Monitor collection change

[mark goldin]

I have an ArrayCollection. I need to monitor changes made to it by a user.
I am trying something like this:
aWatcher = ChangeWatcher.watch(_model.selectedPoints, "Selected",
validateSaveState);

private function validateSaveState(event:CollectionEvent):void
{
trace(event);
}

But I am not really getting into validateSaveState when selected property
is changed.

Please give me some ideas.

Thanks