Question

I am using AddHandler to wire a function to a control’s event that I dynamically create:

Public Delegate Sub MyEventHandlerDelegate(ByVal sender As Object, ByVal e As System.EventArgs)

Public Sub BuildControl(EventHandler as System.Delegate)

         dim objMyButton as new button

         AddHandler objMyButton.Click, EventHandler

    end Sub

This code is generating a run-time exception stating:

Unable to cast object of type ‘MyEventHandlerDelegate’ to type ‘System.EventHandler’

What am I not understanding about System.Delegate even though AddHandler takes as an argument of type “System.Delegate”? What Type does “EventHandler need to be to cast to a type that AddHandler can accept? Thanks for your help!

Answer 1

It sounds like the problem is that you are mixing types. The click event requires a System.EventHandler. Your custom delegate, although it has the same signature as System.EventHandler, is not a System.EventHandler.

So, you need to change your method take System.EventHandler instead of System.Delegate:

Public Sub BuildControl(EventHandler as System.EventHandler)
     dim objMyButton as new button
     AddHandler objMyButton.Click, EventHandler
End Sub