Question

I have learned this method of passing values with addEventLister. Here is the code:

for (var i:uint = 0; i < asteroids.length; i++)
{

     asteroids[i].x = Math.random() * 450;
     asteroids[i].y = Math.random() * 450;
     asteroids[i].addEventListener(MouseEvent.MOUSE_UP, function(e:MouseEvent){
         changeValue(e, otherArguments);
     });

}



public function changeValue(event:MouseEvent, otherArguments:Object):void
{

    playSound(anote);
    trace(event.currentTarget);

}

but there is no explanation about how to remove the event listener from

  asteroids[i].addEventListener(MouseEvent.MOUSE_UP, function(e:MouseEvent){
     changeValue(e, otherArguments);
 });

Answer 1

That is because you cannot unhook an anonymous function if you don’t have a reference to it. If you’d like, you can always keep a reference around:

asteroidsMouseUpHandler = function(e:MouseEvent){
    changeValue(e, otherArguments);
};

asteroids[i].addEventListener(MouseEvent.MOUSE_UP, asteroidsMouseUpHandler);

asteroids[i].removeEventListener(MouseEvent.MOUSE_UP, asteroidsMouseUpHandler);

Of course, if these things are happening in separate member functions, then you need to define a member variable (var asteroidsMouseUpHandler:Function). At that point, you might just want to create it as a named function instead. You’d also only want to do this once (not in a loop) to avoid clobbering your reference. Really, I am showing this code for illustrative purposes only.

Thinking about this further, you might be doing this because the otherArguments is specific to the particular asteroids[i] instance so that you are actually creating a new anonymous function every time you hook it. In that case, if that is what you really want to do, you can keep track of your anonymous functions in a dictionary:

var asteriodsCallbacks:Dictionary = new Dictionary();

Then, you can keep track of the functions there:

asteroidsCallbacks[asteroids[i]] = asteroidsMouseUpHandler;
asteroids[i].addEventListener(MouseEvent.MOUSE_UP, asteroidsMouseUpHandler);

And then when you want to unhook, you can look it up:

asteroids[i].removeEventListener(MouseEvent.MOUSE_UP, asteroidsCallbacks[asteroids[i]]);

Of course, I am ignoring existential checks for simplicity. You’d have to add that as well.