      Console.WriteLine("Greetings: {0}", greetings)

      'methods returning String
      Dim sarray() As String = {"Hello", "From", "Tutorials", "Point"}
      Dim message As String = String.Join(" ", sarray)
      Console.WriteLine("Message: {0}", message)

      'formatting method to convert a value 
      Dim waiting As DateTime = New DateTime(2012, 12, 12, 17, 58, 1)
      Dim chat As String = String.Format("Message sent at {0:t} on {0:D}", waiting)
      Console.WriteLine("Message: {0}", chat)
      Console.ReadLine()
   End Sub
End Module

When the above code is compiled and executed, it produces the following result −

Full Name: Rowan Atkinson
Greetings: Hello
Message: Hello From Tutorials Point
Message: Message sent at 5:58 PM on Wednesday, December 12, 2012

Properties of the String Class

The String class has the following two properties −

Methods of the String Class

The String class has numerous methods that help you in working with the string objects. The following table provides some of the most commonly used methods −

The above list of methods is not exhaustive, please visit MSDN library for the complete list of methods and String class constructors.

Examples

The following example demonstrates some of the methods mentioned above −

Comparing Strings

Module strings
   Sub Main()
      Dim str1, str2 As String
      str1 = "This is test"
      str2 = "This is text"
      
      If (String.Compare(str1, str2) = 0) Then
         Console.WriteLine(str1 + " and " + str2 + " are equal.")
      Else
         Console.WriteLine(str1 + " and " + str2 + " are not equal.")
      End If
      Console.ReadLine()
   End Sub
End Module

When the above code is compiled and executed, it produces the following result −

This is test and This is text are not equal.

String Contains String

Module strings
   Sub Main()
      Dim str1 As String
      str1 = "This is test"
      
      If (str1.Contains("test")) Then
         Console.WriteLine("The sequence 'test' was found.")
      End If
      Console.ReadLine()
   End Sub
End Module

When the above code is compiled and executed, it produces the following result −

The sequence 'test' was found.

Getting a Substring:

Module strings
   Sub Main()
      Dim str As String
      str = "Last night I dreamt of San Pedro"
      Console.WriteLine(str)
      
      Dim substr As String = str.Substring(23)
      Console.WriteLine(substr)
      Console.ReadLine()
   End Sub
End Module

When the above code is compiled and executed, it produces the following result −

Last night I dreamt of San Pedro
San Pedro.

Joining Strings

Module strings
   Sub Main()
      Dim strarray As String() = {
         "Down the way where the nights are gay",
         "And the sun shines daily on the mountain top",
         "I took a trip on a sailing ship",
         "And when I reached Jamaica",
         "I made a stop"
      }
      Dim str As String = String.Join(vbCrLf, strarray)
      Console.WriteLine(str)
      Console.ReadLine()
   End Sub
End Module

When the above code is compiled and executed, it produces the following result −

Down the way where the nights are gay
And the sun shines daily on the mountain top
I took a trip on a sailing ship
And when I reached Jamaica
I made a stop

VB.Net — Date & Time

Most of the softwares you write need implementing some form of date functions returning current date and time. Dates are so much part of everyday life that it becomes easy to work with them without thinking. VB.Net also provides powerful tools for date arithmetic that makes manipulating dates easy.

The Date data type contains date values, time values, or date and time values. The default value of Date is 0:00:00 (midnight) on January 1, 0001. The equivalent .NET data type is System.DateTime.

The DateTime structure represents an instant in time, typically expressed as a date and time of day

'Declaration
<SerializableAttribute> _
Public Structure DateTime _
   Implements IComparable, IFormattable, IConvertible, ISerializable,  
   IComparable(Of DateTime), IEquatable(Of DateTime)

You can also get the current date and time from the DateAndTime class.

The DateAndTime module contains the procedures and properties used in date and time operations.

'Declaration
<StandardModuleAttribute> _
Public NotInheritable Class DateAndTime

Properties and Methods of the DateTime Structure

The following table lists some of the commonly used properties of the DateTime Structure −

The following table lists some of the commonly used methods of the DateTime structure −

The above list of methods is not exhaustive, please visit Microsoft documentation for the complete list of methods and properties of the DateTime structure.

Creating a DateTime Object

You can create a DateTime object in one of the following ways −

• By calling a DateTime constructor from any of the overloaded DateTime constructors.

• By assigning the DateTime object a date and time value returned by a property or method.

• By parsing the string representation of a date and time value.

• By calling the DateTime structure’s implicit default constructor.

The following example demonstrates this −

Module Module1
   Sub Main()
      'DateTime constructor: parameters year, month, day, hour, min, sec
      Dim date1 As New Date(2012, 12, 16, 12, 0, 0)
      'initializes a new DateTime value
      Dim date2 As Date = #12/16/2012 12:00:52 AM#
      'using properties
      Dim date3 As Date = Date.Now
      Dim date4 As Date = Date.UtcNow
      Dim date5 As Date = Date.Today
      
      Console.WriteLine(date1)
      Console.WriteLine(date2)
      Console.WriteLine(date3)
      Console.WriteLine(date4)
      Console.WriteLine(date5)
      Console.ReadKey()
   End Sub
End Module

When the above code was compiled and executed, it produces the following result −

12/16/2012 12:00:00 PM
12/16/2012 12:00:52 PM
12/12/2012 10:22:50 PM
12/12/2012 12:00:00 PM

Getting the Current Date and Time

The following programs demonstrate how to get the current date and time in VB.Net −

Module dateNtime
   Sub Main()
      Console.Write("Current Time: ")
      Console.WriteLine(Now.ToLongTimeString)
      Console.ReadKey()
   End Sub
End Module

When the above code is compiled and executed, it produces the following result −

Current Time: 11 :05 :32 AM

Current Date −

Module dateNtime
   Sub Main()
      Console.WriteLine("Current Date: ")
      Dim dt As Date = Today
      Console.WriteLine("Today is: {0}", dt)
      Console.ReadKey()
   End Sub
End Module

When the above code is compiled and executed, it produces the following result −

Today is: 12/11/2012 12:00:00 AM

Formatting Date

A Date literal should be enclosed within hash signs (# #), and specified in the format M/d/yyyy, for example #12/16/2012#. Otherwise, your code may change depending on the locale in which your application is running.

For example, you specified Date literal of #2/6/2012# for the date February 6, 2012. It is alright for the locale that uses mm/dd/yyyy format. However, in a locale that uses dd/mm/yyyy format, your literal would compile to June 2, 2012. If a locale uses another format say, yyyy/mm/dd, the literal would be invalid and cause a compiler error.

To convert a Date literal to the format of your locale or to a custom format, use the Format function of String class, specifying either a predefined or user-defined date format.

The following example demonstrates this.

Module dateNtime
   Sub Main()
      Console.WriteLine("India Wins Freedom: ")
      Dim independenceDay As New Date(1947, 8, 15, 0, 0, 0)
      ' Use format specifiers to control the date display.
      Console.WriteLine(" Format 'd:' " & independenceDay.ToString("d"))
      Console.WriteLine(" Format 'D:' " & independenceDay.ToString("D"))
      Console.WriteLine(" Format 't:' " & independenceDay.ToString("t"))
      Console.WriteLine(" Format 'T:' " & independenceDay.ToString("T"))
      Console.WriteLine(" Format 'f:' " & independenceDay.ToString("f"))
      Console.WriteLine(" Format 'F:' " & independenceDay.ToString("F"))
      Console.WriteLine(" Format 'g:' " & independenceDay.ToString("g"))
      Console.WriteLine(" Format 'G:' " & independenceDay.ToString("G"))
      Console.WriteLine(" Format 'M:' " & independenceDay.ToString("M"))
      Console.WriteLine(" Format 'R:' " & independenceDay.ToString("R"))
      Console.WriteLine(" Format 'y:' " & independenceDay.ToString("y"))
      Console.ReadKey()
   End Sub
End Module

When the above code is compiled and executed, it produces the following result −

India Wins Freedom:
Format 'd:' 8/15/1947
Format 'D:' Friday, August 15, 1947
Format 't:' 12:00 AM
Format 'T:' 12:00:00 AM
Format 'f:' Friday, August 15, 1947 12:00 AM
Format 'F:' Friday, August 15, 1947 12:00:00 AM
Format 'g:' 8/15/1947 12:00 AM
Format 'G:' 8/15/1947 12:00:00 AM
Format 'M:' 8/15/1947 August 15
Format 'R:' Fri, 15 August 1947 00:00:00 GMT
Format 'y:' August, 1947

Predefined Date/Time Formats

The following table identifies the predefined date and time format names. These may be used by name as the style argument for the Format function −

For other formats like user-defined formats, please consult Microsoft Documentation.

Properties and Methods of the DateAndTime Class

The following table lists some of the commonly used properties of the DateAndTime Class −

The following table lists some of the commonly used methods of the DateAndTime class −

The above list is not exhaustive. For complete list of properties and methods of the DateAndTime class, please consult Microsoft Documentation.

The following program demonstrates some of these and methods −

Module Module1
   Sub Main()
      Dim birthday As Date
      Dim bday As Integer
      Dim month As Integer
      Dim monthname As String
      ' Assign a date using standard short format.
      birthday = #7/27/1998#
      bday = Microsoft.VisualBasic.DateAndTime.Day(birthday)
      month = Microsoft.VisualBasic.DateAndTime.Month(birthday)
      monthname = Microsoft.VisualBasic.DateAndTime.MonthName(month)
      
      Console.WriteLine(birthday)
      Console.WriteLine(bday)
      Console.WriteLine(month)
      Console.WriteLine(monthname)
      Console.ReadKey()
   End Sub
End Module

When the above code is compiled and executed, it produces the following result −

7/27/1998 12:00:00 AM
27
7
July

VB.Net — Arrays

An array stores a fixed-size sequential collection of elements of the same type. An array is used to store a collection of data, but it is often more useful to think of an array as a collection of variables of the same type.

All arrays consist of contiguous memory locations. The lowest address corresponds to the first element and the highest address to the last element.

Creating Arrays in VB.Net

To declare an array in VB.Net, you use the Dim statement. For example,

Dim intData(30)	  ' an array of 31 elements
Dim strData(20) As String	' an array of 21 strings
Dim twoDarray(10, 20) As Integer	'a two dimensional array of integers
Dim ranges(10, 100)	 'a two dimensional array

You can also initialize the array elements while declaring the array. For example,

Dim intData() As Integer = {12, 16, 20, 24, 28, 32}
Dim names() As String = {"Karthik", "Sandhya", _
"Shivangi", "Ashwitha", "Somnath"}
Dim miscData() As Object = {"Hello World", 12d, 16ui, "A"c}

The elements in an array can be stored and accessed by using the index of the array. The following program demonstrates this −

Module arrayApl
   Sub Main()
      Dim n(10) As Integer ' n is an array of 11 integers '
      Dim i, j As Integer
      ' initialize elements of array n '         
      
      For i = 0 To 10
          n(i) = i + 100 ' set element at location i to i + 100 
      Next i
      ' output each array element's value '
      
      For j = 0 To 10
          Console.WriteLine("Element({0}) = {1}", j, n(j))
      Next j
      Console.ReadKey()
   End Sub
End Module

When the above code is compiled and executed, it produces the following result −

Element(0) = 100
Element(1) = 101
Element(2) = 102
Element(3) = 103
Element(4) = 104
Element(5) = 105
Element(6) = 106
Element(7) = 107
Element(8) = 108
Element(9) = 109
Element(10) = 110

Dynamic Arrays

Dynamic arrays are arrays that can be dimensioned and re-dimensioned as par the need of the program. You can declare a dynamic array using the ReDim statement.

Syntax for ReDim statement −

ReDim [Preserve] arrayname(subscripts)

Where,

• The Preserve keyword helps to preserve the data in an existing array, when you resize it.

• arrayname is the name of the array to re-dimension.

• subscripts specifies the new dimension.

Module arrayApl
   Sub Main()
      Dim marks() As Integer
      ReDim marks(2)
      marks(0) = 85
      marks(1) = 75
      marks(2) = 90
     
      ReDim Preserve marks(10)
      marks(3) = 80
      marks(4) = 76
      marks(5) = 92
      marks(6) = 99
      marks(7) = 79
      marks(8) = 75
      
      For i = 0 To 10
         Console.WriteLine(i & vbTab & marks(i))
      Next i
      Console.ReadKey()
   End Sub
End Module

When the above code is compiled and executed, it produces the following result −

0	85
1	75
2	90
3	80
4	76
5	92
6	99
7	79
8	75
9	0
10	0

Multi-Dimensional Arrays

VB.Net allows multidimensional arrays. Multidimensional arrays are also called rectangular arrays.

You can declare a 2-dimensional array of strings as −

Dim twoDStringArray(10, 20) As String

or, a 3-dimensional array of Integer variables −

Dim threeDIntArray(10, 10, 10) As Integer

The following program demonstrates creating and using a 2-dimensional array −

Module arrayApl
   Sub Main()
      ' an array with 5 rows and 2 columns
      Dim a(,) As Integer = {{0, 0}, {1, 2}, {2, 4}, {3, 6}, {4, 8}}
      Dim i, j As Integer
      ' output each array element's value '
      
      For i = 0 To 4
          For j = 0 To 1
              Console.WriteLine("a[{0},{1}] = {2}", i, j, a(i, j))
          Next j
      Next i
      Console.ReadKey()
   End Sub
End Module

When the above code is compiled and executed, it produces the following result −

a[0,0]: 0
a[0,1]: 0
a[1,0]: 1
a[1,1]: 2
a[2,0]: 2
a[2,1]: 4
a[3,0]: 3
a[3,1]: 6
a[4,0]: 4
a[4,1]: 8

Jagged Array

A Jagged array is an array of arrays. The following code shows declaring a jagged array named scores of Integers −

Dim scores As Integer()() = New Integer(5)(){}

The following example illustrates using a jagged array −

Module arrayApl
   Sub Main()
      'a jagged array of 5 array of integers
      Dim a As Integer()() = New Integer(4)() {}
      a(0) = New Integer() {0, 0}
      a(1) = New Integer() {1, 2}
      a(2) = New Integer() {2, 4}
      a(3) = New Integer() {3, 6}
      a(4) = New Integer() {4, 8}
      Dim i, j As Integer
      ' output each array element's value 
      
      For i = 0 To 4
         For j = 0 To 1
            Console.WriteLine("a[{0},{1}] = {2}", i, j, a(i)(j))
         Next j
      Next i
      Console.ReadKey()
   End Sub
End Module

When the above code is compiled and executed, it produces the following result −

a[0][0]: 0
a[0][1]: 0
a[1][0]: 1
a[1][1]: 2
a[2][0]: 2
a[2][1]: 4
a[3][0]: 3
a[3][1]: 6
a[4][0]: 4
a[4][1]: 8

The Array Class

The Array class is the base class for all the arrays in VB.Net. It is defined in the System namespace. The Array class provides various properties and methods to work with arrays.

Properties of the Array Class

The following table provides some of the most commonly used properties of the Array class −

Methods of the Array Class

The following table provides some of the most commonly used methods of the Array class −

For complete list of Array class properties and methods, please consult Microsoft documentation.

Example

The following program demonstrates use of some of the methods of the Array class:

Module arrayApl
   Sub Main()
      Dim list As Integer() = {34, 72, 13, 44, 25, 30, 10}
      Dim temp As Integer() = list
      Dim i As Integer
      Console.Write("Original Array: ")
      
      For Each i In list
         Console.Write("{0} ", i)
      Next i
      Console.WriteLine()
      ' reverse the array
      Array.Reverse(temp)
      Console.Write("Reversed Array: ")
      
      For Each i In temp
         Console.Write("{0} ", i)
      Next i
      Console.WriteLine()
      'sort the array
      Array.Sort(list)
      Console.Write("Sorted Array: ")
      
      For Each i In list
         Console.Write("{0} ", i)
      Next i
      Console.WriteLine()
      Console.ReadKey()
   End Sub
End Module

When the above code is compiled and executed, it produces the following result −

Original Array: 34 72 13 44 25 30 10
Reversed Array: 10 30 25 44 13 72 34
Sorted Array: 10 13 25 30 34 44 72

VB.Net — Collections

Collection classes are specialized classes for data storage and retrieval. These classes provide support for stacks, queues, lists, and hash tables. Most collection classes implement the same interfaces.

Collection classes serve various purposes, such as allocating memory dynamically to elements and accessing a list of items on the basis of an index, etc. These classes create collections of objects of the Object class, which is the base class for all data types in VB.Net.

Various Collection Classes and Their Usage

The following are the various commonly used classes of the System.Collection namespace. Click the following links to check their details.

VB.Net — Functions

A procedure is a group of statements that together perform a task when called. After the procedure is executed, the control returns to the statement calling the procedure. VB.Net has two types of procedures −

• Functions

• Sub procedures or Subs

Functions return a value, whereas Subs do not return a value.

Defining a Function

The Function statement is used to declare the name, parameter and the body of a function. The syntax for the Function statement is −

[Modifiers] Function FunctionName [(ParameterList)] As ReturnType
   [Statements]
End Function

Where,

• Modifiers − specify the access level of the function; possible values are: Public, Private, Protected, Friend, Protected Friend and information regarding overloading, overriding, sharing, and shadowing.

• FunctionName − indicates the name of the function

• ParameterList − specifies the list of the parameters

• ReturnType − specifies the data type of the variable the function returns

Example

Following code snippet shows a function FindMax that takes two integer values and returns the larger of the two.

Function FindMax(ByVal num1 As Integer, ByVal num2 As Integer) As Integer
   ' local variable declaration */
   Dim result As Integer
   
   If (num1 > num2) Then
      result = num1
   Else
      result = num2
   End If
   FindMax = result
End Function

Function Returning a Value

In VB.Net, a function can return a value to the calling code in two ways −

• By using the return statement

• By assigning the value to the function name

The following example demonstrates using the FindMax function −

Module myfunctions
   Function FindMax(ByVal num1 As Integer, ByVal num2 As Integer) As Integer
      ' local variable declaration */
      Dim result As Integer
      
      If (num1 > num2) Then
         result = num1
      Else
         result = num2
      End If
      FindMax = result
   End Function
   Sub Main()
      Dim a As Integer = 100
      Dim b As Integer = 200
      Dim res As Integer
      
      res = FindMax(a, b)
      Console.WriteLine("Max value is : {0}", res)
      Console.ReadLine()
   End Sub
End Module

When the above code is compiled and executed, it produces the following result −

Max value is : 200

Recursive Function

A function can call itself. This is known as recursion. Following is an example that calculates factorial for a given number using a recursive function −

Module myfunctions
   Function factorial(ByVal num As Integer) As Integer
      ' local variable declaration */
      Dim result As Integer
      
      If (num = 1) Then
         Return 1
      Else
         result = factorial(num - 1) * num
         Return result
      End If
   End Function
   Sub Main()
      'calling the factorial method
      Console.WriteLine("Factorial of 6 is : {0}", factorial(6))
      Console.WriteLine("Factorial of 7 is : {0}", factorial(7))
      Console.WriteLine("Factorial of 8 is : {0}", factorial(8))
      Console.ReadLine()
   End Sub
End Module

When the above code is compiled and executed, it produces the following result −

Factorial of 6 is: 720
Factorial of 7 is: 5040
Factorial of 8 is: 40320

Param Arrays

At times, while declaring a function or sub procedure, you are not sure of the number of arguments passed as a parameter.
VB.Net param arrays (or parameter arrays) come into help at these times.

The following example demonstrates this −

Module myparamfunc
   Function AddElements(ParamArray arr As Integer()) As Integer
      Dim sum As Integer = 0
      Dim i As Integer = 0
      
      For Each i In arr
         sum += i
      Next i
      Return sum
   End Function
   Sub Main()
      Dim sum As Integer
      sum = AddElements(512, 720, 250, 567, 889)
      Console.WriteLine("The sum is: {0}", sum)
      Console.ReadLine()
   End Sub
End Module

When the above code is compiled and executed, it produces the following result −

The sum is: 2938

Passing Arrays as Function Arguments

You can pass an array as a function argument in VB.Net. The following example demonstrates this −

Module arrayParameter
   Function getAverage(ByVal arr As Integer(), ByVal size As Integer) As Double
      'local variables
      Dim i As Integer
      Dim avg As Double
      Dim sum As Integer = 0
      
      For i = 0 To size - 1
         sum += arr(i)
      Next i
      avg = sum / size
      Return avg
   End Function
   Sub Main()
      ' an int array with 5 elements '
      Dim balance As Integer() = {1000, 2, 3, 17, 50}
      Dim avg As Double
      'pass pointer to the array as an argument 
      avg = getAverage(balance, 5)
      ' output the returned value '
      Console.WriteLine("Average value is: {0} ", avg)
      Console.ReadLine()
   End Sub
End Module

When the above code is compiled and executed, it produces the following result −

Average value is: 214.4

VB.Net — Sub Procedures

As we mentioned in the previous chapter, Sub procedures are procedures that do not return any value. We have been using the Sub procedure Main in all our examples. We have been writing console applications so far in these tutorials. When these applications start, the control goes to the Main Sub procedure, and it in turn, runs any other statements constituting the body of the program.

Defining Sub Procedures

The Sub statement is used to declare the name, parameter and the body of a sub procedure. The syntax for the Sub statement is −

[Modifiers] Sub SubName [(ParameterList)] 
   [Statements]
End Sub

Where,

• Modifiers − specify the access level of the procedure; possible values are — Public, Private, Protected, Friend, Protected Friend and information regarding overloading, overriding, sharing, and shadowing.

• SubName − indicates the name of the Sub

• ParameterList − specifies the list of the parameters

Example

The following example demonstrates a Sub procedure CalculatePay that takes two parameters hours and wages and displays the total pay of an employee −

Module mysub
   Sub CalculatePay(ByRef hours As Double, ByRef wage As Decimal)
      'local variable declaration
      Dim pay As Double
      pay = hours * wage
      Console.WriteLine("Total Pay: {0:C}", pay)
   End Sub
   Sub Main()
      'calling the CalculatePay Sub Procedure
      CalculatePay(25, 10)
      CalculatePay(40, 20)
      CalculatePay(30, 27.5)
      Console.ReadLine()
   End Sub
End Module

When the above code is compiled and executed, it produces the following result −

Total Pay: $250.00
Total Pay: $800.00
Total Pay: $825.00

Passing Parameters by Value

This is the default mechanism for passing parameters to a method. In this mechanism, when a method is called, a new storage location is created for each value parameter. The values of the actual parameters are copied into them. So, the changes made to the parameter inside the method have no effect on the argument.

In VB.Net, you declare the reference parameters using the ByVal keyword. The following example demonstrates the concept −

Module paramByval
   Sub swap(ByVal x As Integer, ByVal y As Integer)
      Dim temp As Integer
      temp = x ' save the value of x 
      x = y    ' put y into x 
      y = temp 'put temp into y 
   End Sub
   Sub Main()
      ' local variable definition 
      Dim a As Integer = 100
      Dim b As Integer = 200
      Console.WriteLine("Before swap, value of a : {0}", a)
      Console.WriteLine("Before swap, value of b : {0}", b)
      ' calling a function to swap the values '
      swap(a, b)
      Console.WriteLine("After swap, value of a : {0}", a)
      Console.WriteLine("After swap, value of b : {0}", b)
      Console.ReadLine()
   End Sub
End Module

When the above code is compiled and executed, it produces the following result −

Before swap, value of a :100
Before swap, value of b :200
After swap, value of a :100
After swap, value of b :200

It shows that there is no change in the values though they had been changed inside the function.

Passing Parameters by Reference

A reference parameter is a reference to a memory location of a variable. When you pass parameters by reference, unlike value parameters, a new storage location is not created for these parameters. The reference parameters represent the same memory location as the actual parameters that are supplied to the method.

In VB.Net, you declare the reference parameters using the ByRef keyword. The following example demonstrates this −

Module paramByref
   Sub swap(ByRef x As Integer, ByRef y As Integer)
      Dim temp As Integer
      temp = x ' save the value of x 
      x = y    ' put y into x 
      y = temp 'put temp into y 
   End Sub
   Sub Main()
      ' local variable definition 
      Dim a As Integer = 100
      Dim b As Integer = 200
      Console.WriteLine("Before swap, value of a : {0}", a)
      Console.WriteLine("Before swap, value of b : {0}", b)
      ' calling a function to swap the values '
      swap(a, b)
      Console.WriteLine("After swap, value of a : {0}", a)
      Console.WriteLine("After swap, value of b : {0}", b)
      Console.ReadLine()
   End Sub
End Module

When the above code is compiled and executed, it produces the following result −

Before swap, value of a : 100
Before swap, value of b : 200
After swap, value of a : 200
After swap, value of b : 100

VB.Net — Classes & Objects

When you define a class, you define a blueprint for a data type. This doesn’t actually define any data, but it does define what the class name means, that is, what an object of the class will consist of and what operations can be performed on such an object.

Objects are instances of a class. The methods and variables that constitute a class are called members of the class.

Class Definition

A class definition starts with the keyword Class followed by the class name; and the class body, ended by the End Class statement. Following is the general form of a class definition −

[ <attributelist> ] [ accessmodifier ] [ Shadows ] [ MustInherit | NotInheritable ] [ Partial ] _
Class name [ ( Of typelist ) ]
   [ Inherits classname ]
   [ Implements interfacenames ]
   [ statements ]
End Class

Where,

• attributelist is a list of attributes that apply to the class. Optional.

• accessmodifier defines the access levels of the class, it has values as — Public, Protected, Friend, Protected Friend and Private. Optional.

• Shadows indicate that the variable re-declares and hides an identically named element, or set of overloaded elements, in a base class. Optional.

• MustInherit specifies that the class can be used only as a base class and that you cannot create an object directly from it, i.e., an abstract class. Optional.

• NotInheritable specifies that the class cannot be used as a base class.

• Partial indicates a partial definition of the class.

• Inherits specifies the base class it is inheriting from.

• Implements specifies the interfaces the class is inheriting from.

The following example demonstrates a Box class, with three data members, length, breadth and height −

Module mybox
   Class Box
      Public length As Double   ' Length of a box
      Public breadth As Double  ' Breadth of a box
      Public height As Double   ' Height of a box
   End Class
   Sub Main()
      Dim Box1 As Box = New Box()        ' Declare Box1 of type Box
      Dim Box2 As Box = New Box()        ' Declare Box2 of type Box
      Dim volume As Double = 0.0         ' Store the volume of a box here
      
      ' box 1 specification
      Box1.height = 5.0
      Box1.length = 6.0
      Box1.breadth = 7.0
      
      ' box 2 specification
      Box2.height = 10.0
      Box2.length = 12.0	
      Box2.breadth = 13.0
      
      'volume of box 1
      volume = Box1.height * Box1.length * Box1.breadth
      Console.WriteLine("Volume of Box1 : {0}", volume)
      
      'volume of box 2
      volume = Box2.height * Box2.length * Box2.breadth
      Console.WriteLine("Volume of Box2 : {0}", volume)
      Console.ReadKey()
   End Sub
End Module

When the above code is compiled and executed, it produces the following result −

Volume of Box1 : 210
Volume of Box2 : 1560

Member Functions and Encapsulation

A member function of a class is a function that has its definition or its prototype within the class definition like any other variable. It operates on any object of the class of which it is a member and has access to all the members of a class for that object.

Member variables are attributes of an object (from design perspective) and they are kept private to implement encapsulation. These variables can only be accessed using the public member functions.

Let us put above concepts to set and get the value of different class members in a class −

Module mybox
   Class Box
      Public length As Double    ' Length of a box
      Public breadth As Double   ' Breadth of a box
      Public height As Double    ' Height of a box
      Public Sub setLength(ByVal len As Double)
         length = len
      End Sub
      
      Public Sub setBreadth(ByVal bre As Double)
         breadth = bre
      End Sub
      
      Public Sub setHeight(ByVal hei As Double)
         height = hei
      End Sub
      
      Public Function getVolume() As Double
         Return length * breadth * height
      End Function
   End Class
   Sub Main()
      Dim Box1 As Box = New Box()        ' Declare Box1 of type Box
      Dim Box2 As Box = New Box()        ' Declare Box2 of type Box
      Dim volume As Double = 0.0         ' Store the volume of a box here

      ' box 1 specification
      Box1.setLength(6.0)
      Box1.setBreadth(7.0)
      Box1.setHeight(5.0)
      
      'box 2 specification
      Box2.setLength(12.0)
      Box2.setBreadth(13.0)
      Box2.setHeight(10.0)
      
      ' volume of box 1
      volume = Box1.getVolume()
      Console.WriteLine("Volume of Box1 : {0}", volume)

      'volume of box 2
      volume = Box2.getVolume()
      Console.WriteLine("Volume of Box2 : {0}", volume)
      Console.ReadKey()
   End Sub
End Module

When the above code is compiled and executed, it produces the following result −

Volume of Box1 : 210
Volume of Box2 : 1560

Constructors and Destructors

A class constructor is a special member Sub of a class that is executed whenever we create new objects of that class. A constructor has the name New and it does not have any return type.

Following program explains the concept of constructor −

Class Line
   Private length As Double    ' Length of a line
   Public Sub New()   'constructor
      Console.WriteLine("Object is being created")
   End Sub
   
   Public Sub setLength(ByVal len As Double)
      length = len
   End Sub
     
   Public Function getLength() As Double
      Return length
   End Function
   Shared Sub Main()
      Dim line As Line = New Line()
      'set line length
      line.setLength(6.0)
      Console.WriteLine("Length of line : {0}", line.getLength())
      Console.ReadKey()
   End Sub
End Class

When the above code is compiled and executed, it produces the following result −

Object is being created
Length of line : 6

A default constructor does not have any parameter, but if you need, a constructor can have parameters. Such constructors are called parameterized constructors. This technique helps you to assign initial value to an object at the time of its creation as shown in the following example −

Class Line
   Private length As Double    ' Length of a line
   Public Sub New(ByVal len As Double)   'parameterised constructor
      Console.WriteLine("Object is being created, length = {0}", len)
      length = len
   End Sub
   Public Sub setLength(ByVal len As Double)
      length = len
   End Sub
       
   Public Function getLength() As Double
      Return length
   End Function
   Shared Sub Main()
      Dim line As Line = New Line(10.0)
      Console.WriteLine("Length of line set by constructor : {0}", line.getLength())
      'set line length
      line.setLength(6.0)
      Console.WriteLine("Length of line set by setLength : {0}", line.getLength())
      Console.ReadKey()
   End Sub
End Class

When the above code is compiled and executed, it produces the following result −

Object is being created, length = 10
Length of line set by constructor : 10
Length of line set by setLength : 6

A destructor is a special member Sub of a class that is executed whenever an object of its class goes out of scope.

A destructor has the name Finalize and it can neither return a value nor can it take any parameters. Destructor can be very useful for releasing resources before coming out of the program like closing files, releasing memories, etc.

Destructors cannot be inherited or overloaded.

Following example explains the concept of destructor −

Class Line
   Private length As Double    ' Length of a line
   Public Sub New()   'parameterised constructor
      Console.WriteLine("Object is being created")
   End Sub
   
   Protected Overrides Sub Finalize()  ' destructor
      Console.WriteLine("Object is being deleted")
   End Sub
   
   Public Sub setLength(ByVal len As Double)
      length = len
   End Sub
   
   Public Function getLength() As Double
      Return length
   End Function
   
   Shared Sub Main()
      Dim line As Line = New Line()
      'set line length
      line.setLength(6.0)
      Console.WriteLine("Length of line : {0}", line.getLength())
      Console.ReadKey()
   End Sub
End Class

When the above code is compiled and executed, it produces the following result −

Object is being created
Length of line : 6
Object is being deleted

Shared Members of a VB.Net Class

We can define class members as static using the Shared keyword. When we declare a member of a class as Shared, it means no matter how many objects of the class are created, there is only one copy of the member.

The keyword Shared implies that only one instance of the member exists for a class. Shared variables are used for defining constants because their values can be retrieved by invoking the class without creating an instance of it.

Shared variables can be initialized outside the member function or class definition. You can also initialize Shared variables inside the class definition.

You can also declare a member function as Shared. Such functions can access only Shared variables. The Shared functions exist even before the object is created.

The following example demonstrates the use of shared members −

Class StaticVar
   Public Shared num As Integer
   Public Sub count()
      num = num + 1
   End Sub
   Public Shared Function getNum() As Integer
      Return num
   End Function
   Shared Sub Main()
      Dim s As StaticVar = New StaticVar()
      s.count()
      s.count()
      s.count()
      Console.WriteLine("Value of variable num: {0}", StaticVar.getNum())
      Console.ReadKey()
   End Sub
End Class

When the above code is compiled and executed, it produces the following result −

Value of variable num: 3

Inheritance

One of the most important concepts in object-oriented programming is that of inheritance. Inheritance allows us to define a class in terms of another class which makes it easier to create and maintain an application. This also provides an opportunity to reuse the code functionality and fast implementation time.

When creating a class, instead of writing completely new data members and member functions, the programmer can designate that the new class should inherit the members of an existing class. This existing class is called the base class, and the new class is referred to as the derived class.

Base & Derived Classes

A class can be derived from more than one class or interface, which means that it can inherit data and functions from multiple base classes or interfaces.

The syntax used in VB.Net for creating derived classes is as follows −

<access-specifier> Class <base_class>
...
End Class
Class <derived_class>: Inherits <base_class>
...
End Class

Consider a base class Shape and its derived class Rectangle −

' Base class
Class Shape
   Protected width As Integer
   Protected height As Integer
   Public Sub setWidth(ByVal w As Integer)
      width = w
   End Sub
   Public Sub setHeight(ByVal h As Integer)
      height = h
   End Sub
End Class
' Derived class
Class Rectangle : Inherits Shape
   Public Function getArea() As Integer
      Return (width * height)
   End Function
End Class
Class RectangleTester
   Shared Sub Main()
      Dim rect As Rectangle = New Rectangle()
      rect.setWidth(5)
      rect.setHeight(7)
      ' Print the area of the object.
      Console.WriteLine("Total area: {0}", rect.getArea())
      Console.ReadKey()
   End Sub	
End Class

When the above code is compiled and executed, it produces the following result −

Total area: 35

Base Class Initialization

The derived class inherits the base class member variables and member methods. Therefore, the super class object should be created before the subclass is created. The super class or the base class is implicitly known as MyBase in VB.Net

The following program demonstrates this −

' Base class
Class Rectangle
   Protected width As Double
   Protected length As Double
   Public Sub New(ByVal l As Double, ByVal w As Double)
      length = l
      width = w
   End Sub
   Public Function GetArea() As Double
      Return (width * length)
   End Function
   Public Overridable Sub Display()
      Console.WriteLine("Length: {0}", length)
      Console.WriteLine("Width: {0}", width)
      Console.WriteLine("Area: {0}", GetArea())
   End Sub
   'end class Rectangle  
End Class

'Derived class
Class Tabletop : Inherits Rectangle
   Private cost As Double
   Public Sub New(ByVal l As Double, ByVal w As Double)
      MyBase.New(l, w)
   End Sub
   Public Function GetCost() As Double
      Dim cost As Double
      cost = GetArea() * 70
      Return cost
   End Function
   Public Overrides Sub Display()
      MyBase.Display()
      Console.WriteLine("Cost: {0}", GetCost())
   End Sub
    'end class Tabletop
End Class
Class RectangleTester
   Shared Sub Main()
      Dim t As Tabletop = New Tabletop(4.5, 7.5)
      t.Display()
      Console.ReadKey()
   End Sub
End Class

When the above code is compiled and executed, it produces the following result −

Length: 4.5
Width: 7.5
Area: 33.75
Cost: 2362.5

VB.Net supports multiple inheritance.

VB.Net — Exception Handling

An exception is a problem that arises during the execution of a program. An exception is a response to an exceptional circumstance that arises while a program is running, such as an attempt to divide by zero.

Exceptions provide a way to transfer control from one part of a program to another. VB.Net exception handling is built upon four keywords — Try, Catch, Finally and Throw.

• Try − A Try block identifies a block of code for which particular exceptions will be activated. It’s followed by one or more Catch blocks.

• Catch − A program catches an exception with an exception handler at the place in a program where you want to handle the problem. The Catch keyword indicates the catching of an exception.

• Finally − The Finally block is used to execute a given set of statements, whether an exception is thrown or not thrown. For example, if you open a file, it must be closed whether an exception is raised or not.

• Throw − A program throws an exception when a problem shows up. This is done using a Throw keyword.

Syntax

Assuming a block will raise an exception, a method catches an exception using a combination of the Try and Catch keywords. A Try/Catch block is placed around the code that might generate an exception. Code within a Try/Catch block is referred to as protected code, and the syntax for using Try/Catch looks like the following −

Try
   [ tryStatements ]
   [ Exit Try ]
[ Catch [ exception [ As type ] ] [ When expression ]
   [ catchStatements ]
   [ Exit Try ] ]
[ Catch ... ]
[ Finally
   [ finallyStatements ] ]
End Try

You can list down multiple catch statements to catch different type of exceptions in case your try block raises more than one exception in different situations.

Exception Classes in .Net Framework

In the .Net Framework, exceptions are represented by classes. The exception classes in .Net Framework are mainly directly or indirectly derived from the System.Exception class. Some of the exception classes derived from the System.Exception class are the System.ApplicationException and System.SystemException classes.

The System.ApplicationException class supports exceptions generated by application programs. So the exceptions defined by the programmers should derive from this class.

The System.SystemException class is the base class for all predefined system exception.

The following table provides some of the predefined exception classes derived from the Sytem.SystemException class −

Handling Exceptions

VB.Net provides a structured solution to the exception handling problems in the form of try and catch blocks. Using these blocks the core program statements are separated from the error-handling statements.

These error handling blocks are implemented using the Try, Catch and Finally keywords. Following is an example of throwing an exception when dividing by zero condition occurs −

Module exceptionProg
   Sub division(ByVal num1 As Integer, ByVal num2 As Integer)
      Dim result As Integer
      Try
         result = num1  num2
      Catch e As DivideByZeroException
         Console.WriteLine("Exception caught: {0}", e)
      Finally
         Console.WriteLine("Result: {0}", result)
      End Try
   End Sub
   Sub Main()
      division(25, 0)
      Console.ReadKey()
  End Sub
End Module

When the above code is compiled and executed, it produces the following result −

Exception caught: System.DivideByZeroException: Attempted to divide by zero. 
at ...
Result: 0

Creating User-Defined Exceptions

You can also define your own exception. User-defined exception classes are derived from the ApplicationException class. The following example demonstrates this −

Module exceptionProg
   Public Class TempIsZeroException : Inherits ApplicationException
      Public Sub New(ByVal message As String)
         MyBase.New(message)
      End Sub
   End Class
   Public Class Temperature
      Dim temperature As Integer = 0
      Sub showTemp()
         If (temperature = 0) Then
            Throw (New TempIsZeroException("Zero Temperature found"))
         Else
            Console.WriteLine("Temperature: {0}", temperature)
         End If
      End Sub
   End Class
   Sub Main()
      Dim temp As Temperature = New Temperature()
      Try
         temp.showTemp()
      Catch e As TempIsZeroException
         Console.WriteLine("TempIsZeroException: {0}", e.Message)
      End Try
      Console.ReadKey()
   End Sub
End Module

When the above code is compiled and executed, it produces the following result −

TempIsZeroException: Zero Temperature found

Throwing Objects

You can throw an object if it is either directly or indirectly derived from the System.Exception class.

You can use a throw statement in the catch block to throw the present object as −

Throw [ expression ]

The following program demonstrates this −

Module exceptionProg
   Sub Main()
      Try
         Throw New ApplicationException("A custom exception _ is being thrown here...")
      Catch e As Exception
         Console.WriteLine(e.Message)
      Finally
         Console.WriteLine("Now inside the Finally Block")
      End Try
      Console.ReadKey()
   End Sub
End Module

When the above code is compiled and executed, it produces the following result −

A custom exception is being thrown here...
Now inside the Finally Block

VB.Net — File Handling

A file is a collection of data stored in a disk with a specific name and a directory path. When a file is opened for reading or writing, it becomes a stream.

The stream is basically the sequence of bytes passing through the communication path. There are two main streams: the input stream and the output stream. The input stream is used for reading data from file (read operation) and the output stream is used for writing into the file (write operation).

VB.Net I/O Classes

The System.IO namespace has various classes that are used for performing various operations with files, like creating and deleting files, reading from or writing to a file, closing a file, etc.

The following table shows some commonly used non-abstract classes in the System.IO namespace −

The FileStream Class

The FileStream class in the System.IO namespace helps in reading from, writing to and closing files. This class derives from the abstract class Stream.

You need to create a FileStream object to create a new file or open an existing file. The syntax for creating a FileStream object is as follows −

Dim <object_name> As FileStream = New FileStream(<file_name>, <FileMode Enumerator>, <FileAccess Enumerator>, <FileShare Enumerator>)

For example, for creating a FileStream object F for reading a file named sample.txt −

Dim f1 As FileStream = New FileStream("sample.txt", FileMode.OpenOrCreate, FileAccess.ReadWrite)

Example

The following program demonstrates use of the FileStream class −

Imports System.IO
Module fileProg
   Sub Main()
      Dim f1 As FileStream = New FileStream("sample.txt", _ FileMode.OpenOrCreate, FileAccess.ReadWrite)
      Dim i As Integer
      
      For i = 0 To 20
         f1.WriteByte(CByte(i))
      Next i
      f1.Position = 0
      
      For i = 0 To 20
         Console.Write("{0} ", f1.ReadByte())
      Next i
      f1.Close()
      Console.ReadKey()
   End Sub
End Module

When the above code is compiled and executed, it produces the following result −

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 -1

Advanced File Operations in VB.Net

The preceding example provides simple file operations in VB.Net. However, to utilize the immense powers of System.IO classes, you need to know the commonly used properties and methods of these classes.

We will discuss these classes and the operations they perform in the following sections. Please click the links provided to get to the individual sections −

VB.Net — Basic Controls

An object is a type of user interface element you create on a Visual Basic form by using a toolbox control. In fact, in Visual Basic, the form itself is an object. Every Visual Basic control consists of three important elements −

• Properties which describe the object,

• Methods cause an object to do something and

• Events are what happens when an object does something.

Control Properties

All the Visual Basic Objects can be moved, resized or customized by setting their properties. A property is a value or characteristic held by a Visual Basic object, such as Caption or Fore Color.

Properties can be set at design time by using the Properties window or at run time by using statements in the program code.

Object. Property = Value

Where

• Object is the name of the object you’re customizing.

• Property is the characteristic you want to change.

• Value is the new property setting.

For example,

Form1.Caption = "Hello"

You can set any of the form properties using Properties Window. Most of the properties can be set or read during application execution. You can refer to Microsoft documentation for a complete list of properties associated with different controls and restrictions applied to them.

Control Methods

A method is a procedure created as a member of a class and they cause an object to do something. Methods are used to access or manipulate the characteristics of an object or a variable. There are mainly two categories of methods you will use in your classes −

• If you are using a control such as one of those provided by the Toolbox, you can call any of its public methods. The requirements of such a method depend on the class being used.

• If none of the existing methods can perform your desired task, you can add a method to a class.

For example, the MessageBox control has a method named Show, which is called in the code snippet below −

Public Class Form1
   Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) 
   Handles Button1.Click
      MessageBox.Show("Hello, World")
   End Sub
End Class

Control Events

An event is a signal that informs an application that something important has occurred. For example, when a user clicks a control on a form, the form can raise a Click event and call a procedure that handles the event. There are various types of events associated with a Form like click, double click, close, load, resize, etc.

Following is the default structure of a form Load event handler subroutine. You can see this code by double clicking the code which will give you a complete list of the all events associated with Form control −

Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
   'event handler code goes here
End Sub

Here, Handles MyBase.Load indicates that Form1_Load() subroutine handles Load event. Similar way, you can check stub code for click, double click. If you want to initialize some variables like properties, etc., then you will keep such code inside Form1_Load() subroutine. Here, important point to note is the name of the event handler, which is by default Form1_Load, but you can change this name based on your naming convention you use in your application programming.

Basic Controls

VB.Net provides a huge variety of controls that help you to create rich user interface. Functionalities of all these controls are defined in the respective control classes. The control classes are defined in the System.Windows.Forms namespace.

The following table lists some of the commonly used controls −

VB.Net — Dialog Boxes

There are many built-in dialog boxes to be used in Windows forms for various tasks like opening and saving files, printing a page, providing choices for colors, fonts, page setup, etc., to the user of an application. These built-in dialog boxes reduce the developer’s time and workload.

All of these dialog box control classes inherit from the CommonDialog class and override the RunDialog() function of the base class to create the specific dialog box.

The RunDialog() function is automatically invoked when a user of a dialog box calls its ShowDialog() function.

The ShowDialog method is used to display all the dialog box controls at run-time. It returns a value of the type of DialogResult enumeration. The values of DialogResult enumeration are −

• Abort − returns DialogResult.Abort value, when user clicks an Abort button.

• Cancel − returns DialogResult.Cancel, when user clicks a Cancel button.

• Ignore − returns DialogResult.Ignore, when user clicks an Ignore button.

• No − returns DialogResult.No, when user clicks a No button.

• None − returns nothing and the dialog box continues running.

• OK − returns DialogResult.OK, when user clicks an OK button

• Retry − returns DialogResult.Retry , when user clicks an Retry button

• Yes − returns DialogResult.Yes, when user clicks an Yes button

The following diagram shows the common dialog class inheritance −

All these above-mentioned classes have corresponding controls that could be added from the Toolbox during design time. You can include relevant functionality of these classes to your application, either by instantiating the class programmatically or by using relevant controls.

When you double click any of the dialog controls in the toolbox or drag the control onto the form, it appears in the Component tray at the bottom of the Windows Forms Designer, they do not directly show up on the form.

The following table lists the commonly used dialog box controls. Click the following links to check their detail −

VB.Net — Advanced Form

In this chapter, let us study the following concepts −

• Adding menus and sub menus in an application

• Adding the cut, copy and paste functionalities in a form

• Anchoring and docking controls in a form

• Modal forms

Adding Menus and Sub Menus in an Application

Traditionally, the Menu, MainMenu, ContextMenu, and MenuItem classes were used for adding menus, sub-menus and context menus in a Windows application.

Now, the MenuStrip, the ToolStripMenuItem, ToolStripDropDown and ToolStripDropDownMenu controls replace and add functionality to the Menu-related controls of previous versions. However, the old control classes are retained for both backward compatibility and future use.

Let us create a typical windows main menu bar and sub menus using the old version controls first since these controls are still much used in old applications.

Following is an example, which shows how we create a menu bar with menu items: File, Edit, View and Project. The File menu has the sub menus New, Open and Save.

Let’s double click on the Form and put the following code in the opened window.

Public Class Form1
   Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
      'defining the main menu bar
      Dim mnuBar As New MainMenu()
      'defining the menu items for the main menu bar
      Dim myMenuItemFile As New MenuItem("&File")
      Dim myMenuItemEdit As New MenuItem("&Edit")
      Dim myMenuItemView As New MenuItem("&View")
      Dim myMenuItemProject As New MenuItem("&Project")

      'adding the menu items to the main menu bar
      mnuBar.MenuItems.Add(myMenuItemFile)
      mnuBar.MenuItems.Add(myMenuItemEdit)
      mnuBar.MenuItems.Add(myMenuItemView)
      mnuBar.MenuItems.Add(myMenuItemProject)

     ' defining some sub menus
      Dim myMenuItemNew As New MenuItem("&New")
      Dim myMenuItemOpen As New MenuItem("&Open")
      Dim myMenuItemSave As New MenuItem("&Save")

      'add sub menus to the File menu
      myMenuItemFile.MenuItems.Add(myMenuItemNew)
      myMenuItemFile.MenuItems.Add(myMenuItemOpen)
      myMenuItemFile.MenuItems.Add(myMenuItemSave)

      'add the main menu to the form
      Me.Menu = mnuBar
     
      ' Set the caption bar text of the form.  
      Me.Text = "tutorialspoint.com"
   End Sub
End Class

When the above code is executed and run using Start button available at the Microsoft Visual Studio tool bar, it will show the following window −

Windows Forms contain a rich set of classes for creating your own custom menus with modern appearance, look and feel. The MenuStrip, ToolStripMenuItem, ContextMenuStrip controls are used to create menu bars and context menus efficiently.

Click the following links to check their details −

Adding the Cut, Copy and Paste Functionalities in a Form

The methods exposed by the ClipBoard class are used for adding the cut, copy and paste functionalities in an application. The ClipBoard class provides methods to place data on and retrieve data from the system Clipboard.

It has the following commonly used methods −

Following is an example, which shows how we cut, copy and paste data using methods of the Clipboard class. Take the following steps −

• Add a rich text box control and three button controls on the form.

• Change the text property of the buttons to Cut, Copy and Paste, respectively.

• Double click on the buttons to add the following code in the code editor −

Public Class Form1
   Private Sub Form1_Load(sender As Object, e As EventArgs) _ 
    Handles MyBase.Load
      ' Set the caption bar text of the form.  
      Me.Text = "tutorialspoint.com"
   End Sub
   
   Private Sub Button1_Click(sender As Object, e As EventArgs) _ 
      Handles Button1.Click
      Clipboard.SetDataObject(RichTextBox1.SelectedText)
      RichTextBox1.SelectedText = ""
   End Sub
   
   Private Sub Button2_Click(sender As Object, e As EventArgs) _
       Handles Button2.Click
      Clipboard.SetDataObject(RichTextBox1.SelectedText)
   End Sub
   
   Private Sub Button3_Click(sender As Object, e As EventArgs) _
    Handles Button3.Click
      Dim iData As IDataObject
      iData = Clipboard.GetDataObject()
      If (iData.GetDataPresent(DataFormats.Text)) Then
         RichTextBox1.SelectedText = iData.GetData(DataFormats.Text)
      Else
         RichTextBox1.SelectedText = " "
      End If
   End Sub
End Class

When the above code is executed and run using Start button available at the Microsoft Visual Studio tool bar, it will show the following window −

Enter some text and check how the buttons work.

Anchoring and Docking Controls in a Form

Anchoring allows you to set an anchor position for a control to the edges of its container control, for example, the form. The Anchor property of the Control class allows you to set values of this property. The Anchor property gets or sets the edges of the container to which a control is bound and determines how a control is resized with its parent.

When you anchor a control to a form, the control maintains its distance from the edges of the form and its anchored position, when the form is resized.

You can set the Anchor property values of a control from the Properties window −

For example, let us add a Button control on a form and set its anchor property to Bottom, Right. Run this form to see the original position of the Button control with respect to the form.

Now, when you stretch the form, the distance between the Button and the bottom right corner of the form remains same.

Docking of a control means docking it to one of the edges of its container. In docking, the control fills certain area of the container completely.

The Dock property of the Control class does this. The Dock property gets or sets which control borders are docked to its parent control and determines how a control is resized with its parent.

You can set the Dock property values of a control from the Properties window −

For example, let us add a Button control on a form and set its Dock property to Bottom. Run this form to see the original position of the Button control with respect to the form.

Now, when you stretch the form, the Button resizes itself with the form.

Modal Forms

Modal Forms are those forms that need to be closed or hidden before you can continue working with the rest of the application. All dialog boxes are modal forms. A MessageBox is also a modal form.

You can call a modal form by two ways −

• Calling the ShowDialog method

• Calling the Show method

Let us take up an example in which we will create a modal form, a dialog box. Take the following steps −

• Add a form, Form1 to your application, and add two labels and a button control to Form1

• Change the text properties of the first label and the button to ‘Welcome to Tutorials Point’ and ‘Enter your Name’, respectively. Keep the text properties of the second label as blank.

  

• Add a new Windows Form, Form2, and add two buttons, one label, and a text box to Form2.

• Change the text properties of the buttons to OK and Cancel, respectively. Change the text properties of the label to ‘Enter your name:’.

• Set the FormBorderStyle property of Form2 to FixedDialog, for giving it a dialog box border.

• Set the ControlBox property of Form2 to False.

• Set the ShowInTaskbar property of Form2 to False.

• Set the DialogResult property of the OK button to OK and the Cancel button to Cancel.

Add the following code snippets in the Form2_Load method of Form2 −

Private Sub Form2_Load(sender As Object, e As EventArgs) _
   Handles MyBase.Load
   AcceptButton = Button1
   CancelButton = Button2
End Sub

Add the following code snippets in the Button1_Click method of Form1 −

Private Sub Button1_Click(sender As Object, e As EventArgs) _
   Handles Button1.Click
   Dim frmSecond As Form2 = New Form2()
   
   If frmSecond.ShowDialog() = DialogResult.OK Then
      Label2.Text = frmSecond.TextBox1.Text
   End If
End Sub

When the above code is executed and run using Start button available at the Microsoft Visual Studio tool bar, it will show the following window −

Clicking on the ‘Enter your Name’ button displays the second form −

Clicking on the OK button takes the control and information back from the modal form to the previous form −

VB.Net — Event Handling

Events are basically a user action like key press, clicks, mouse movements, etc., or some occurrence like system generated notifications. Applications need to respond to events when they occur.

Clicking on a button, or entering some text in a text box, or clicking on a menu item, all are examples of events. An event is an action that calls a function or may cause another event. Event handlers are functions that tell how to respond to an event.

VB.Net is an event-driven language. There are mainly two types of events −

• Mouse events

• Keyboard events

Handling Mouse Events

Mouse events occur with mouse movements in forms and controls. Following are the various mouse events related with a Control class −

• MouseDown − it occurs when a mouse button is pressed

• MouseEnter − it occurs when the mouse pointer enters the control

• MouseHover − it occurs when the mouse pointer hovers over the control

• MouseLeave − it occurs when the mouse pointer leaves the control

• MouseMove − it occurs when the mouse pointer moves over the control

• MouseUp − it occurs when the mouse pointer is over the control and the mouse button is released

• MouseWheel − it occurs when the mouse wheel moves and the control has focus

The event handlers of the mouse events get an argument of type MouseEventArgs. The MouseEventArgs object is used for handling mouse events. It has the following properties −

• Buttons − indicates the mouse button pressed

• Clicks − indicates the number of clicks

• Delta − indicates the number of detents the mouse wheel rotated

• X − indicates the x-coordinate of mouse click

• Y − indicates the y-coordinate of mouse click

Example

Following is an example, which shows how to handle mouse events. Take the following steps −

• Add three labels, three text boxes and a button control in the form.

• Change the text properties of the labels to — Customer ID, Name and Address, respectively.

• Change the name properties of the text boxes to txtID, txtName and txtAddress, respectively.

• Change the text property of the button to ‘Submit’.

• Add the following code in the code editor window −

Public Class Form1
   Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
      ' Set the caption bar text of the form.   
      Me.Text = "tutorialspont.com"
   End Sub

   Private Sub txtID_MouseEnter(sender As Object, e As EventArgs)_
      Handles txtID.MouseEnter
      'code for handling mouse enter on ID textbox
      txtID.BackColor = Color.CornflowerBlue
      txtID.ForeColor = Color.White
   End Sub
   
   Private Sub txtID_MouseLeave(sender As Object, e As EventArgs) _
      Handles txtID.MouseLeave
      'code for handling mouse leave on ID textbox
      txtID.BackColor = Color.White
      txtID.ForeColor = Color.Blue
   End Sub
   
   Private Sub txtName_MouseEnter(sender As Object, e As EventArgs) _
      Handles txtName.MouseEnter
      'code for handling mouse enter on Name textbox
      txtName.BackColor = Color.CornflowerBlue
      txtName.ForeColor = Color.White
   End Sub
   
   Private Sub txtName_MouseLeave(sender As Object, e As EventArgs) _
      Handles txtName.MouseLeave
      'code for handling mouse leave on Name textbox
      txtName.BackColor = Color.White
      txtName.ForeColor = Color.Blue
   End Sub
   
   Private Sub txtAddress_MouseEnter(sender As Object, e As EventArgs) _
      Handles txtAddress.MouseEnter
      'code for handling mouse enter on Address textbox
      txtAddress.BackColor = Color.CornflowerBlue
      txtAddress.ForeColor = Color.White
   End Sub
   
   Private Sub txtAddress_MouseLeave(sender As Object, e As EventArgs) _
      Handles txtAddress.MouseLeave
      'code for handling mouse leave on Address textbox
      txtAddress.BackColor = Color.White
      txtAddress.ForeColor = Color.Blue
   End Sub

   Private Sub Button1_Click(sender As Object, e As EventArgs) _
      Handles Button1.Click
      MsgBox("Thank you " & txtName.Text & ", for your kind cooperation")
   End Sub
End Class

When the above code is executed and run using Start button available at the Microsoft Visual Studio tool bar, it will show the following window −

Try to enter text in the text boxes and check the mouse events −

Handling Keyboard Events

Following are the various keyboard events related with a Control class −

• KeyDown − occurs when a key is pressed down and the control has focus

• KeyPress − occurs when a key is pressed and the control has focus

• KeyUp − occurs when a key is released while the control has focus

The event handlers of the KeyDown and KeyUp events get an argument of type KeyEventArgs. This object has the following properties −

• Alt − it indicates whether the ALT key is pressed

• Control − it indicates whether the CTRL key is pressed

• Handled − it indicates whether the event is handled

• KeyCode − stores the keyboard code for the event

• KeyData − stores the keyboard data for the event

• KeyValue − stores the keyboard value for the event

• Modifiers − it indicates which modifier keys (Ctrl, Shift, and/or Alt) are pressed

• Shift − it indicates if the Shift key is pressed

The event handlers of the KeyDown and KeyUp events get an argument of type KeyEventArgs. This object has the following properties −

• Handled − indicates if the KeyPress event is handled

• KeyChar − stores the character corresponding to the key pressed

Example

Let us continue with the previous example to show how to handle keyboard events. The code will verify that the user enters some numbers for his customer ID and age.

• Add a label with text Property as ‘Age’ and add a corresponding text box named txtAge.

• Add the following codes for handling the KeyUP events of the text box txtID.

Private Sub txtID_KeyUP(sender As Object, e As KeyEventArgs) _
   Handles txtID.KeyUp
   
   If (Not Char.IsNumber(ChrW(e.KeyCode))) Then
      MessageBox.Show("Enter numbers for your Customer ID")
      txtID.Text = " "
   End If
End Sub

• Add the following codes for handling the KeyUP events of the text box txtID.

Private Sub txtAge_KeyUP(sender As Object, e As KeyEventArgs) _
   Handles txtAge.KeyUp
   
   If (Not Char.IsNumber(ChrW(e.keyCode))) Then
      MessageBox.Show("Enter numbers for age")
      txtAge.Text = " "
   End If
End Sub

When the above code is executed and run using Start button available at the Microsoft Visual Studio tool bar, it will show the following window −

If you leave the text for age or ID as blank or enter some non-numeric data, it gives a warning message box and clears the respective text −

VB.Net — Regular Expressions

A regular expression is a pattern that could be matched against an input text. The .Net framework provides a regular expression engine that allows such matching. A pattern consists of one or more character literals, operators, or constructs.

Constructs for Defining Regular Expressions

There are various categories of characters, operators, and constructs that lets you to define regular expressions. Click the following links to find these constructs.

• Character escapes

• Character classes

• Anchors

• Grouping constructs

• Quantifiers

• Backreference constructs

• Alternation constructs

• Substitutions

• Miscellaneous constructs

The Regex Class

The Regex class is used for representing a regular expression.

The Regex class has the following commonly used methods −

For the complete list of methods and properties, please consult Microsoft documentation.

Example 1

The following example matches words that start with ‘S’ −

Imports System.Text.RegularExpressions
Module regexProg
   Sub showMatch(ByVal text As String, ByVal expr As String)
      Console.WriteLine("The Expression: " + expr)
      Dim mc As MatchCollection = Regex.Matches(text, expr)
      Dim m As Match
      
      For Each m In mc
         Console.WriteLine(m)
      Next m
   End Sub
   
   Sub Main()
      Dim str As String = "A Thousand Splendid Suns"
      Console.WriteLine("Matching words that start with 'S': ")
      showMatch(str, "bSS*")
      Console.ReadKey()
   End Sub
End Module

When the above code is compiled and executed, it produces the following result −

Matching words that start with 'S':
The Expression: bSS*
Splendid
Suns

Example 2

The following example matches words that start with ‘m’ and ends with ‘e’ −

Imports System.Text.RegularExpressions
Module regexProg
   Sub showMatch(ByVal text As String, ByVal expr As String)
      Console.WriteLine("The Expression: " + expr)
      Dim mc As MatchCollection = Regex.Matches(text, expr)
      Dim m As Match
      
      For Each m In mc
         Console.WriteLine(m)
      Next m
   End Sub
   
   Sub Main()
      Dim str As String = "make a maze and manage to measure it"
      Console.WriteLine("Matching words that start with 'm' and ends with 'e': ")
      showMatch(str, "bmS*eb")
      Console.ReadKey()
   End Sub
End Module

When the above code is compiled and executed, it produces the following result −

Matching words start with 'm' and ends with 'e':
The Expression: bmS*eb
make
maze
manage
measure

Example 3

This example replaces extra white space −

Imports System.Text.RegularExpressions
Module regexProg
   Sub Main()
      Dim input As String = "Hello    World   "
      Dim pattern As String = "\s+"
      Dim replacement As String = " "
      Dim rgx As Regex = New Regex(pattern)
      Dim result As String = rgx.Replace(input, replacement)
      
      Console.WriteLine("Original String: {0}", input)
      Console.WriteLine("Replacement String: {0}", result)
      Console.ReadKey()
   End Sub
End Module

When the above code is compiled and executed, it produces the following result −

Original String: Hello   World   
Replacement String: Hello World   

VB.Net — Database Access

Applications communicate with a database, firstly, to retrieve the data stored there and present it in a user-friendly way, and secondly, to update the database by inserting, modifying and deleting data.

Microsoft ActiveX Data Objects.Net (ADO.Net) is a model, a part of the .Net framework that is used by the .Net applications for retrieving, accessing and updating data.

ADO.Net Object Model

ADO.Net object model is nothing but the structured process flow through various components. The object model can be pictorially described as −

The data residing in a data store or database is retrieved through the data provider. Various components of the data provider retrieve data for the application and update data.

An application accesses data either through a dataset or a data reader.

• Datasets store data in a disconnected cache and the application retrieves data from it.

• Data readers provide data to the application in a read-only and forward-only mode.

Data Provider

A data provider is used for connecting to a database, executing commands and retrieving data, storing it in a dataset, reading the retrieved data and updating the database.

The data provider in ADO.Net consists of the following four objects −

There are following different types of data providers included in ADO.Net

• The .Net Framework data provider for SQL Server — provides access to Microsoft SQL Server.

• The .Net Framework data provider for OLE DB — provides access to data sources exposed by using OLE DB.

• The .Net Framework data provider for ODBC — provides access to data sources exposed by ODBC.

• The .Net Framework data provider for Oracle — provides access to Oracle data source.

• The EntityClient provider — enables accessing data through Entity Data Model (EDM) applications.

DataSet

DataSet is an in-memory representation of data. It is a disconnected, cached set of records that are retrieved from a database. When a connection is established with the database, the data adapter creates a dataset and stores data in it. After the data is retrieved and stored in a dataset, the connection with the database is closed. This is called the ‘disconnected architecture’. The dataset works as a virtual database containing tables, rows, and columns.

The following diagram shows the dataset object model −

The DataSet class is present in the System.Data namespace. The following table describes all the components of DataSet −

Connecting to a Database

The .Net Framework provides two types of Connection classes −

• SqlConnection − designed for connecting to Microsoft SQL Server.

• OleDbConnection − designed for connecting to a wide range of databases, like Microsoft Access and Oracle.

Example 1

We have a table stored in Microsoft SQL Server, named Customers, in a database named testDB. Please consult ‘SQL Server’ tutorial for creating databases and database tables in SQL Server.

Let us connect to this database. Take the following steps −

• Select TOOLS → Connect to Database

• Select a server name and the database name in the Add Connection dialog box.

  M

• Click on the Test Connection button to check if the connection succeeded.

• Add a DataGridView on the form.

• Click on the Choose Data Source combo box.

• Click on the Add Project Data Source link.

• This opens the Data Source Configuration Wizard.

• Select Database as the data source type

• Choose DataSet as the database model.

• Choose the connection already set up.

• Save the connection string.

• Choose the database object, Customers table in our example, and click the Finish button.

• Select the Preview Data link to see the data in the Results grid −

When the application is run using Start button available at the Microsoft Visual Studio tool bar, it will show the following window −

Example 2

In this example, let us access data in a DataGridView control using code. Take the following steps −

• Add a DataGridView control and a button in the form.

• Change the text of the button control to ‘Fill’.

• Double click the button control to add the required code for the Click event of the button, as shown below −

Imports System.Data.SqlClient
Public Class Form1
   Private Sub Form1_Load(sender As Object, e As EventArgs) _
   Handles MyBase.Load
      'TODO: This line of code loads data into the 'TestDBDataSet.CUSTOMERS' table.   
      You can move, or remove it, as needed.
      
      Me.CUSTOMERSTableAdapter.Fill(Me.TestDBDataSet.CUSTOMERS)
      ' Set the caption bar text of the form.   
      Me.Text = "tutorialspoint.com"
   End Sub
   
   Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
      Dim connection As SqlConnection = New sqlconnection()
      connection.ConnectionString = "Data Source=KABIR-DESKTOP; _
         Initial Catalog=testDB;Integrated Security=True"
      connection.Open()
      Dim adp As SqlDataAdapter = New SqlDataAdapter _
      ("select * from Customers", connection)
      Dim ds As DataSet = New DataSet()
      adp.Fill(ds)
      DataGridView1.DataSource = ds.Tables(0)
   End Sub
End Class

• When the above code is executed and run using Start button available at the Microsoft Visual Studio tool bar, it will show the following window −

• Clicking the Fill button displays the table on the data grid view control −

Creating Table, Columns and Rows

We have discussed that the DataSet components like DataTable, DataColumn and DataRow allow us to create tables, columns and rows, respectively.

The following example demonstrates the concept −

Example 3

So far, we have used tables and databases already existing in our computer. In this example, we will create a table, add columns, rows and data into it and display the table using a DataGridView object.

Take the following steps −

• Add a DataGridView control and a button in the form.

• Change the text of the button control to ‘Fill’.

• Add the following code in the code editor.

Public Class Form1
   Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
      ' Set the caption bar text of the form.   
      Me.Text = "tutorialspont.com"
   End Sub
   
   Private Function CreateDataSet() As DataSet
      'creating a DataSet object for tables
      Dim dataset As DataSet = New DataSet()
      ' creating the student table
      Dim Students As DataTable = CreateStudentTable()
      dataset.Tables.Add(Students)
      Return dataset
   End Function
   
   Private Function CreateStudentTable() As DataTable
      Dim Students As DataTable
      Students = New DataTable("Student")
      ' adding columns
      AddNewColumn(Students, "System.Int32", "StudentID")
      AddNewColumn(Students, "System.String", "StudentName")
      AddNewColumn(Students, "System.String", "StudentCity")
      ' adding rows
      AddNewRow(Students, 1, "Zara Ali", "Kolkata")
      AddNewRow(Students, 2, "Shreya Sharma", "Delhi")
      AddNewRow(Students, 3, "Rini Mukherjee", "Hyderabad")
      AddNewRow(Students, 4, "Sunil Dubey", "Bikaner")
      AddNewRow(Students, 5, "Rajat Mishra", "Patna")
      Return Students
   End Function
   
   Private Sub AddNewColumn(ByRef table As DataTable, _ 
   ByVal columnType As String, ByVal columnName As String)
      Dim column As DataColumn = _ 
         table.Columns.Add(columnName, Type.GetType(columnType))
   End Sub

   'adding data into the table
   Private Sub AddNewRow(ByRef table As DataTable, ByRef id As Integer,_
   ByRef name As String, ByRef city As String)
      Dim newrow As DataRow = table.NewRow()
      newrow("StudentID") = id
      newrow("StudentName") = name
      newrow("StudentCity") = city
      table.Rows.Add(newrow)
   End Sub
   
   Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
      Dim ds As New DataSet
      ds = CreateDataSet()
      DataGridView1.DataSource = ds.Tables("Student")
   End Sub
End Class

• When the above code is executed and run using Start button available at the Microsoft Visual Studio tool bar, it will show the following window −

• Clicking the Fill button displays the table on the data grid view control −

VB.Net — Excel Sheet

VB.Net provides support for interoperability between the COM object model of Microsoft Excel 2010 and your application.

To avail this interoperability in your application, you need to import the namespace Microsoft.Office.Interop.Excel in your Windows Form Application.

Creating an Excel Application from VB.Net

Let’s start with creating a Window Forms Application by following the following steps in Microsoft Visual Studio: File → New Project → Windows Forms Applications

Finally, select OK, Microsoft Visual Studio creates your project and displays following Form1.

Insert a Button control Button1 in the form.

Add a reference to Microsoft Excel Object Library to your project. To do this −

• Select Add Reference from the Project Menu.

• On the COM tab, locate Microsoft Excel Object Library and then click Select.

• Click OK.

Double click the code window and populate the Click event of Button1, as shown below.

'  Add the following code snippet on top of Form1.vb
Imports Excel = Microsoft.Office.Interop.Excel
Public Class Form1
   Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
      Dim appXL As Excel.Application
      Dim wbXl As Excel.Workbook
      Dim shXL As Excel.Worksheet
      Dim raXL As Excel.Range
      
      ' Start Excel and get Application object.
      appXL = CreateObject("Excel.Application")
      appXL.Visible = True
      
      ' Add a new workbook.
      wbXl = appXL.Workbooks.Add
      shXL = wbXl.ActiveSheet
      
      ' Add table headers going cell by cell.
      shXL.Cells(1, 1).Value = "First Name"
      shXL.Cells(1, 2).Value = "Last Name"
      shXL.Cells(1, 3).Value = "Full Name"
      shXL.Cells(1, 4).Value = "Specialization"
      
      ' Format A1:D1 as bold, vertical alignment = center.
      With shXL.Range("A1", "D1")
         .Font.Bold = True
         .VerticalAlignment = Excel.XlVAlign.xlVAlignCenter
      End With
      
      ' Create an array to set multiple values at once.
      Dim students(5, 2) As String
      students(0, 0) = "Zara"
      students(0, 1) = "Ali"
      students(1, 0) = "Nuha"
      students(1, 1) = "Ali"
      students(2, 0) = "Arilia"
      students(2, 1) = "RamKumar"
      students(3, 0) = "Rita"
      students(3, 1) = "Jones"
      students(4, 0) = "Umme"
      students(4, 1) = "Ayman"
      
      ' Fill A2:B6 with an array of values (First and Last Names).
      shXL.Range("A2", "B6").Value = students
      
      ' Fill C2:C6 with a relative formula (=A2 & " " & B2).
      raXL = shXL.Range("C2", "C6")
      raXL.Formula = "=A2 & "" "" & B2"
       
      ' Fill D2:D6 values.
      With shXL
         .Cells(2, 4).Value = "Biology"
         .Cells(3, 4).Value = "Mathmematics"
         .Cells(4, 4).Value = "Physics"
         .Cells(5, 4).Value = "Mathmematics"
         .Cells(6, 4).Value = "Arabic"
      End With
      
      ' AutoFit columns A:D.
      raXL = shXL.Range("A1", "D1")
      raXL.EntireColumn.AutoFit()
      
      ' Make sure Excel is visible and give the user control
      ' of Excel's lifetime.
      appXL.Visible = True
      appXL.UserControl = True
      
      ' Release object references.
      raXL = Nothing
      shXL = Nothing
      wbXl = Nothing
      appXL.Quit()
      appXL = Nothing
      Exit Sub
Err_Handler:
      MsgBox(Err.Description, vbCritical, "Error: " & Err.Number)
   End Sub
End Class

When the above code is executed and run using Start button available at the Microsoft Visual Studio tool bar, it will show the following window −

Clicking on the Button would display the following excel sheet. You will be asked to save the workbook.

VB.Net — Send Email

VB.Net allows sending e-mails from your application. The System.Net.Mail namespace contains classes used for sending e-mails to a Simple Mail Transfer Protocol (SMTP) server for delivery.

The following table lists some of these commonly used classes −

The SmtpClient Class

The SmtpClient class allows applications to send e-mail by using the Simple Mail Transfer Protocol (SMTP).

Following are some commonly used properties of the SmtpClient class −

Following are some commonly used methods of the SmtpClient class −

The following example demonstrates how to send mail using the SmtpClient class. Following points are to be noted in this respect −

• You must specify the SMTP host server that you use to send e-mail. The Host and Port properties will be different for different host server. We will be using gmail server.

• You need to give the Credentials for authentication, if required by the SMTP server.

• You should also provide the email address of the sender and the e-mail address or addresses of the recipients using the MailMessage.From and MailMessage.To properties, respectively.

• You should also specify the message content using the MailMessage.Body property.

Example

In this example, let us create a simple application that would send an e-mail. Take the following steps −

• Add three labels, three text boxes and a button control in the form.

• Change the text properties of the labels to — ‘From’, ‘To:’ and ‘Message:’ respectively.

• Change the name properties of the texts to txtFrom, txtTo and txtMessage respectively.

• Change the text property of the button control to ‘Send’

• Add the following code in the code editor.

Imports System.Net.Mail
Public Class Form1
   Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
      ' Set the caption bar text of the form.   
      Me.Text = "tutorialspoint.com"
   End Sub

   Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
      Try
         Dim Smtp_Server As New SmtpClient
         Dim e_mail As New MailMessage()
         Smtp_Server.UseDefaultCredentials = False
         Smtp_Server.Credentials = New Net.NetworkCredential("username@gmail.com", "password")
         Smtp_Server.Port = 587
         Smtp_Server.EnableSsl = True
         Smtp_Server.Host = "smtp.gmail.com"

         e_mail = New MailMessage()
         e_mail.From = New MailAddress(txtFrom.Text)
         e_mail.To.Add(txtTo.Text)
         e_mail.Subject = "Email Sending"
         e_mail.IsBodyHtml = False
         e_mail.Body = txtMessage.Text
         Smtp_Server.Send(e_mail)
         MsgBox("Mail Sent")

      Catch error_t As Exception
         MsgBox(error_t.ToString)
      End Try
   End Sub

• You must provide your gmail address and real password for credentials.

• When the above code is executed and run using Start button available at the Microsoft Visual Studio tool bar, it will show the following window, which you will use to send your e-mails, try it yourself.

VB.Net — XML Processing

The Extensible Markup Language (XML) is a markup language much like HTML or SGML. This is recommended by the World Wide Web Consortium and available as an open standard.

The System.Xml namespace in the .Net Framework contains classes for processing XML documents. Following are some of the commonly used classes in the System.Xml namespace.

XML Parser APIs

The two most basic and broadly used APIs to XML data are the SAX and DOM interfaces.

• Simple API for XML (SAX) − Here, you register callbacks for events of interest and then let the parser proceed through the document. This is useful when your documents are large or you have memory limitations, it parses the file as it reads it from disk, and the entire file is never stored in memory.

• Document Object Model (DOM) API − This is World Wide Web Consortium recommendation wherein the entire file is read into memory and stored in a hierarchical (tree-based) form to represent all the features of an XML document.

SAX obviously can’t process information as fast as DOM can when working with large files. On the other hand, using DOM exclusively can really kill your resources, especially if used on a lot of small files.

SAX is read-only, while DOM allows changes to the XML file. Since these two different APIs literally complement each other there is no reason why you can’t use them both for large projects.

For all our XML code examples, let’s use a simple XML file movies.xml as an input −

<?xml version = "1.0"?>

<collection shelf = "New Arrivals">
   <movie title = "Enemy Behind">
      <type>War, Thriller</type>
      <format>DVD</format>
      <year>2003</year>
      <rating>PG</rating>
      <stars>10</stars>
      <description>Talk about a US-Japan war</description>
   </movie>

   <movie title = "Transformers">
      <type>Anime, Science Fiction</type>
      <format>DVD</format>
      <year>1989</year>
      <rating>R</rating>
      <stars>8</stars>
      <description>A schientific fiction</description>
   </movie>

   <movie title = "Trigun">
      <type>Anime, Action</type>
      <format>DVD</format>
      <episodes>4</episodes>
      <rating>PG</rating>
      <stars>10</stars>
      <description>Vash the Stampede!</description>
   </movie>

   <movie title = "Ishtar">
      <type>Comedy</type>
      <format>VHS</format>
      <rating>PG</rating>
      <stars>2</stars>
      <description>Viewable boredom</description>
   </movie>
</collection>

Parsing XML with SAX API

In SAX model, you use the XmlReader and XmlWriter classes to work with the XML data.

The XmlReader class is used to read XML data in a fast, forward-only and non-cached manner. It reads an XML document or a stream.

Example 1

This example demonstrates reading XML data from the file movies.xml.

Take the following steps −

• Add the movies.xml file in the binDebug folder of your application.

• Import the System.Xml namespace in Form1.vb file.

• Add a label in the form and change its text to ‘Movies Galore’.

• Add three list boxes and three buttons to show the title, type and description of a movie from the xml file.

• Add the following code using the code editor window.

Imports System.Xml
Public Class Form1
   Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
      ' Set the caption bar text of the form.   
      Me.Text = "tutorialspoint.com"
   End Sub
   
   Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
      ListBox1().Items.Clear()
      Dim xr As XmlReader = XmlReader.Create("movies.xml")
      Do While xr.Read()
         If xr.NodeType = XmlNodeType.Element AndAlso xr.Name = "movie" Then
            ListBox1.Items.Add(xr.GetAttribute(0))
         End If
      Loop
   End Sub
   
   Private Sub Button2_Click(sender As Object, e As EventArgs) Handles Button2.Click
      ListBox2().Items.Clear()
      Dim xr As XmlReader = XmlReader.Create("movies.xml")
      Do While xr.Read()
         If xr.NodeType = XmlNodeType.Element AndAlso xr.Name = "type" Then
            ListBox2.Items.Add(xr.ReadElementString)
         Else
            xr.Read()
         End If
      Loop
   End Sub
   
   Private Sub Button3_Click(sender As Object, e As EventArgs) Handles Button3.Click
      ListBox3().Items.Clear()
      Dim xr As XmlReader = XmlReader.Create("movies.xml")
      Do While xr.Read()
         If xr.NodeType = XmlNodeType.Element AndAlso xr.Name = "description" Then
            ListBox3.Items.Add(xr.ReadElementString)
         Else
            xr.Read()
         End If
      Loop
   End Sub
End Class

Execute and run the above code using Start button available at the Microsoft Visual Studio tool bar. Clicking on the buttons would display, title, type and description of the movies from the file.

The XmlWriter class is used to write XML data into a stream, a file or a TextWriter object. It also works in a forward-only, non-cached manner.

Example 2

Let us create an XML file by adding some data at runtime. Take the following steps −

• Add a WebBrowser control and a button control in the form.

• Change the Text property of the button to Show Authors File.

• Add the following code in the code editor.

Imports System.Xml
Public Class Form1
   Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
      ' Set the caption bar text of the form.   
      Me.Text = "tutorialspoint.com"
   End Sub
   Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
      Dim xws As XmlWriterSettings = New XmlWriterSettings()
      xws.Indent = True
      xws.NewLineOnAttributes = True
      Dim xw As XmlWriter = XmlWriter.Create("authors.xml", xws)
      xw.WriteStartDocument()
      xw.WriteStartElement("Authors")
      xw.WriteStartElement("author")
      xw.WriteAttributeString("code", "1")
      xw.WriteElementString("fname", "Zara")
      xw.WriteElementString("lname", "Ali")
      xw.WriteEndElement()
      xw.WriteStartElement("author")
      xw.WriteAttributeString("code", "2")
      xw.WriteElementString("fname", "Priya")
      xw.WriteElementString("lname", "Sharma")
      xw.WriteEndElement()
      xw.WriteStartElement("author")
      xw.WriteAttributeString("code", "3")
      xw.WriteElementString("fname", "Anshuman")
      xw.WriteElementString("lname", "Mohan")
      xw.WriteEndElement()
      xw.WriteStartElement("author")
      xw.WriteAttributeString("code", "4")
      xw.WriteElementString("fname", "Bibhuti")
      xw.WriteElementString("lname", "Banerjee")
      xw.WriteEndElement()
      xw.WriteStartElement("author")
      xw.WriteAttributeString("code", "5")
      xw.WriteElementString("fname", "Riyan")
      xw.WriteElementString("lname", "Sengupta")
      xw.WriteEndElement()
      xw.WriteEndElement()
      xw.WriteEndDocument()
      xw.Flush()
      xw.Close()
      WebBrowser1.Url = New Uri(AppDomain.CurrentDomain.BaseDirectory + "authors.xml")
   End Sub
End Class

• Execute and run the above code using Start button available at the Microsoft Visual Studio tool bar. Clicking on the Show Author File would display the newly created authors.xml file on the web browser.

Parsing XML with DOM API

According to the Document Object Model (DOM), an XML document consists of nodes and attributes of the nodes. The XmlDocument class is used to implement the XML DOM parser of the .Net Framework. It also allows you to modify an existing XML document by inserting, deleting or updating data in the document.

Following are some of the commonly used methods of the XmlDocument class −

Example 3

In this example, let us insert some new nodes in the xml document authors.xml and then show all the authors’ first names in a list box.

Take the following steps −

• Add the authors.xml file in the bin/Debug folder of your application( it should be there if you have tried the last example)

• Import the System.Xml namespace

• Add a list box and a button control in the form and set the text property of the button control to Show Authors.

• Add the following code using the code editor.

Imports System.Xml
Public Class Form1
   Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
      ' Set the caption bar text of the form.   
      Me.Text = "tutorialspoint.com"
   End Sub
   
   Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
      ListBox1.Items.Clear()
      
      Dim xd As XmlDocument = New XmlDocument()
      xd.Load("authors.xml")
      
      Dim newAuthor As XmlElement = xd.CreateElement("author")
      newAuthor.SetAttribute("code", "6")
      
      Dim fn As XmlElement = xd.CreateElement("fname")
      fn.InnerText = "Bikram"
      newAuthor.AppendChild(fn)
      
      Dim ln As XmlElement = xd.CreateElement("lname")
      ln.InnerText = "Seth"
      newAuthor.AppendChild(ln)
      xd.DocumentElement.AppendChild(newAuthor)
      
      Dim tr As XmlTextWriter = New XmlTextWriter("movies.xml", Nothing)
      tr.Formatting = Formatting.Indented
      xd.WriteContentTo(tr)
      tr.Close()
      
      Dim nl As XmlNodeList = xd.GetElementsByTagName("fname")
      
      For Each node As XmlNode In nl
         ListBox1.Items.Add(node.InnerText)
      Next node
   End Sub
End Class

• Execute and run the above code using Start button available at the Microsoft Visual Studio tool bar. Clicking on the Show Author button would display the first names of all the authors including the one we have added at runtime.

VB.Net — Web Programming

A dynamic web application consists of either or both of the following two types of programs −

• Server-side scripting − these are programs executed on a web server, written using server-side scripting languages like ASP (Active Server Pages) or JSP (Java Server Pages).

• Client-side scripting − these are programs executed on the browser, written using scripting languages like JavaScript, VBScript, etc.

ASP.Net is the .Net version of ASP, introduced by Microsoft, for creating dynamic web pages by using server-side scripts. ASP.Net applications are compiled codes written using the extensible and reusable components or objects present in .Net framework. These codes can use the entire hierarchy of classes in .Net framework.

The ASP.Net application codes could be written in either of the following languages −

• Visual Basic .Net

• C#

• Jscript

• J#

In this chapter, we will give a very brief introduction to writing ASP.Net applications using VB.Net. For detailed discussion, please consult the ASP.Net Tutorial.

ASP.Net Built-in Objects

ASP.Net has some built-in objects that run on a web server. These objects have methods, properties and collections that are used in application development.

The following table lists the ASP.Net built-in objects with a brief description −

ASP.Net Programming Model

ASP.Net provides two types of programming models −

• Web Forms − this enables you to create the user interface and the application logic that would be applied to various components of the user interface.

• WCF Services − this enables you to remote access some server-side functionalities.

For this chapter, you need to use Visual Studio Web Developer, which is free. The IDE is almost same as you have already used for creating the Windows Applications.

Web Forms

Web forms consists of −

• User interface

• Application logic

User interface consists of static HTML or XML elements and ASP.Net server controls. When you create a web application, HTML or XML elements and server controls are stored in a file with .aspx extension. This file is also called the page file.

The application logic consists of code applied to the user interface elements in the page. You write this code in any of .Net language like, VB.Net, or C#. The following figure shows a Web Form in Design view −

Example

Let us create a new web site with a web form, which will show the current date and time, when a user clicks a button. Take the following steps −

• Select File → New → Web Site. The New Web Site Dialog Box appears.

• Select the ASP.Net Empty Web Site templates. Type a name for the web site and select a location for saving the files.

• You need to add a Default page to the site. Right click the web site name in the Solution Explorer and select Add New Item option from the context menu. The Add New Item dialog box is displayed −

• Select Web Form option and provide a name for the default page. We have kept it as Default.aspx. Click the Add button.

• The Default page is shown in Source view

• Set the title for the Default web page by adding a value to the <Title> tag of the page, in the Source view −

• To add controls on the web page, go to the design view. Add three labels, a text box and a button on the form.

• Double-click the button and add the following code to the Click event of the button −

Protected Sub Button1_Click(sender As Object, e As EventArgs) _
Handles Button1.Click
   Label2.Visible = True
   Label2.Text = "Welcome to Tutorials Point: " + TextBox1.Text
   Label3.Text = "You visited us at: " + DateTime.Now.ToString()
End Sub

When the above code is executed and run using Start button available at the Microsoft Visual Studio tool bar, the following page opens in the browser −

Enter your name and click on the Submit button −

Web Services

A web service is a web application, which is basically a class consisting of methods that could be used by other applications. It also follows a code-behind architecture like the ASP.Net web pages, although it does not have an user interface.

The previous versions of .Net Framework used this concept of ASP.Net Web Service, which had .asmx file extension. However, from .Net Framework 4.0 onwards, the Windows Communication Foundation (WCF) technology has evolved as the new successor of Web Services, .Net Remoting and some other related technologies. It has rather clubbed all these technologies together. In the next section, we will provide a brief introduction to Windows Communication Foundation(WCF).

If you are using previous versions of .Net Framework, you can still create traditional web services. Please consult ASP.Net — Web Services tutorial for detailed description.

Windows Communication Foundation

Windows Communication Foundation or WCF provides an API for creating distributed service-oriented applications, known as WCF Services.

Like Web services, WCF services also enable communication between applications. However, unlike web services, the communication here is not limited to HTTP only. WCF can be configured to be used over HTTP, TCP, IPC, and Message Queues. Another strong point in favour of WCF is, it provides support for duplex communication, whereas with web services we could achieve simplex communication only.

From beginners’ point of view, writing a WCF service is not altogether so different from writing a Web Service. To keep the things simple, we will see how to −

• Create a WCF Service

• Create a Service Contract and define the operations

• Implement the contract

• Test the Service

• Utilize the Service

Example

To understand the concept let us create a simplistic service that will provide stock price information. The clients can query about the name and price of a stock based on the stock symbol. To keep this example simple, the values are hardcoded in a two-dimensional array. This service will have two methods −

• GetPrice Method − it will return the price of a stock, based on the symbol provided.

• GetName Method − it will return the name of the stock, based on the symbol provided.

Creating a WCF Service

Take the following steps −

• Open VS Express for Web 2012

• Select New Web Site to open the New Web Site dialog box.

• Select WCF Service template from list of templates −

• Select File System from the Web location drop-down list.

• Provide a name and location for the WCF Service and click OK.

• A new WCF Service is created.

Creating a Service Contract and Defining the Operations

A service contract defines the operation that a service performs. In the WCF Service application, you will find two files automatically created in the App_Code folder in the Solution Explorer

• IService.vb − this will have the service contract; in simpler words, it will have the interface for the service, with the definitions of methods the service will provide, which you will implement in your service.

• Service.vb − this will implement the service contract.

• Replace the code of the IService.vb file with the given code −

Public Interface IService
   <OperationContract()>
   Function GetPrice(ByVal symbol As String) As Double

   <OperationContract()>
   Function GetName(ByVal symbol As String) As String
End Interface

Implementing the Contract

In the Service.vb file, you will find a class named Service which will implement the Service Contract defined in the IService interface.

Replace the code of IService.vb with the following code −

' NOTE: You can use the "Rename" command on the context menu to change the class name "Service" in code, svc and config file together.
Public Class Service
   Implements IService
   Public Sub New()
   End Sub
   Dim stocks As String(,) =
   {
      {"RELIND", "Reliance Industries", "1060.15"},
      {"ICICI", "ICICI Bank", "911.55"},
      {"JSW", "JSW Steel", "1201.25"},
      {"WIPRO", "Wipro Limited", "1194.65"},
      {"SATYAM", "Satyam Computers", "91.10"}
   }

   Public Function GetPrice(ByVal symbol As String) As Double _
   Implements IService.GetPrice

      Dim i As Integer
      'it takes the symbol as parameter and returns price
      For i = 0 To i = stocks.GetLength(0) - 1

         If (String.Compare(symbol, stocks(i, 0)) = 0) Then
            Return Convert.ToDouble(stocks(i, 2))
         End If
      Next i
      Return 0
   End Function

   Public Function GetName(ByVal symbol As String) As String _
   Implements IService.GetName

      ' It takes the symbol as parameter and 
      ' returns name of the stock
      Dim i As Integer
      For i = 0 To i = stocks.GetLength(0) - 1

         If (String.Compare(symbol, stocks(i, 0)) = 0) Then
            Return stocks(i, 1)
         End If
      Next i
      Return "Stock Not Found"
   End Function
End Class

Testing the Service

To run the WCF Service, so created, select the Debug → Start Debugging option from the menu bar. The output would be −

For testing the service operations, double click the name of the operation from the tree on the left pane. A new tab will appear on the right pane.

Enter the value of parameters in the Request area of the right pane and click the ‘Invoke’ button.

The following diagram displays the result of testing the GetPrice operation −

The following diagram displays the result of testing the GetName operation −

Utilizing the Service

Let us add a default page, a ASP.NET web form in the same solution from which we will be using the WCF Service we have just created.

Take the following steps −

• Right click on the solution name in the Solution Explorer and add a new web form to the solution. It will be named Default.aspx.

• Add two labels, a text box and a button on the form.

• We need to add a service reference to the WCF service we just created. Right click the website in the Solution Explorer and select Add Service Reference option. This opens the Add Service Reference Dialog box.

• Enter the URL(location) of the Service in the Address text box and click the Go button. It creates a service reference with the default name ServiceReference1. Click the OK button.

Adding the reference does two jobs for your project −

• Creates the Address and Binding for the service in the web.config file.

• Creates a proxy class to access the service.

• Double click the Get Price button in the form, to enter the following code snippet on its Click event −

Partial Class _Default
   Inherits System.Web.UI.Page

   Protected Sub Button1_Click(sender As Object, e As EventArgs) _
   Handles Button1.Click
      Dim ser As ServiceReference1.ServiceClient = _ 
      New ServiceReference1.ServiceClient
      Label2.Text = ser.GetPrice(TextBox1.Text).ToString()
   End Sub
End Class

• When the above code is executed and run using Start button available at the Microsoft Visual Studio tool bar, the following page opens in the browser −

• Enter a symbol and click the Get Price button to get the hard-coded price −

VB.Net – Обзор

Visual Basic .NET (VB.NET) – это объектно-ориентированный язык программирования, реализованный на .NET Framework. Хотя это развитие классического языка Visual Basic, он не имеет обратной совместимости с VB6, и любой код, написанный в старой версии, не компилируется в VB.NET.

Как и все другие языки .NET, VB.NET полностью поддерживает объектно-ориентированные концепции. Все в VB.NET является объектом, включая все примитивные типы (Short, Integer, Long, String, Boolean и т. Д.) И определяемые пользователем типы, события и даже сборки. Все объекты наследуются от базового класса Object.

VB.NET реализован на платформе Microsoft .NET. Следовательно, он имеет полный доступ ко всем библиотекам .Net Framework. Также возможно запускать программы VB.NET в Mono, альтернативе .NET с открытым исходным кодом, не только под Windows, но даже под Linux или Mac OSX.

Следующие причины делают VB.Net широко используемым профессиональным языком –

• Современный, общего назначения.

• Объектно-ориентированный.

• Компонент ориентирован.

• Легко обучаема.

• Структурированный язык.

• Он производит эффективные программы.

• Он может быть скомпилирован на различных компьютерных платформах.

• Часть .Net Framework.

Современный, общего назначения.

Объектно-ориентированный.

Компонент ориентирован.

Легко обучаема.

Структурированный язык.

Он производит эффективные программы.

Он может быть скомпилирован на различных компьютерных платформах.

Часть .Net Framework.

Сильные возможности программирования VB.Net

VB.Net имеет множество сильных функций программирования, которые делают его привлекательным для множества программистов по всему миру. Давайте упомянем некоторые из этих функций –

• Булевы условия

• Автоматическая сборка мусора

• Стандартная библиотека

• Версии сборки

• Свойства и События

• Управление делегатами и мероприятиями

• Простота в использовании Generics

• индексаторы

• Условная компиляция

• Простая многопоточность

Булевы условия

Автоматическая сборка мусора

Стандартная библиотека

Версии сборки

Свойства и События

Управление делегатами и мероприятиями

Простота в использовании Generics

индексаторы

Условная компиляция

Простая многопоточность

VB.Net – Настройка среды

В этой главе мы обсудим инструменты, доступные для создания приложений VB.Net.

Мы уже упоминали, что VB.Net является частью .Net Framework и используется для написания .Net приложений. Поэтому, прежде чем обсуждать доступные инструменты для запуска программы VB.Net, давайте разберемся, как VB.Net относится к платформе .Net.

.Net Framework

.Net Framework – это революционная платформа, которая помогает вам писать приложения следующих типов:

• Приложения для Windows

• Веб-приложения

• Веб-сервисы

Приложения для Windows

Веб-приложения

Веб-сервисы

Приложения .Net Framework являются мультиплатформенными приложениями. Фреймворк спроектирован таким образом, что его можно использовать на любом из следующих языков: Visual Basic, C #, C ++, Jscript и COBOL и т. Д.

Все эти языки могут получить доступ к структуре, а также общаться друг с другом.

.Net Framework состоит из огромной библиотеки кодов, используемых клиентскими языками, такими как VB.Net. Эти языки используют объектно-ориентированную методологию.

Ниже приведены некоторые компоненты .Net Framework –

• Common Language Runtime (CLR)

• Библиотека классов .Net Framework

• Спецификация общего языка

• Система общего типа

• Метаданные и сборки

• Windows Forms

• ASP.Net и ASP.Net AJAX

• ADO.Net

• Windows Workflow Foundation (WF)

• Windows Presentation Foundation

• Windows Communication Foundation (WCF)

• LINQ

Common Language Runtime (CLR)

Библиотека классов .Net Framework

Спецификация общего языка

Система общего типа

Метаданные и сборки

Windows Forms

ASP.Net и ASP.Net AJAX

ADO.Net

Windows Workflow Foundation (WF)

Windows Presentation Foundation

Windows Communication Foundation (WCF)

LINQ

Работы, выполняемые каждым из этих компонентов, см. В разделе ASP.Net – Введение , а сведения о каждом компоненте см. В документации Microsoft.

Интегрированная среда разработки (IDE) для VB.Net

Microsoft предоставляет следующие инструменты разработки для программирования на VB.Net –

• Visual Studio 2010 (VS)

• Visual Basic 2010 Express (VBE)

• Visual Web Developer

Visual Studio 2010 (VS)

Visual Basic 2010 Express (VBE)

Visual Web Developer

Последние два бесплатны. Используя эти инструменты, вы можете писать все виды программ VB.Net от простых приложений командной строки до более сложных приложений. Выпуски Visual Basic Express и Visual Web Developer Express являются урезанными версиями Visual Studio и имеют одинаковый внешний вид. Они сохраняют большинство функций Visual Studio. В этом руководстве мы использовали Visual Basic 2010 Express и Visual Web Developer (для главы по веб-программированию).

Вы можете скачать его здесь . Он автоматически устанавливается на ваш компьютер. Обратите внимание, что вам нужно активное подключение к Интернету для установки экспресс-издания.

Написание программ на VB.Net для Linux или Mac OS

Хотя .NET Framework работает в операционной системе Windows, есть несколько альтернативных версий, которые работают в других операционных системах. Mono – это версия .NET Framework с открытым исходным кодом, включающая компилятор Visual Basic и работающая в нескольких операционных системах, включая различные версии Linux и Mac OS. Самая последняя версия VB 2012.

Заявленная цель Mono состоит не только в том, чтобы иметь возможность запускать кроссплатформенные приложения Microsoft .NET, но и в том, чтобы предлагать разработчикам Linux более совершенные инструменты разработки. Mono может работать на многих операционных системах, включая Android, BSD, iOS, Linux, OS X, Windows, Solaris и UNIX.

VB.Net – Структура программы

Прежде чем изучать основные строительные блоки языка программирования VB.Net, давайте взглянем на минимальную минимальную структуру программы VB.Net, чтобы ее можно было использовать в качестве справочного материала в следующих главах.

Пример Hello World от VB.Net

Программа VB.Net в основном состоит из следующих частей –

• Объявление пространства имен

• Класс или модуль

• Одна или несколько процедур

• переменные

• Основная процедура

• Заявления и выражения

• Комментарии

Объявление пространства имен

Класс или модуль

Одна или несколько процедур

переменные

Основная процедура

Заявления и выражения

Комментарии

Давайте посмотрим на простой код, который будет печатать слова «Hello World» –

Live Demo

Imports System
Module Module1
   'This program will display Hello World 
   Sub Main()
      Console.WriteLine("Hello World")
      Console.ReadKey()
   End Sub
End Module

Hello, World!

Imports System
Public Class Rectangle
   Private length As Double
   Private width As Double

   'Public methods
   Public Sub AcceptDetails()
      length = 4.5
      width = 3.5
   End Sub

   Public Function GetArea() As Double
      GetArea = length * width
   End Function
   Public Sub Display()
      Console.WriteLine("Length: {0}", length)
      Console.WriteLine("Width: {0}", width)
      Console.WriteLine("Area: {0}", GetArea())

   End Sub

   Shared Sub Main()
      Dim r As New Rectangle()
      r.Acceptdetails()
      r.Display()
      Console.ReadLine()
   End Sub
End Class

Length: 4.5
Width: 3.5
Area: 15.75

Dim r As New Rectangle()

Shared Sub Main()
   Dim r As New Rectangle()
   r.Acceptdetails()
   r.Display()
   Console.ReadLine()
End Sub

Module DataTypes
   Sub Main()
      Dim b As Byte
      Dim n As Integer
      Dim si As Single
      Dim d As Double
      Dim da As Date
      Dim c As Char
      Dim s As String
      Dim bl As Boolean
      
      b = 1
      n = 1234567
      si = 0.12345678901234566
      d = 0.12345678901234566
      da = Today
      c = "U"c
      s = "Me"
      
      If ScriptEngine = "VB" Then
         bl = True
      Else
         bl = False
      End If
      
      If bl Then
         'the oath taking
         Console.Write(c & " and," & s & vbCrLf)
         Console.WriteLine("declaring on the day of: {0}", da)
         Console.WriteLine("We will learn VB.Net seriously")
         Console.WriteLine("Lets see what happens to the floating point variables:")
         Console.WriteLine("The Single: {0}, The Double: {1}", si, d)
      End If
      Console.ReadKey()
   End Sub
End Module

U and, Me
declaring on the day of: 12/4/2012 12:00:00 PM
We will learn VB.Net seriously
Lets see what happens to the floating point variables:
The Single:0.1234568, The Double: 0.123456789012346

Module DataTypes
   Sub Main()
      Dim n As Integer
      Dim da As Date
      Dim bl As Boolean = True
      n = 1234567
      da = Today
      
      Console.WriteLine(bl)
      Console.WriteLine(CSByte(bl))
      Console.WriteLine(CStr(bl))
      Console.WriteLine(CStr(da))
      Console.WriteLine(CChar(CChar(CStr(n))))
      Console.WriteLine(CChar(CStr(da)))
      Console.ReadKey()
   End Sub
End Module

True
-1
True
12/4/2012
1
1

[ < attributelist > ] [ accessmodifier ] [[ Shared ] [ Shadows ] | [ Static ]]
[ ReadOnly ] Dim [ WithEvents ] variablelist

variablename[ ( [ boundslist ] ) ] [ As [ New ] datatype ] [ = initializer ]

Dim StudentID As Integer
Dim StudentName As String
Dim Salary As Double
Dim count1, count2 As Integer
Dim status As Boolean
Dim exitButton As New System.Windows.Forms.Button
Dim lastTime, nextTime As Date

variable_name = value;

Dim pi As Double
pi = 3.14159

Dim StudentID As Integer = 100
Dim StudentName As String = "Bill Smith"

Module variablesNdataypes
   Sub Main()
      Dim a As Short
      Dim b As Integer
      Dim c As Double
      
      a = 10
      b = 20
      c = a + b
      Console.WriteLine("a = {0}, b = {1}, c = {2}", a, b, c)
      Console.ReadLine()
   End Sub
End Module

a = 10, b = 20, c = 30

Dim message As String
message = Console.ReadLine

Module variablesNdataypes
   Sub Main()
      Dim message As String
      Console.Write("Enter message: ")
      message = Console.ReadLine
      Console.WriteLine()
      Console.WriteLine("Your Message: {0}", message)
      Console.ReadLine()
   End Sub
End Module

Enter message: Hello World   
Your Message: Hello World

Dim g As Integer = 20

20 = g

[ < attributelist > ] [ accessmodifier ] [ Shadows ] 
Const constantlist

constantname [ As datatype ] = initializer

'The following statements declare constants.'
Const maxval As Long = 4999
Public Const message As String = "HELLO" 
Private Const piValue As Double = 3.1415

Module constantsNenum
   Sub Main()
      Const PI = 3.14149
      Dim radius, area As Single
      radius = 7
      area = PI * radius * radius
      Console.WriteLine("Area = " & Str(area))
      Console.ReadKey()
   End Sub
End Module

Area = 153.933

[ < attributelist > ] [ accessmodifier ]  [ Shadows ] 
Enum enumerationname [ As datatype ] 
   memberlist
End Enum