Recently, I had to have a class that took arguments in its constructor and also was able to dispatch events. Rather than trying to extend EventDispatcher and worry about separating the arguments the rest of the class needed from the ones EventDispatcher needed, I decided to implement IEventDispatcher. Problem was, I hadn't done this in a while, and I couldn't remember the right way to do this and had no idea what project had an example of it. So, I went searching on the web and refreshed my memory that you need to include an EventDispatcher instance in your class and route your IEventDispatcher methods through that object.
I created some boilerplate code that I can just cut and paste to add IEventDispatcher support to a class, and I share it with you now.
//--------------Support for IEventDispatcher--------------//
private var _ed:EventDispatcher;
function addEventListener(type:String, listener:Function,
listener, useCapture, priority, useWeakReference);
Note that you'll need to put an instance of EventDispatcher in _ed in the constructor of the class that's implementing IEventDispatcher:
Josh McDonald posted code that shows how to implement IEventDispatcher with boilerplate that doesn't require adding a line to the constructor.