AS3 Snippet #2: Watch for changing properties

Today I stumbled across a handy utility class called ChangeWatcher, which lives inside the mx.binding.utils package. It provides you with a handy way of watching other object’s properties.

Here’s how it’s used:

ChangeWatcher.watch(object, “property”, handler);

Object – the object which owns the property
“property” – the property you want to watch
handler – the function name of the handler

Whenever the property of the object changes, the handler will respond. Quite handy, right?

edit:

Here’s an example for you:

Let’s say we have a class called WatchMe. Inside that class we have a public variable called ImBeingWatched. We’d like to trigger a function whenever this variable changes. To do this, we simply add one line of code:

package
{
	import mx.binding.utils.*;
	import flash.display.*;
	import flash.events.*;
 
	public class WatchMe extends MovieClip
	{
		[Bindable] public var ImBeingWatched:Boolean = true;
 
		public function WatchMe():void
		{
			ChangeWatcher.watch(this, "ImBeingWatched", doSomething);
		}
 
		private function doSomething(e:Event):void
		{
			// do something ...
		}
	}
}

As you can see, this works pretty much like using [Bindable] variables. But, in some cases this method proves quite handy.

Update: Oops! Typo. The property that ChangeWatcher is watching must be [Bindable] and Public for it to work.