Testing for the existance of an Event Handler

[malcolm]

Is there a way to test to see if an event handler hasn't already been
added to an event handler listener object? This is what I am doing now
as a hack:

dataView.ListChanged -= new
ListChangedEventHandler(dataView_ListChanged);
dataView.ListChanged += new
ListChangedEventHandler(dataView_ListChanged);
Instead, is there something like:

if (!dataView.ListChanged.Exists("dataView_ListChange d"))
{
dataView.ListChanged += new
ListChangedEventHandler(dataView_ListChanged);
}

thanks,
dave

[Derek Harmon]

"malcolm" <ch********@yahoo.com> wrote in message news:4f**************************@posting.google.c om...

Is there a way to test to see if an event handler hasn't already been
added to an event handler listener object?
public bool IsHandlerAttached( MyEventHandler eh)
{
return ((IList)(MyEvent.GetInvocationList( ))).Contains( eh);
}

However, this functionality must be performed within the class that
exposes MyEvent. Outside of the class, you can't access MyEvent
as if it were a Delegate (which is what it is).
This is what I am doing now as a hack:

dataView.ListChanged -= new
ListChangedEventHandler(dataView_ListChanged);
dataView.ListChanged += new
ListChangedEventHandler(dataView_ListChanged);

Why not just save the EventHandler in a field? Like this,

private ListChangedEventHandler m_notifyListChanged = null;
// . . .
// Attach an event handler.
this.m_notifyListChanged = new ListChangedEventHandler( dataView_ListChanged);
dataView.ListChanged += this.m_notifyListChanged;
// . . .
// Ask yourself if you've attached an event handler.
if ( null != this.m_notifyListChanged )
{
// If so, detach the event handler.
//
dataView.ListChanged -= this.m_notifyListChanged;
this.m_notifyListChanged = null;
}
// . . .
Derek Harmon