Chain of Resp. in VB.NET

   1:      ' Chain of Responsibility Design Pattern.

   2:      ' See description in //www.vb-net.com/ProgramTheory/ChainOfResp.htm

   3:      Class MainApp

   4:          ' Entry point into console application.

   5:          Public Shared Sub Main()

   6:              ' Setup Chain of Responsibility

   7:              Dim h1 As Handler = New ConcreteHandler1()

   8:              Dim h2 As Handler = New ConcreteHandler2()

   9:              Dim h3 As Handler = New ConcreteHandler3()

  10:              h1.SetSuccessor(h2)

  11:              h2.SetSuccessor(h3)

  12:              ' Generate and process request

  13:              Dim requests As Integer() = {2, 5, 14, 22, 18, 3, 27, 20}

  14:              For Each request As Integer In requests

  15:                  h1.HandleRequest(request)

  16:              Next

  17:              ' Wait for user

  18:              Console.ReadKey()

  19:          End Sub

  20:      End Class

  21:   

  22:      ' The 'Handler' abstract class

  23:      MustInherit Class Handler

  24:          Protected successor As Handler

  25:          Public Sub SetSuccessor(successor As Handler)

  26:              Me.successor = successor

  27:          End Sub

  28:          Public MustOverride Sub HandleRequest(request As Integer)

  29:      End Class

  30:   

  31:      ' The 'ConcreteHandler1' class

  32:      Class ConcreteHandler1

  33:          Inherits Handler

  34:          Public Overrides Sub HandleRequest(request As Integer)

  35:              If request >= 0 AndAlso request < 10 Then

  36:                  Console.WriteLine("{0} handled request {1}", Me.GetType.Name, request)

  37:              ElseIf successor IsNot Nothing Then

  38:                  successor.HandleRequest(request)

  39:              End If

  40:          End Sub

  41:      End Class

  42:   

  43:      ' The 'ConcreteHandler2' class

  44:      Class ConcreteHandler2

  45:          Inherits Handler

  46:          Public Overrides Sub HandleRequest(request As Integer)

  47:              If request >= 10 AndAlso request < 20 Then

  48:                  Console.WriteLine("{0} handled request {1}", Me.GetType.Name, request)

  49:              ElseIf successor IsNot Nothing Then

  50:                  successor.HandleRequest(request)

  51:              End If

  52:          End Sub

  53:      End Class

  54:   

  55:      ' The 'ConcreteHandler3' class

  56:      Class ConcreteHandler3

  57:          Inherits Handler

  58:          Public Overrides Sub HandleRequest(request As Integer)

  59:              If request >= 20 AndAlso request < 30 Then

  60:                  Console.WriteLine("{0} handled request {1}", Me.GetType.Name, request)

  61:              ElseIf successor IsNot Nothing Then

  62:                  successor.HandleRequest(request)

  63:              End If

  64:          End Sub

  65:      End Class