Friday 11.18.11

Public Delegate Function BinaryOp(ByVal x As Integer, ByVal y As Integer) As Integer

'this class defines the methods that will be "pointed to" by the delegate
Public Class SimpleMath
Public Shared Function Add(ByVal x As Integer, ByVal y As Integer) As Integer
Return x + y
End Function
Public Shared Function Subtract(ByVal x As Integer, ByVal y As Integer) As Integer
Return x - y
End Function
End Class

Module Module1
Sub DisplayDelegateInfo(ByVal delObj As System.Delegate)
For Each d As System.Delegate In delObj.GetInvocationList()
Console.WriteLine("Method Name: {0}", d.Method)
Console.WriteLine("Type name: {0}", d.Target)
Next
End Sub

Sub Main()
Console.WriteLine("***** Simple Delegate Example *****" & vbLf)
'make a delegate object and add a method to the invocation
'liust using the AddressOf keyword
Dim b As BinaryOp = New BinaryOp(AddressOf SimpleMath.Add)

'invoke the method 'pointed to'
Console.WriteLine("10 + 10 is {0}", b(10, 10))
DisplayDelegateInfo(b)
Console.WriteLine()
End Sub

End Module

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Module Module1


Sub Main()
Console.WriteLine("***** Delegates as event enablers *****")
Dim c1 As New Car("SlugBug", 10)

'pass the address of the methods that will be maintained
'by the delegate member variables of the car type
c1.OnAboutToBlow(AddressOf CarAboutToBlow)
c1.OnExploded(AddressOf CarExploded)

Console.WriteLine("***** Speeding Up *****")
For i As Integer = 0 To 5
c1.Accelerate(20)
Next
Console.ReadLine()
End Sub
Public Sub CarAboutToBlow(ByVal msg As String)
Console.WriteLine(msg)
End Sub

Public Sub CarExploded(ByVal msg As String)
Console.WriteLine(msg)
End Sub
End Module

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Module Module1
'declare member variables "WithEvents" to capture the events
Private WithEvents c As New Car("NightRider", 50)

Sub Main()
Console.WriteLine("***** Fun with Events *****")
Dim i As Integer
For i = 0 To 5
c.Accelerate(10)
Next
Console.ReadLine()
End Sub

'event handlers
Public Sub MyExplodedHandler(ByVal s As String) Handles c.Exploded
Console.WriteLine(s)
End Sub

Public Sub MyAboutToDieHandler(ByVal s As String) Handles c.AboutToBlow
Console.WriteLine(s)
End Sub
End Module

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Module Module1
Sub main()
Console.WriteLine("***** Fun with AddHandler/RemoveHandler *****")
'note the lack of WithEvents keyword
Dim c As New Car("NightRider", 50)

'dynamically hook into event using addhandler
AddHandler c.Exploded, AddressOf CarEventHandler
AddHandler c.AboutToBlow, AddressOf CarEventHandler

For I As Integer = 0 To 5
c.Accelerate(10)
Next

Console.ReadLine()

End Sub

Public Sub CarEventHandler(ByVal s As String)
Console.WriteLine(s)
End Sub


End Module

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'this event has been customized
Public Custom Event EngineStart As System.EventHandler
AddHandler(ByVal value As System.EventHandler)
Console.WriteLine("Added connection")
arConnections.Add(value)

End AddHandler

RemoveHandler(ByVal value As System.EventHandler)

End RemoveHandler

RaiseEvent(ByVal sender As Object, ByVal e As System.EventArgs)
For Each h As EventHandler In arConnections
Console.WriteLine("Raising event")
h(sender, e)
Next
End RaiseEvent
End Event

Public Sub Start()
RaiseEvent EngineStart(Me, New EventArgs())
End Sub

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