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definition - Visual_Basic_.NET

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Visual Basic .NET

                   
Visual Basic .NET
Visual Basic Express icon.png
Paradigm(s) Structured, imperative, object-oriented and declarative
Appeared in 2001
Designed by Microsoft
Developer Microsoft
Stable release 2010 (10.0.30319.1) (12 April 2010; 2 years ago (2010-April-12))
Preview release 11 (11.0.0.0) Windows 8 Developer Preview (29 February 2012; 7 months ago (2012-February-29))
Typing discipline Static, strong, both safe and unsafe,[1] nominative
Major implementations Microsoft Visual Studio, Microsoft Visual Studio Express, SharpDevelop, .NET Framework SDK and Mono
Dialects Microsoft Visual Basic
Influenced by .NET Framework
Platform CLR
OS Chiefly Microsoft Windows
Also on Android, BSD, iOS, Linux, Mac OS X, Solaris and Unix
License Proprietary software (Commercial software or freeware)
Usual filename extensions .vb and .vbs
Website msdn.microsoft.com/en-us/vstudio/hh388568
Screenshot
Microsoft Visual Basic 2010 Express, an integrated development environment that implements Visual Basic .NET.

Visual Basic .NET (VB.NET), is an object-oriented computer programming language that can be viewed as an evolution of the classic Visual Basic (VB), which is implemented on the .NET Framework. Microsoft currently supplies two main editions of IDEs for developing in Visual Basic: Microsoft Visual Studio 2010, which is commercial software and Visual Basic Express Edition 2010, which is free of charge. The command-line compiler, VBC.EXE, is installed as part of the freeware .NET Framework SDK. Mono also includes a command-line VB.NET compiler.

Contents

  Versions

There are 5 versions of Visual Basic .NET implemented by the Visual Basic team.

  Visual Basic .NET (2002) (VB 7.0)

The first version of Visual Basic .NET, which runs on .NET framework 1.0. The most important feature is Managed code, which contrasts with Visual Basic 6.0 and before.

  Visual Basic .NET 2003 (VB 7.1)

Visual Basic .NET 2003 was released with version 1.1 of the .NET Framework. New features included support for the .NET Compact Framework and a better VB upgrade wizard. Improvements were also made to the performance and reliability of the .NET IDE (particularly the background compiler) and runtime. In addition, Visual Basic .NET 2003 was available in the Visual Studio.NET Academic Edition (VS03AE). VS03AE is distributed to a certain number of scholars from each country without cost.

  Visual Basic 2005 (VB 8.0)

Visual Basic 2005 was the name used to refer to Visual Basic .NET, as Microsoft decided to drop the .NET portion of the title.

For this release, Microsoft added many features, including:

  • Edit and Continue
  • Design-time expression evaluation.
  • The My pseudo-namespace (overview, details), which provides:
    • easy access to certain areas of the .NET Framework that otherwise require significant code to access
    • dynamically generated classes (notably My.Forms)
  • Improvements to the VB-to-VB.NET converter[2]
  • The Using keyword, simplifying the use of objects that require the Dispose pattern to free resources
  • Just My Code, which when debugging hides (steps over) boilerplate code written by the Visual Studio .NET IDE and system library code
  • Data Source binding, easing database client/server development

The above functions (particularly My) are intended to reinforce Visual Basic .NET's focus as a rapid application development platform and further differentiate it from C#.

Visual Basic 2005 introduced features meant to bridge the gaps between itself and other "more powerful" .NET languages, adding:

  'IsNot' Operator Patent Application

One other feature of Visual Basic 2005 is the IsNot operator that makes 'If X IsNot Y' equivalent to 'If Not X Is Y, which gained notoriety[5] when it was found to be the subject of a Microsoft patent application.[6][7]

  Visual Basic 2008 (VB 9.0)

Visual Basic 9.0 was released together with the Microsoft .NET Framework 3.5 on 19 November 2007.

For this release, Microsoft added many features, including:

  Visual Basic 2010 (VB 10.0)

In April 2010, Microsoft released Visual Basic 2010. Microsoft had planned to use the Dynamic Language Runtime (DLR) for that release[8] but shifted to a co-evolution strategy between Visual Basic and sister language C# to bring both languages into closer parity with one another. Visual Basic's innate ability to interact dynamically with CLR and COM objects has been enhanced to work with dynamic languages built on the DLR such as IronPython and IronRuby.[9] The Visual Basic compiler was improved to infer line continuation in a set of common contexts, in many cases removing the need for the "_" line continuation character. Also, existing support of inline Functions was complemented with support for inline Subs as well as multi-line versions of both Sub and Function lambdas.[10]

  Relation to older versions of Visual Basic (VB6 and previous)

Whether Visual Basic .NET should be considered as just another version of Visual Basic or a completely different language is a topic of debate. This is not obvious, as once the methods that have been moved around and that can be automatically converted are accounted for, the basic syntax of the language has not seen many "breaking" changes, just additions to support new features like structured exception handling and short-circuited expressions. Two important data type changes occurred with the move to VB.NET. Compared to VB6, the Integer data type has been doubled in length from 16 bits to 32 bits, and the Long data type has been doubled in length from 32 bits to 64 bits. This is true for all versions of VB.NET. A 16-bit integer in all versions of VB.NET is now known as a Short. Similarly, the Windows Forms GUI editor is very similar in style and function to the Visual Basic form editor.

The version numbers used for the new Visual Basic (7, 7.1, 8, 9, ...) clearly imply that it is viewed by Microsoft as still essentially the same product as the old Visual Basic.

The things that have changed significantly are the semantics—from those of an object-based programming language running on a deterministic, reference-counted  engine based on COM to a fully object-oriented language backed by the .NET Framework, which consists of a combination of the Common Language Runtime (a virtual machine using generational garbage collection and a just-in-time compilation engine) and a far larger class library. The increased breadth of the latter is also a problem that VB developers have to deal with when coming to the language, although this is somewhat addressed by the My feature in Visual Studio 2005.

The changes have altered many underlying assumptions about the "right" thing to do with respect to performance and maintainability. Some functions and libraries no longer exist; others are available, but not as efficient as the "native" .NET alternatives. Even if they compile, most converted VB6 applications will require some level of refactoring to take full advantage of the new language. Documentation is available to cover changes in the syntax, debugging applications, deployment and terminology.[11]

  Comparative samples

The following simple example demonstrates similarity in syntax between VB and VB.NET. Both examples pop up a message box saying "Hello, World" with an OK button.

Private Sub Command1_Click()
    MsgBox "Hello, World"
End Sub

A VB.NET example, MsgBox or the MessageBox class can be used:

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
  • Both Visual Basic 6 and Visual Basic .NET will automatically generate the Sub and End Sub statements when the corresponding button is clicked in design view. Visual Basic .NET will also generate the necessary Class and End Class statements. The developer need only add the statement to display the "Hello, World" message box.
  • All procedure calls must be made with parentheses in VB.NET, whereas in VB6 there were different conventions for functions (parentheses required) and subs (no parentheses allowed, unless called using the keyword Call).
  • The names Command1 and Button1 are not obligatory. However, these are default names for a command button in VB6 and VB.NET respectively.
  • In VB.NET, the Handles keyword is used to make the sub Button1_Click a handler for the Click event of the object Button1. In VB6, event handler subs must have a specific name consisting of the object's name ("Command1"), an underscore ("_"), and the event's name ("Click", hence "Command1_Click").
  • There is a function called MsgBox in the Microsoft.VisualBasic namespace which can be used similarly to the corresponding function in VB6. There is a controversy about which function to use as a best practice (not only restricted to showing message boxes but also regarding other features of the Microsoft.VisualBasic namespace). Some programmers prefer to do things "the .NET way", since the Framework classes have more features and are less language-specific. Others argue that using language-specific features makes code more readable (for example, using int (C#) or Integer (VB.NET) instead of System.Int32).
  • In VB 2008, the inclusion of ByVal sender as Object, ByVal e as EventArgs has become optional.

The following example demonstrates a difference between VB6 and VB.NET. Both examples close the active window.

Classic VB Example:

Sub cmdClose_Click()
    Unload Me
End Sub

A VB.NET example:

Sub btnClose_Click(ByVal sender As Object, ByVal e As EventArgs) Handles btnClose{{Not a typo|.}}Click
    Me.Close()
End Sub

The 'cmd' prefix is replaced by the 'btn' prefix, conforming to the new convention previously mentioned.

Visual Basic 6 did not provide common operator shortcuts. The following are equivalent:

VB6 Example:

Sub Timer1_Timer()
    Me.Height = Me.Height - 1
End Sub

VB.NET example:

Sub Timer1_Tick(ByVal sender As Object, ByVal e As EventArgs) Handles Timer1.Tick
    Me.Height -= 1
End Sub

  Criticism

When first introduced, many long-time Visual Basic users complained about Visual Basic .NET because initial versions dropped a large number of language constructs and user interface features that were part of VB6 (which is no longer sold by Microsoft), and changed the semantics of those that remained; for example, in VB.NET parameters are (by default) passed by value, not by reference. Detractors refer pejoratively to VB.NET as Visual Fred or DOTNOT.[12]. One major complaint was that "edit-and-continue", the ability to fix bugs by changing source code in a running program when it is paused at a breakpoint and continue running the code, had been eliminated: this feature was a major productivity aid that had attracted many developers to VB6.

Many of the changes were necessary because they needed to reflect differences between Windows Foundation Classes and equivalent classes in the .NET framework (e.g., for user-interface controls): in addition, certain changed features, such as restricting the scope of local variables to the block where they were declared, and passing parameters by value (which is the only means permitted in Java) make code less error-prone. Reduced risk of error was also the justification for removing features such as computed gosub/goto and the elimination of line numbers (both a legacy of the BASIC language's FORTRAN heritage.) In general, the idea was to make the .NET libraries, rather than language-specific libraries, perform most of the work, so that code written either in VB.NET or C Sharp would compile to almost identical intermediate-code.

However, many of these semantic changes were not backward-compatible with much existing code, and existing code required rewriting and testing, a significant expense when the body of code was non-trivial in size. As author Joel Spolsky noted, "It was the first time a Microsoft upgrade did not respect the work that users did using the previous version of a product." [13]

To Microsoft's credit, Visual Studio supported some degree of automatic translation to VB.NET when VB6 code was pasted into Visual Studio. Also, the VB.NET compiler reported multiple errors (up to a user-specified threshold - e.g., 100 errors) all at once instead of one at a time, with fixes to the source reducing the error list through a process of background compilation. Despite this, adoption of VB.NET was still delayed until 2005, when Microsoft finally reintroduced edit-and-continue: this feature was also made available to C sharp developers.

It is simpler to decompile languages that target Common Intermediate Language (CIL), including VB.NET, compared to languages that compile to machine code. Tools such as .NET Reflector can provide a close approximation to the original code due to the large amount of metadata provided in CIL.[citation needed] This is also true of early versions of Visual Basic (prior to VB5), which could not compile to native code.

Visual Basic 6.0 programs that are mainly algorithmic in nature can be migrated with few difficulties, but certain types of code are more troublesome, namely :

  • Database support: .NET's framework for database access, ADO.NET, emphasizes disconnected operations, which use database-server resources as economically as possible by releasing them when not in use. This results in more scalable code than if the older Data Access Objects or ActiveX Data Objects were used, but the code is also more complex.
  • Graphics: .NET has new (and more powerful) libraries for graphics.
  • Unmanaged operations: .NET, like Java, emphasizes security, so unmanaged code is used only as a last resort.

Other syntactical differences relate to changes made to bring VB.Net into alignment with other .Net languages, such as zero-based arrays (all .Net arrays are 0 to n-1 subscript, whereas classic VB arrays were one-based by default, 1 to n subscript), and structured exception handling (classic VB used a proprietary ON ERROR mechanism); such changes can be difficult or impossible to convert automatically, and converters typically flag such problem areas for manual conversion.

In addition, the required runtime libraries for VB6 programs are provided with Windows 98 SE and above, while VB.NET programs require the installation of the significantly larger .NET Framework. The framework is included with Windows 7, Windows Vista, Windows XP Media Center Edition, Windows XP Tablet PC Edition, Windows Server 2008 and Windows Server 2003. For other supported operating systems such as Windows 2000 or Windows XP (Home or Professional Editions), it must be separately installed.

Microsoft's response to developer dissatisfaction focused around making it easier to move new development and shift existing codebases from VB6 to VB.NET. An offering in 2005 was the VBRun website, offering code samples and articles for:

  • Using VB.NET to complete tasks that were common in VB6, like creating a print preview
  • Integrating VB6 and VB.NET solutions (dubbed VB Fusion)

  Cross-platform and open-source development

The creation of open-source tools for VB.NET development have been slow compared to C#, although the Mono development platform provides an implementation of VB.NET-specific libraries and a VB.NET 8.0 compatible compiler written in VB.NET,[14] as well as standard framework libraries such as Windows Forms GUI library.

SharpDevelop and MonoDevelop are open-source alternative IDEs.

  Examples

The following is a very simple VB.NET program, a version of the classic "Hello world" example created as a console application:

Module Module1
 
    Sub Main()
        Console.WriteLine("Hello, world!")
    End Sub
 
End Module

The effect is to write the text Hello, world! to the command line. Each line serves a specific purpose, as follows:

Module Module1

This is a module definition, a division of code similar to a class, although modules can contain classes. Modules serve as containers of code that can be referenced from other parts of a program.[15]
It is common practice for a module and the code file, which contains it, to have the same name; however, this is not required, as a single code file may contain more than one module and/or class definition.

Sub Main()

This is the entry point where the program begins execution.[16] Sub is an abbreviation of "subroutine."

Console.WriteLine("Hello, world!")

This line performs the actual task of writing the output. Console is a system object, representing a command-line interface and granting programmatic access to the operating system's standard streams. The program calls the Console method WriteLine, which causes the string passed to it to be displayed on the console. Another common method is using MsgBox (a Message Box).[17]

This piece of code is a solution to Floyd's Triangle:

Imports System{{Not a typo|.}}Console
 
Module Program
 
    Sub Main() 
        Dim rows As Integer
 
        ' Input validation.
        Do Until Integer.TryParse(ReadLine("Enter a value for how many rows to be displayed: "),
rows) AndAlso rows >= 1 
            WriteLine("Allowed range is 1 and {0}", Integer.MaxValue) 
        Loop
 
        ' Output of Floyd's Triangle
        Dim current = 1
 
        For row = 1 To rows
            For column = 1 To row 
                Write("{0,-2} ", current) 
                current += 1
            Next
 
            WriteLine()
        Next 
    End Sub
 
    ''' <summary>
    ''' Shadows Console.ReadLine with a version which takes a prompt string.
    ''' </summary>    
    Function ReadLine(Optional prompt As String = Nothing) As String
        If prompt IsNot Nothing Then
            Write(prompt)
        End If
 
        Return Console.ReadLine()
    End Function 
 
End Module

  See also

  References

  1. ^ Option Strict can be used to switch between safe and unsafe type checking.
  2. ^ What's New with the Visual Basic Upgrade Wizard in Visual Basic 2005
  3. ^ Defining and Using Generics in Visual Basic 2005
  4. ^ Operator Overloading in Visual Basic 2005
  5. ^ Sherriff, Lucy (22 February 2005). "Real Software slams MS IsNot patent application". The Register. http://www.theregister.co.uk/2005/02/22/real_slams_ms_patent/. Retrieved 6 April 2009. 
  6. ^ Taft, Darryl K. (21 February 2005). "Real Software Slams Microsofts Patent Effort". eWeek. http://www.eweek.com/article2/0,1759,1766949,00.asp. Retrieved 6 April 2009. 
  7. ^ Vick, Paul A. Jr.; Barsan, Costica Corneliu; Silver, Amanda K. (14 May 2003). "United States Patent Application: 20040230959". IS NOT OPERATOR. US Patent & Trademark Office. http://appft1.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PG01&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.html&r=1&f=G&l=50&s1=%2220040230959%22.PGNR.&OS=DN/20040230959&RS=DN/20040230959. Retrieved 6 April 2009. 
  8. ^ "What the heck is "VBx"?". 1 May 2007. http://www.panopticoncentral.net/archive/2007/05/01/20383.aspx. Retrieved 12 August 2009. "With the new DLR, we have support for IronPython, IronRuby, Javascript, and the new dynamic VBx compile" 
  9. ^ "What's New in Visual Basic 2010". Microsoft. 2009. http://msdn.microsoft.com/en-us/library/we86c8x2%28VS.100%29.aspx. Retrieved 12 August 2009. "Visual Basic binds to objects from dynamic languages such as IronPython and IronRuby" 
  10. ^ "What's New in Visual Basic 2010". Microsoft. 2010. http://msdn.microsoft.com/en-us/vbasic/ee336123.aspx. Retrieved 1 August 2010. 
  11. ^ Migration - Upgrading from Visual Basic 6.0 MSDN – Developer Center – Visual Basic 6.0 Resource Center – Migration –
  12. ^ Karl E. Peterson. "Microsoft Basic: 1976–2001,R.I.P.". http://vb.mvps.org. http://vb.mvps.org/vfred/Trust.asp. Retrieved 7 March 2009. 
  13. ^ Joel Spolsky, How Microsoft Lost the API War, Joel on Software, 13 June 2004, URL: http://www.joelonsoftware.com/articles/APIWar.html
  14. ^ Mono Project: VisualBasic.NET support
  15. ^ "Module Statement". MSDN - Developer Center. http://msdn.microsoft.com/en-us/library/aaxss7da(VS.80).aspx. Retrieved 20 January 2010. 
  16. ^ "Main Procedure in Visual Basic". MSDN - Developer Center. http://msdn.microsoft.com/en-us/library/ms235406(VS.80).aspx. Retrieved 20 January 2010. 
  17. ^ "Visual Basic Version of Hello, World". MSDN - Developer Center. http://msdn.microsoft.com/en-us/library/3cf7t4xt(VS.80).aspx. Retrieved 20 January 2010. 

  Further reading

  External links

   
               

 

All translations of Visual_Basic_.NET


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