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Visual Basic.NET Preview

Visual Basic.NET Preview. David Stevenson Consulting Software Engineer, ABB dsteven8@rochester.rr.com. 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

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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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