public delegate void PreviewMouseEventHandler( object sender, PreviewMouseEventArgs e );
Public Delegate Sub PreviewMouseEventHandler( sender As Object, e As PreviewMouseEventArgs )
When you create a PreviewMouseEventHandler delegate, you identify the method that will handle the event. To associate the event with your event handler, add an instance of the delegate to the event. The event handler is called whenever the event occurs, unless you remove the delegate.