See my post here on my blog: http://gamesandtech.wordpress.com/2009/10/14/actionscript-3-specifying-events-on-interfaces/

public class MyClass { … }
public interface MyInterface extends MyClass { … }

Will not compile (which is to be expected). However, interfaces can extend other interfaces, in fact, interfaces can extend any number of interfaces.

public interface MyBaseInterface { … }
public interface MyInterface extends IEventDispatcher, MyBaseInterface { … }

So the trick to get your interfaces to have the add/remove even listener methods is rather easy. The trick is to specify which events are part of the interface contract, which is not supported by the language at the moment. Perhaps someone can come up with an approach using Filipe’s method of specifying events at the class level combining interface inheritance.

I myself enjoy the C# approach to events, in fact I wish Actionscript were C# to tell you the truth. I enjoy C# far more than I do AS3, however I enjoy the display list approach Adobe has taken in the Flash world.

I’d suggest C# event handling …

But for now, when I need an interface to define events, I do something like this:

interface ISomeLoader {
function addProgressListener(listener:Function,[whatever]):void;
function removeProgressListener(listener:Function):void;
}
class SomeLoader implements ISomeLoader {
public function addProgressListener(listener:Function,[whatever]):void{
this.addEventListener(MyEvent.PROGRESS, listener);
}
public function removeProgressListener(listener:Function):void{
this.removeEventListener(MyEvent.PROGRESS, listener);
}
}

This doesn’t define the type of event, I specify it in the comments.

Anyway this works fine for me and makes it easier to write the class clients.