Question

If I have added Event.ENTER_FRAME listeners to different components, how can I set or know the ordering of when these events will be fired on each enterFrame?

Instead of adding enterFrame listeners to individual elements, is it better practice to have one element which listens for enterFrame events, and has an array of elements needing updating on enterFrames, thereby making it easy to organize and change the firing order of these events?

Answer 1

You can prioritize event listeners, thereby ordering the execution of them. Use the fourth property of addEventListener(), an integer that indicates priority. Event listeners added with a high priority integers will be executed before those with lower priority. See the addEventListener() reference for more information.

But you are also right that it is usually a better idea to create your own update manager. This is because event listeners require an Event (or sub-class thereof) to be instantiated, which can greatly affect performance (instantiation is one of the most heavy tasks in the Flash runtime.) This is especially unfortunate with ENTER_FRAME events, as you will often not use the event object anyway.

Create a manager class, from which other parts of your application may subscribe to update callbacks. Whenever a callback is registered, add one ENTER_FRAME (or TimerEvent.TIMER) event listener inside the manager class that invokes all callbacks. When the last callback is removed, remove the event listener as well.

While on the topic of events and performance, you might be interested to know that for events that bubble (most interaction events that take place in the display list), a new event object is created for each dispatcher that the event passes during the bubbling! It’s always a good idea to remove event listeners whenever you don’t need them.