MovieClip isn't removed from Dictionary

Question

I have a Dictionary where I hold data for movieclips, and I want the data to be garbage collected if I stop using the movieclips. I'm using the weak keys parameters, and it works perfectly with other data, however I've run into a problem.

This code works great:

var mc = new MovieClip();
var dic = new Dictionary(true);
dic[mc] = 12;
mc = null;
System.gc();
System.gc();
for (var obj in dic)
   trace(obj);    //this doesn't execute

But when I actually use the movieclip, it stops working:

var mc = new MovieClip();
var dic = new Dictionary(true);
dic[mc] = 12;
addChild(mc);
removeChild(mc);
mc = null;
System.gc();
System.gc();
for (var obj in dic)
   trace(obj);    //this prints [object Movieclip]

Why does this happen? Is it something I'm doing wrong? Is there a workaround?

Edit: I know that for this specific example I can use delete dic[mc], but of course this is a simplified case. In general, I don't want to manually have to remove the movieclip from the dictionary, but it should be automatic when I don't reference it anymore in the rest of the application.

Edit2: I tried testing what Aaron said, and came up with just weird stuff... just iterating the dictionary (without doing anything) changes the behaviour:

var mc = new MovieClip();
var dic = new Dictionary(true);
dic[mc] = 12;
addChild(mc);
removeChild(mc);
mc = null;

for (var objeto in dic) {}    // <-- try commenting out this line

addEventListener('enterFrame', f);  // I print the contents every frame, to see if
                                    // it gets removed after awhile

function f(evento)
{
    System.gc();
    System.gc();

    for (var objeto in dic)
        trace(objeto);
}

This keeps printing [object Movieclip] every frame, unless I comment out the indicated line, where it doesn't print anything.

Answer 1

I believe that the problem is one of timing. I think that when you call remove child, the reference count isn't getting updated until later in the "frame". (I think this is what is happening anyway.)

The code below demonstrates why I think this is true. (I'm using flex, but it appears to reproduce your issue.)

The code below outputs:

[object MovieClip]
here

If you call otherfoo directly at the end of somefoo(), you get:

[object MovieClip]
here
[object MovieClip]

---

<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml" layout="absolute" mouseDown="somefoo()">
<mx:Script>
 <![CDATA[
  import mx.core.UIComponent;
  private var dic:Dictionary = new Dictionary(true);
  private var ui:UIComponent = new UIComponent();
  private var mc:MovieClip = new MovieClip();

  private function somefoo():void {
   this.addChild(ui);

   dic[mc] = 12;
   ui.addChild(mc);
   ui.removeChild(mc);
   for (var obj:Object in dic)
      trace(obj);    //this prints [MovieClip]

   this.removeChild(ui);

                            // callLater causes the function to be called in the _next_ frame.
   callLater(otherfoo);
  }

  private function otherfoo():void
  {
   trace("here");
   mc = null;
   System.gc();
   System.gc();

   for (var obj:Object in dic)
      trace(obj);    //this prints [MovieClip]

  }
 ]]>
</mx:Script>
</mx:Application>

Answer 2

In you're example code here you're never adding the movieclip to the dictionary, but the int 12 instead? Probably a typo.

If you want the dictionary to have a list of what's currently on the stage, why not have i as a util class instead that listens to Event.ADDED_TO_STAGE and Event.REMOVED_FROM_STAGE and modify the dictionary accordingly? A dictionary doesn't automatically delete references if they get removed from the stage. Also gc in this case has nothing to do with this.