Checking if a RoutedEvent has any handlers

Posted by AK on Stack Overflow See other posts from Stack Overflow or by AK
Published on 2010-04-26T18:58:09Z Indexed on 2010/04/26 19:03 UTC
Read the original article Hit count: 386

I've got a custom Button class, that always performs the same action when it gets clicked (opening a specific window). I'm adding a Click event that can be assigned in the button's XAML, like a regular button.

When it gets clicked, I want to execute the Click event handler if one has been assigned, otherwise I want to execute the default action. The problem is that there's apparently no way to check if any handlers have been added to an event.

I thought a null check on the event would do it:

if (Click == null) 
{ 
    DefaultClickAction(); 
} 
else 
{ 
    RaiseEvent(new RoutedEventArgs(ClickEvent, this));;
}

...but that doesn't compile. The compiler tells me that I can't do anything other than += or -= to an event outside of the defining class, event though I'm trying to do this check INSIDE the defining class.

I've implemented the correct behavior myself, but it's ugly and verbose and I can't believe there isn't a built-in way to do this. I must be missing something.

Here's the relevant code:

public class MyButtonClass : Control
{
    //...

    public static readonly RoutedEvent ClickEvent =
        EventManager.RegisterRoutedEvent("Click",
                                         RoutingStrategy.Bubble,
                                         typeof(RoutedEventHandler),
                                         typeof(MyButtonClass));

    public event RoutedEventHandler Click
    {
        add { ClickHandlerCount++; AddHandler(ClickEvent, value); }
        remove { ClickHandlerCount--; RemoveHandler(ClickEvent, value); }
    }

    private int ClickHandlerCount = 0;

    private Boolean ClickHandlerExists
    {
        get { return ClickHandlerCount > 0; }
    }

    //...
}

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