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Visual Basic.NET Preview

This guide provides an overview of Visual Basic .NET, covering its installation requirements, features, and programming paradigms such as Object-Oriented Programming (OOP). It highlights its goals in rapid application development, language interoperability, and improved object-oriented features. Key programming concepts like inheritance, encapsulation, polymorphism, and structured exception handling are discussed. Additionally, the article outlines useful examples and syntax changes compared to previous versions, ensuring developers can effectively leverage VB.NET for enterprise web applications.

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Visual Basic.NET Preview

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  1. Visual Basic.NET Preview David StevensonConsulting Software Engineer, ABBdsteven8@rochester.rr.com

  2. How to Get Visual Basic.NET • Requires Windows 2000, IE 5.5 (helpful to install IIS 5 on Win2K Pro) • NET Overview: msdn.microsoft.com/net • Download NET: http://msdn.microsoft.com/downloads/default.asp?URL=/code/sample.asp?url=/msdn-files/027/000/976/msdncompositedoc.xml

  3. Visual Basic.NET Goals • Rapid Application Development of Enterprise Web Applications • Language Interoperability • Improved Object Oriented Features

  4. Modern Language Features • Free Threading • Structured Exception Handling • Type Safety • Shared Members • Initializers

  5. Object Oriented Features • Inheritance • Encapsulation • Overloading • Polymorphism • Parameterized Constructors

  6. Disclaimer • Syntax subject to change in released product. • Most of the following is a summary of Microsoft’s article: Visual Studio Enables the Programmable Web. Examples may be changed slightly.

  7. OOP: Inheritance • Ability to reuse code via Inherits keyword. • Derived class inherits all methods and properties of the base class. • Derived class can override methods defined in the base class using the Overrides keyword. • The derived class can extend the base class by adding new methods and properties.

  8. Inheritance Example Public Class MyBaseClass Function GetCustomer () Console.WriteLine ( "MyBaseClass.GetCustomer" ) End Function End Class Public Class MyDerivedClass : Inherits MyBaseClass Function GetOrders () ... End Function End Class Public Module modmain Sub Main() Dim d As MyDerivedClass d.GetOrders () End Sub End Module

  9. Overrides Example Class MyVeryDerivedClass Inherits MyDerivedClass Overrides Function GetOrders ( )

  10. OOP: Encapsulation • New Protected keyword. • Hides properties/methods except for derived classes. Protected cName as string Protected Function ChangeName ( NewName ) Me.cName = NewName End Function

  11. OOP: Overloading • VB6: Overloading via Implicit Auto-Conversion was potentially dangerous. • VB.NET: Creating two or more functions with the same name, but with different function signatures (parameters). • Overloaded functions can process data differently.

  12. Overloading Example Overloads Sub Display ( theChar As Char ) … Overloads Sub Display ( theInteger As Integer ) … Overloads Sub Display ( theString As String ) …

  13. OOP: Polymorphism • Ability to process an object differently depending on its data type or class. • Ability to redefine methods for derived classes.

  14. Polymorphism Example Class Employee Overridable Function PayEmployee () As Decimal PayEmployee = Hours * HourlyRate End Function End Class Class CommissionedEmployee Inherits Employee Overrides Function PayEmployee ( ) As Decimal PayEmployee = BasePay + Commissions End Function End Class

  15. OOP: Parameterized Constructors • VB6: Unparameterized Class_Initialize • VB.NET: Allows the creation of a new instance of a class while passing arguments for initializing the data of the new class. • VB.NET: Simultaneous creation and initialization of an object instance.

  16. OOP: Parameterized Constructors Public Class Test Private i as Integer Overloads Public Sub New() MyBase.New i = 321 End Sub Overloads Public Sub New ( ByVal par as Integer ) MyClass.New() i = Par End Sub End Class

  17. Interfaces • Abstract classes without implementation. • Can inherit from other interfaces. • Concrete classes can singly inherit, but have multiple interface implementations.

  18. Interface Example Part 1 Public Interface IDog Function Barks ( ByVal strBark As String ) End Interface Public Interface IDog2 : Inherits IDog Function Bites ( ByVal intNumBites As Integer ) End Interface

  19. Interface Example Part 2 Public Class Dogs Implements IDog Implements IDog2 Public Function Bites ( ByVal intNumBites As Integer ) _ Implements IDog2.Bites Console.WriteLine ( "is worse than {0} bites.", intNumBites ) End Function Public Function Barks ( ByVal strBark As String ) _ Implements IDog.Barks Console.Write ( "A Dog's bark {0} ", strBark ) End Function End Class

  20. Free Threading • Concurrent processing improves scalability. • Can start a thread and run asynchronously.

  21. Free Threading Example Sub CreateMyThread ( ) Dim b As BackGroundWork Dim t As Thread Dim b = New BackGroundWork () Set t = New Thread ( New ThreadStart ( AddressOf b.DoIt ) End Sub Class BackGroundWork Sub DoIt ( ) … End Sub End Class

  22. Structured Exception Handling • VB6: On Error Goto • Problem: Goto Error Handling routine, Goto Central Error Processing Routine, Exit out of procedure. • VB.NET: Try… Catch… Finally

  23. Structured Exception Handling Example Sub SEH ( ) Try Open “TESTFILE” For Output As #1 Write #1, CustomerInformation Catch Kill “TESTFILE” Finally Close #1 End try

  24. Try, Catch, Finally Syntax Try tryStatements Catch exception1 [ As type ] [ When expression ] catchStatements [ Exit Try ] Catch exception2 [ As type ] [ When expression ] catchStatements [ Exit Try ] Finally finallyStatements End Try

  25. Type Safety • VB6: Implicit Auto-Conversion on subroutine/function calls. Fails during run-time if data loss occurs. • VB.NET: Option Strict generates compile-time errors if a conversion is required.Option Strict Off.

  26. Data Type Changes • Decimal data type replaces Currency data type. • Long is 64 bits. Integer is 32 bits. Short (new) is 16 bits.

  27. Shared Members • Data and method members of classes that are shared by all instances of a class. • A shared data member is one that all instances of a class share. • A shared method is a method that is not implicitly passed an instance of the class. (consequently, access to class data members is not allowed).

  28. Initializers • Initialization of variables on the lines they are declared. Dim X As Integer = 1 • Equivalent to: Dim X As Integer X = 1 • VB6 Recommendation: Dim X As Integer : X = 1

  29. Namespaces • For organizing code hierarchically. • Example: Namespace UserGroups.NewYork.Rochester.VDUNY ... Insert your code here End Namespace

  30. Namespaces • Always public. • Components within the namespace may have Public, Friend or Private access. • Default access type is Friend. • Private members of a namespace are accessible only within the namespace declaration they were declared in.

  31. Imports Statement • Imports namespace names from referenced projects and assemblies. • Syntax: Imports [aliasname = ] namespace Imports System Imports Microsoft.VisualBasic

  32. Common Language Run-Time • System.* • “This changes everything.” Dodge Intrepid Commerical

  33. Hello World! ' Allow easy reference System namespace classes Imports System ' Module houses the application’s entry point Public Module modmain ' "Main" is application's entry point Sub Main() ' Write text to the console Console.WriteLine ("Hello World using Visual Basic!") End Sub End Module

  34. Migrating from VB6 or VBScript to VB.NET • Following information from A Preview of Active Server Pages+, Appendix B, Moving from VBScript or VB6 to VB7 • Set and Let keywords no longer supported in VB.NET. • Set objVar = objRef ‘ VB6 • objVar = objRef ‘ VB.NET • Class property syntax changes in VB.NET.

  35. VB 6 Class Property Syntax Private mstrString As String Public Property Let MyString ( ByVal NewVal As String ) mstrString = NewVal End Property Public Property Get MyString () As String MyString = mstrString End Property

  36. VB.NET Class Property Syntax Private mstrString As String Public Property MyString As String Get MyString = mstrString End Get Set mstrString = Value End Set End Property

  37. ReadOnly and WriteOnly Properties in VB.NET Private mstrReadOnlyString As String ReadOnly Public Property MyReadOnlyString As String Get MyReadOnlyString = mstrReadOnlyString End Get End Property

  38. Method, Function and Subroutine Calls Require Parenthesis • VB.NET requires parenthesis around method, function and subroutine call parameters. MyFunction ( “Param1”, 1234 ) objRef.MyMethod ( “Param1”, “Param2” ) Response.Write ( “<B>Some Text</B>” ) • VB6: Use: Call MyFunction ( “par1” )

  39. Parameters Default to ByVal • VB.NET defaults to ByVal for all parameters that are intrinsic data types. • Previously(VB6), the default was ByRef. • VB6 Recommendation: Explicitly declare all parameters to ByVal or ByRef. • References to objects, interfaces, array and string variables still default to ByRef.

  40. Declarations in VB.NET • Variables declared in the same statements must be the same type. No longer allowed:Dim a As Integer, b As String • Variables can be initialized in the same statement they are declared:Dim a As Integer = 123Dim intArray ( 3 ) = ( 12, 34, 56 )

  41. Default Values andOptional Parameters • Default values can be supplied in function parameters.Sub MySubr ( ByVal intParam1 As Integer = 123 ) • Optional parameters must always supply a default value.Function MyFunction ( Optional ByVal strParam As String = “MyString” ) • IsMissing keyword is no longer supported.

  42. Explicit Casting Now Required • VB6 Sometimes did implicit auto-conversion of data types. • VB.NET now requires explicit casting.Response.Write ( CStr ( intLoop ) ) Trace.Write ( CStr ( intLoop ) )

  43. Shorthand assignments • VB6: intVar = intVar + 1 • VB.NET: intVar += 1 intVar -= 1 intVar *= 2intVar /= 2

  44. Short Circuited Conditional Statements • Conditional expressions with And or Or: if first test fails, following expressions won’t be executed:if ( a = b ) And ( c = d ) Then …If a is not equal to b, then the test for c = d will not be executed.

  45. References • Visual Studio Enables the Programmable Web, http://msdn.microsoft.com/vstudio/nextgen/technology/language.asp • Joshua Trupin, The Future of Visual Basic: Web Forms, Web Services, and Language Enhancements Slated for Next Generation,http://msdn.microsoft.com/msdnmag/issues/0400/vbnexgen/vbnexgen.asp

  46. References • Introducing Win Forms, http://msdn.microsoft.com/vstudio/nextgen/technology/winforms.asp • Visual Studio Enables the Programmable WebWeb Forms,http://msdn.microsoft.com/vstudio/nextgen/technology/webforms.asp

  47. References • Richard Anderson, Alex Homer, Rob Howard, Dave Sussman, A Preview of Active Server Pages +, Appendix B, Moving from VBScript or VB6 to VB7.

  48. Resources • Microsoft .NET & ASP+ Resources and Information, http://www.devx.com/dotnet/resources/ • News Server: news.devx.comNews Group: vb.vb7 • News Server: msnews.microsoft.comNews Group: microsoft.public.net.*

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