Is it possible to listen the event triggered by another class?

Question

I've got 3 classes:

The class that recognizes the change in URL (using SWFAddress by Asual):

package swfaddress {

import flash.display.MovieClip;
import com.asual.swfaddress.*;

 public class SwfAddress extends MovieClip {

 private var dispatcher:Dispatch = new Dispatch;

 public function SwfAddress():void {
  SWFAddress.addEventListener(SWFAddressEvent.CHANGE, onChange);
 }

 private function onChange(e:SWFAddressEvent):void {
  dispatcher.changed();
 }
}
}

The class "Dispatch" that validates the URL and dispatching Event when finished

package swfaddress {
 import flash.events.Event;
 import flash.events.EventDispatcher;

 public class Dispatch extends EventDispatcher {

  public static const CHANGED:String  = "changed";

  public function changed ():void {

    // some operations validating the URL

   dispatchEvent(new Event(Dispatch.CHANGED));
  }
 }
}

Other class in other package that should receive info when the validation process has finished.

package menu {
import swfaddress.*

public class MenuPanel extends MovieClip {
var swfRead:Dispatch = new Dispatch;

public function MenuPanel():void {
 swfRead.addEventListener(Dispatch.CHANGED, onChange);
}

private function onChange(e:Event):void {
 trace("Hello World");
}
}

And the "Hello World" never appeared in the output window - so I'm not sure if it's possible that my MenuPanel has a chance to receive an info about completing the validation triggered by some other class?

Answer 1

You are creating two different instances of the dispatcher, and so the instance that is being called to validate your URL is not the same instance that you are listening to in the MenuPanel class.

A simple way around this would be to make the Dispatch class a singleton, so that only one instance of it exists and you can reference it from different points in your application. This works by giving the Dispatch class a static method that returns a self-contained instance of itself. You then call Dispatch.getInstance() whenever you want a reference to the class instead of using the new keyword.

Dispatch:

package swfaddress
{
    import flash.events.Event;
    import flash.events.EventDispatcher;


    public class Dispatch extends EventDispatcher
    {
        // singleton instance
        private static var _instance:Dispatch;
        private static var _allowInstance:Boolean;

        public static const CHANGED:String  = "changed";

        // get singleton instance of Dispatch
        public static function getInstance():Dispatch 
        {
            if (Dispatch._instance == null) {
                Dispatch._allowInstance = true;
                Dispatch._instance = new Dispatch();
                Dispatch._allowInstance = false;
            }
            return Dispatch._instance;
        }

        public function Dispatch() 
        {
            if (!Dispatch._allowInstance)
            {
                throw new Error("Error: Use Dispatch.getInstance() instead of the new keyword.");
            }
        }

        public function changed():void {
            //some operations validating the URL
            dispatchEvent(new Event(Dispatch.CHANGED));
        }
    }
}

Getting a reference:

private var dispatcher:Dispatch = Dispatch.getInstance();