Can an Event Handler Remove Itself

Question

I want to limit a mouse event to be handled only once. I assign the event handler by responding to a Button Click:

Private Sub PreparePoint(sender As Object, e As RoutedEventArgs) Handles btnPoint.Click
    AddHandler Map.MouseLeftButtonDown, AddressOf FinishPoint
    .....
End Sub

and try to remove it as follows:

Private Sub FinishPoint(sender As Object, e As MouseButtonEventArgs)
    e.Handled = True
    RemoveHandler Map.MouseDown, AddressOf FinishPoint
    .....
End Sub

However, the event handler is not removed so I infer that my approach is not possible. Is that inference correct and, if so, how can I limit the mouse event to only one occurrence?

Answer 1

Hi Roger,
it works fine. Try following demo:

  <StackPanel>
    <Button x:Name="btn" Content="Click me"/>
  </StackPanel>

And CodeBehind:

Public Class Window1

  Private Sub Window_Loaded(sender As Object, e As RoutedEventArgs)
    AddHandler Me.btn.Click, AddressOf Btn_Click
  End Sub

  Private Sub Btn_Click(sender As Object, e As RoutedEventArgs)
    MessageBox.Show("Click Event")
    RemoveHandler Me.btn.Click, AddressOf Btn_Click
  End Sub

End Class