How do I handle events with interfaces in VB.NET? - vb.net

Question

I'm new to interfaces and I'm trying to understand how they work.
I wrote the following code, which works properly except the click event which is not firing.
Public Class Form1
Dim WithEvents Button As IClass = New MyButton
Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
Button.Parent = Me
End Sub
Public Sub ClickEventHandler(ByVal Sender As Object, ByVal E As EventArgs) Handles Button.Click
MsgBox("Piwpiw !")
End Sub
End Class
Public Interface IClass
Event Click(ByVal Sender As Object, ByVal E As EventArgs)
Property Parent
End Interface
Public Class MyButton
Inherits SimpleButton
Implements IClass
Public Event click1(ByVal Sender As Object, ByVal E As System.EventArgs) Implements IClass.click
Public Property Parent1 As Object Implements IClass.Parent
Get
Return MyBase.Parent
End Get
Set(ByVal value As Object)
MyBase.Parent = value
End Set
End Property
End Class
What's wrong with that code?
(PS: This is just an example allowing me to understand how interfaces work and doesn't have any functional meaning.)

Answer 1

You're missing a single method in the MyButton class to make this work.
You need this:
Private Sub MyButton_Click(sender As Object, e As System.EventArgs) Handles Me.Click
RaiseEvent click1(sender, e)
End Sub
Essentially SimpleButton already has a click method. It's being raised when you click your derived MyButton class. But the Click event on SimpleButton isn't the same event as Click on the IClass interface. You implemented that as click1. So you just need to raise the click1 method when the Click method is raised. Hence the above method.

Answer 2

In your sample code, I don't see a line where the event is raised. In order to be able to handle an event in the event handler, you'd have a spot in your MyButton class that raises the event, i.e.:
Public Class MyButton
Inherits SimpleButton
Implements IClass
Public Event click1(ByVal Sender As Object, ByVal E As System.EventArgs) Implements IClass.click
Public Property Parent1 As Object Implements IClass.Parent
Get
Return MyBase.Parent
End Get
Set(ByVal value As Object)
MyBase.Parent = value
End Set
End Property
Public Sub SimulateClick()
RaiseEvent click1(Me, New System.EventArgs())
End Sub
End Class
You use the RaiseEvent statement to raise an event.
Above sample, of course, assumes that at some point in your code, you call SimulateClick instead of having a real mouse click (which would involve painting the button and reacting to several mouse events). Once the event is raised, your handler will be called. You could do this from your Form1_Load method:
Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
Button.Parent = Me
Button.SimulateClick()
End Sub
I have noticed that your MyButton class derives from a SimpleButton class. Instead of having the SimulateClick-method, you could also react to a click in the SimpleButton class and place the RaiseEvent statement there.

Answer 3

Here is the solution:
Replace MyButton class with:
Public Class MyButton
Inherits SimpleButton
Implements IClass
Public Shadows Event click(ByVal Sender As Object, ByVal E As System.EventArgs) Implements IClass.Click
Public Property Parent1 As Object Implements IClass.Parent
Get
Return MyBase.Parent
End Get
Set(ByVal value As Object)
MyBase.Parent = value
End Set
End Property
Public Sub ClickEventHandler(ByVal Sender As Object, ByVal E As EventArgs) Handles MyBase.Click
RaiseEvent click(Sender, E)
End Sub
End Class