Shadowing an event handler

I have a two windows forms classes, a base class and a derived class. The base class has an event handler which handles ValueChanged on some component. I have also written a different event handler for the same event on the derived class.

When I create an instance of the derived class and fire the event, I find that both event handlers run (the base class one and then the derived class one). But I want only the handler in the derived class to run.

Is this possible and if so how do I do it?

(This is .NET 3.5) Thanks!

Edit: Here is what the code looks like (can't post the actual code):

Public Class BaseForm
    Inherits System.Windows.Forms.UserControl

(Windows Form Designer Generated Code)

    Private WithEvents myControl As New SomeOtherControl
    Protected value As String

    Private Sub my开发者_C百科Control_ValueChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles myControl.ValueChanged
        value = SomeLogic()
    End Sub
End Class  


Public Class DerivedForm
    Inherits BaseForm

    Private WithEvents myControl As New SomeOtherControl

    Private Sub myControl_ValueChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles myControl.ValueChanged
        value = myControl.Value
    End Sub
End Class

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You can attach multiple handlers to one event so what you are seeing is by design (you have two handlers attached to the same event so they both fire).

That being said there are ways to accomplish what you are trying to do. One way is to move the code out of your base class handler into an overridable method, and then in the derived class override the method. So your base class handler only has 1 line of code,calling the new method you made. If you inherit from the class it will call your overridden method instead.

Public Class BaseForm
    Private Sub myControl_ValueChanged() Handles myControl.ValueChanged
        DoSomeLogic()
    End Sub
    Protected Overridable Sub DoSomeLogic()
    'original logic here
    End Sub
End Class  

Public Class ChildForm
    Inherits BaseForm
    Protected Overrides Sub DoSomeLogic()
    'other logic here
    End Sub

End Class

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I don't believe you can control that.

If it were me, I think I'd intercept the event in the base class, as you are doing, then define ANOTHER event from the base class and raise that event FROM the event handler in the base class.

on return, if the event was handled (presumably by your derived class), then just exit the base event handler, otherwise, proceed with the base event handling.