Mediator in VB.NET

   1:      ' Mediator Design Pattern.

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

   3:      Class MainApp

   4:          ' Entry point into console application.

   5:          Public Shared Sub Main()

   6:              Dim m As New ConcreteMediator()

   7:              Dim c1 As New ConcreteColleague1(m)

   8:              Dim c2 As New ConcreteColleague2(m)

   9:              m.Colleague1 = c1

  10:              m.Colleague2 = c2

  11:              c1.Send("How are you?")

  12:              c2.Send("Fine, thanks")

  13:              ' Wait for user

  14:              Console.ReadKey()

  15:          End Sub

  16:      End Class

  17:   

  18:      ' The 'Mediator' abstract class

  19:      MustInherit Class Mediator

  20:          Public MustOverride Sub Send(message As String, colleague As Colleague)

  21:      End Class

  22:   

  23:      ' The 'ConcreteMediator' class

  24:      Class ConcreteMediator

  25:          Inherits Mediator

  26:          Private _colleague1 As ConcreteColleague1

  27:          Private _colleague2 As ConcreteColleague2

  28:          Public WriteOnly Property Colleague1() As ConcreteColleague1

  29:              Set(value As ConcreteColleague1)

  30:                  _colleague1 = value

  31:              End Set

  32:          End Property

  33:          Public WriteOnly Property Colleague2() As ConcreteColleague2

  34:              Set(value As ConcreteColleague2)

  35:                  _colleague2 = value

  36:              End Set

  37:          End Property

  38:          Public Overrides Sub Send(message As String, colleague As Colleague)

  39:              If colleague Is _colleague1 Then

  40:                  _colleague2.Notify(message)

  41:              Else

  42:                  _colleague1.Notify(message)

  43:              End If

  44:          End Sub

  45:      End Class

  46:   

  47:      ' The 'Colleague' abstract class

  48:      MustInherit Class Colleague

  49:          Protected mediator As Mediator

  50:          ' Constructor

  51:          Public Sub New(mediator As Mediator)

  52:              Me.mediator = mediator

  53:          End Sub

  54:      End Class

  55:   

  56:      ' A 'ConcreteColleague' class

  57:      Class ConcreteColleague1

  58:          Inherits Colleague

  59:          ' Constructor

  60:          Public Sub New(mediator As Mediator)

  61:              MyBase.New(mediator)

  62:          End Sub

  63:          Public Sub Send(message As String)

  64:              mediator.Send(message, Me)

  65:          End Sub

  66:          Public Sub Notify(message As String)

  67:              Console.WriteLine(Convert.ToString("Colleague1 gets message: ") & message)

  68:          End Sub

  69:      End Class

  70:   

  71:      ' A 'ConcreteColleague' class

  72:      Class ConcreteColleague2

  73:          Inherits Colleague

  74:          ' Constructor

  75:          Public Sub New(mediator As Mediator)

  76:              MyBase.New(mediator)

  77:          End Sub

  78:          Public Sub Send(message As String)

  79:              mediator.Send(message, Me)

  80:          End Sub

  81:          Public Sub Notify(message As String)

  82:              Console.WriteLine(Convert.ToString("Colleague2 gets message: ") & message)

  83:          End Sub

  84:      End Class