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Chapter 1. Introduction
With its release for the .NET platform, the Visual Basic language has undergone dramatic changes.

For example:
? The language itself is now fully object-oriented.
? Applications and components written in Visual Basic .NET have full access to the .NET
Framework, an extensive class library that provides system and application services.
? All applications developed using Visual Basic .NET run within a managed runtime environment,
the .NET common language runtime.
In this introduction, I briefly discuss these changes and other changes before showing you three very
simple, but complete, Visual Basic .NET applications.
1.1 What Is the Microsoft .NET Framework?
The .NET Framework encompasses the following:
? A new way to expose operating system and other APIs. For years, the set of Windows functionality that was available to developers and the way that functionality was invoked were dependent on the language environment being used. For example, the Windows operating system provides the ability to create windows (obviously). Yet, the way this feature was invoked from a C++ program was dramatically different from the way it was invoked from a Visual Basic program. With .NET, the way that operating system services are invoked is uniform across all languages (including code embedded in ASP.NET pages).
This portion of .NET is commonly referred to as the .NET Framework class library. ? A new infrastructure for managing application execution. To provide a number of sophisticated new operating-system services?including code-level security, cross-language class inheritance, cross-language type compatibility, and hardware and operating-system independence, among others?Microsoft developed a new runtime environment known as the Common Language Runtime (CLR). The CLR includes the Common Type System (CTS) for cross-language type compatibility and the Common Language Specification (CLS) for ensuring that third-party libraries can be used from all .NET-enabled languages. To support hardware and operating-system independence, Microsoft developed the Microsoft Intermediate Language (MSIL, or just IL). IL is a CPU-independent machine language-style instruction set into which .NET Framework programs are compiled. IL programs are compiled to the actual machine language on the target platform prior to execution (known as just-in-time, or JIT, compiling). IL is never interpreted. ? A new web server paradigm. To support high-capacity web sites, Microsoft has replaced its Active Server Pages (ASP) technology with ASP.NET. While developers who are used to classic ASP will find ASP.NET familiar on the surface, the underlying engine is different, and far more features are supported. One difference, already mentioned in this chapter, is that ASP.NET web page code is now compiled rather than interpreted, greatly increasing execution speed. ? A new focus on distributed-application architecture.Visual Studio .NET provides top-notch
tools for creating and consuming web services -- vendor-independent software services that can be invoked over the Internet. The .NET Framework is designed top to bottom with the Internet in mind. For example,
ADO.NET, the next step in the evolution of Microsoft's vision of "universal data access,"
assumes that applications will work with disconnected data by default. In addition, the 14
ADO.NET classes provide sophisticated XML capabilities, further increasing their usefulness
in a distributed environment.
An understanding of the .NET Framework is essential to developing professional Visual Basic .NET
applications. The .NET Framework is explained in detail in Chapter 3.
What Is Visual Basic .NET?
 

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

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.

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 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 instant 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 object 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.

• Instant Variables - Each object has its unique set of instant variables. An object's state is created by the values assigned to these instant 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