Question

In Actionscript 3 is there any way to determine the precise display object hierarchy an event will traverse through when dispatched from a given object? The object is not necessarily a display object.

Although I could imagine this actually being useful somehow, in my particular case it is a learning exercise. I’m trying to master the event system in flash and have some locations where I’m very curious what path an event will take when I dispatch it.

Answer 1

The answer is sort of. Events aren’t limited to DisplayObjects, and when they are triggered by DisplayObjects, they don’t always follow the same pattern — the Event may very based on what type of DisplayObject and whether the event was triggered programmatically (through dispatchEvent) or natively (by a mouseClick). It may also vary based on whether bubbling is enabled or not and if it is a custom event. A Loader’s complete event, for example, does not make sense to propagate to parent objects, even though Loader is a display object.

If you’re trying to figure out the parents of the object which dispatched an event, then you’ll want something like this:

import flash.events.Event;
import flash.events.MouseEvent;
import flash.display.DisplayObject;
import flash.display.DisplayObjectContainer;
myDispatcher.addEventListener( MouseEvent.CLICK, clickHandler );

function clickHandler( event:MouseEvent ):void
{
    // event.currentTarget is the object which you're listening to.
    // event.target is the object which actually dispatched the event
    // (if you're listening to a MovieClip and a button inside it is clicked,
    // target will refer to the button, currentTarget the MovieClip)
    var ancestry:Vector.<DisplayObjectContainer> = getAncestry( event.currentTarget as DisplayObject );
    // do somethign with all of the parents.

}

// this function takes a DisplayObject and returns all of its ancestor objects 
// all the way to the root as a Vector.
function getAncestry( obj:DisplayObject ):Vector.<DisplayObjectContainer>
{
    var par:Object = obj.parent;
    var ancestry:Vector.<DisplayObjectContainer> = new Vector.<DisplayObjectContainer>();
    while( par )
    {
        par = par.parent;
        ancestry.push( par as DisplayObject );
        if( par == root ) break;//sometimes the root has a parent.
    }
    return ancestry;
}