Question

I have a custom behavior inside a DataTemplate, which raises a custom Routed Event. I want to handle that event with a TriggerAction (send a message, invoke a command, etc).

<Border Background="#01FFFFFF" VerticalAlignment="Center">
             <i:Interaction.Behaviors>
                   <Behaviors:MyBehavior>
                        <i:Interaction.Triggers>
                             <i:EventTrigger EventName="MyEvent">
                                    <triggers:SendMessageAction Parameter="ActionTaskAssign" MessageToken="ActionTask" />
                             </i:CustomEventTrigger>
                        </i:Interaction.Triggers>
                    </Behaviors:DropBehavior>
              </i:Interaction.Behaviors>
<!-- .... -->

Yet I can clearly tell, the EventTrigger is NOT subscribing to the behavior’s MyEvent.

• I’ve tried setting the SourceObject from binding (seen here) but ElementName binding doesn’t seem to work, and neither does FindAncestor
• I’ve tried inheriting from EventTrigger and setting the SourceObject in code, all I got was a StackOverflowException
• I’ve tried writing a custom EventTrigger, but I either write one for every custom event (if all hell breaks loose, I will), or I have to figure out a generic way to handle non-generic RoutedEventHandlers…

What should I do?

Answer 1

The problem is that the EventTrigger doesn’t hook up to the Behavior’s events. Instead it is hooking up to the Behavior’s AssociatedObject’s events. Here is the relevant source code:

protected override void OnAttached()
{
    base.OnAttached();
    DependencyObject associatedObject = base.AssociatedObject;
    Behavior behavior = associatedObject as Behavior;
    FrameworkElement element = associatedObject as FrameworkElement;
    this.RegisterSourceChanged();
    if (behavior != null)
    {
        associatedObject = ((IAttachedObject) behavior).AssociatedObject;
        behavior.AssociatedObjectChanged += new EventHandler(this.OnBehaviorHostChanged);
    }
    ....

}

A related question was asked here :
Handle MouseDragElementBehavior.Dragging event with void Foo() in VM

I solved this myself with writing my own custom behavior that fires off a command (which I needed rather then your message.

You can see my approach in the answer here :

Custom behavior with command