Anna Filina

g-speak overview 1828121108 from john underkoffler on Vimeo.

An object that has no references to it will be eventually garbage-collected. An event listener is also a reference, thus preventing it from being removed from memory.

In order to allow your objects to be garbage-collected, you can either remove all listeners from it or use weak event listeners instead (don’t forget to remove other references to it as well). To make a listener weak, you must set the 5th parameter of the addEventListener method to true, like this:

var btn:Button = new Button();
btn.addEventListener(MouseEvent.CLICK, clickHandler, false, 0, true);

But you have to be very careful where you use weak event listeners. When you instantiate an object in a function’s scope and then add weak event listeners, your object could be garbage-collected before it had a chance to dispatch these events. Example:

private function getStuff():void {
    var service:HTTPService = new HTTPService();
    service.url = "get-stuff.php";
    service.addEventListener(ResultEvent.RESULT, resultHandler, false, 0, true);
}

In this case, you should either avoid using weak listeners and remove them manually, or add a reference to your object outside of the function’s scope to prevent it from being garbage-collected too early.

I recorded part of the Flex and Zend presentation by Kevin Hoyt (took me some time to transfer, encode and upload).

ZIP with the source code
Kevin Hoyt’s blog post on this topic