flex内存泄露解决之道

（1）Event Listeners
                Listening to parent objects does cause memory leaks
                e.g.
                    override protected function mouseDownHandler(…):void {
                     systemManager.addEventListener(“mouseUp”, mouseUpHandler);
              you can:
                1.Removing the addEventListener (when dispose).
                  systemManager.removeEventListener(“mouseUp”, mouseUpHandler);
                2. Use of weak reference listeners
                  override protected function mouseDownHandler(…):void {
                  systemManager.addEventListener(“mouseUp”, mouseUpHandler, false, 0, true);
              These do not block garbage collection(generally do not cause memory leaks):
Weak References
Self References
References to Child Objects
                    weak reference event listener  e.g.
                &nb