Creating custom event handlers in ActionScript 3 is pretty much simple. Here is a simple example which loads an image and fires a custom event named “onImageLoad” as soon as image is loaded.

Class imageLoader.as

package {
import flash.events.*;
import flash.net.URLRequest;
import flash.display.Loader;
import flash.display.Sprite;
public class imageLoader extends EventDispatcher {
private var _mc:Sprite;
private var url:String;
private var loader:Loader;
public function imageLoader(_mc:Sprite, url:String) {
this._mc = _mc;
this.url = url;
loadImg();
_mc.addChild(loader);
}
private function loadImg():void {
loader = new Loader();
loader.contentLoaderInfo.addEventListener(Event.COMPLETE, onComplete);
loader.contentLoaderInfo.addEventListener(IOErrorEvent.IO_ERROR, onIOError);
var request:URLRequest = new URLRequest(url);
loader.load(request);
}
private function onComplete(event:Event):void {
dispatchEvent(new Event("onImageLoad"));
}
private function onIOError(event:IOErrorEvent):void {
trace("IO Error.");
}
}
}

Now in Flash, create a a object of imageLoader class and add a event listener (for our custom event “onImageLoad”).

var myImageLoader:imageLoader = new imageLoader(this, "images/someImg.jpg");
myImageLoader.addEventListener("onImageLoad", callbackHandler);
function callbackHandler(event:Event) {
trace("Image Loading Complete!");
}

Now test the file. Be sure to have someImg.jpg in images folder. Once image is loaded, you should be able to see ”"Image Loading Complete!” message in output window.