Allowing Users to Handle an event in place of a default event

Question

I am building a custom control and what i would like to do is have an event lets call this event OnMenuShow. Now what i would like to be able to do is handle this event inside my control to show one menu but allow the user implementing my custom control to handle the event in inside the parent form to show a different menu if they wish. so the users code would look something like this.

    Public Sub Control_OnMenuShow(sender as Object, e as CustomEventArgs) handles Control.OnMenyShow
      'DO some work
       e.handled = true
    end Sub

I'm just not sure on how to prevent the event from firing twice once for the code inside the control the other in the event. if someone could point me in the right direction that would be very helpful

-Nathan

Don't write an event handler for your own event. Your control should *only* have a RaiseEvent statement to raise the event. — Hans Passant, Aug 03 '12 at 19:27
Thanks, I can't believe that I didn't think to use a method that raises the event then check if its handled to see if it should go though with the default action or not. Thanks for the help — Risryn, Aug 03 '12 at 20:13

score 0 · Answer 1 · answered Aug 03 '12 at 20:17

In your control:

Public Event MenuShow As EventHandler



Public Overridable Sub OnMenuShow()
  RaiseEvent MenuShow(New EventArgs)
End Sub

Now the consumer may override OnMenuShow which would bypass your raiseevent statement without you needing to "check" anything.

score 0 · Accepted Answer · answered Aug 06 '12 at 15:27

I found that Hans' answer reponse fit my question the best, and had he left it in an answer I would have marked his as answered. I will leave how I ended up coding this for future refrence.

Public Event MenuShow As EventHandler(Of  MenuShowEventArgs)

Public Overridable Sub OnMenuShowEvent()
    Dim args As New MenuShowEventArgs(False, "Control")
    RaiseEvent MenuShow(Me, args)
    if args.handled then return
    'DO WORK
End Sub

Allowing Users to Handle an event in place of a default event

2 Answers2