Dispatching a simple event from classB to ClassA

Question

Hi,
I have read at multiple places tutorials/explanations on the EventDispatcher use in AS3 and that confuses me a lot. I would appreciate a lot if somebody could show me in the simple exemple below how I should do to just send a simple message from a ClassB to a Class A. In the exemple below that I made, I have classA that calls classB to send a message that ClassA then gets. Of course, I simplified to the minimum the 2 classes to allow focusing on the problem. Currently, the exemple does NOT work, i.e. the line "trace ("message was received!");" is not executed.
I saw in several exemples on the web that some put the addEventListener on the EventDispatcher object. I do not understand the logic behind this, I would put the addEventListener on the objects that will receive the message.
I wonder also why can't I just put an addEventlistener at the ClassA constructor "addEventListener("hello", receivedHello);" and then send a dispatchEvent from classB. I tried that as well but it does not work.
package {
    import flash.display.MovieClip;
    import flash.events.Event;
    public dynamic class ClassA extends MovieClip{
        public function ClassA(){
            ClassB.getClassB().registerUser(this);
            ClassB.getClassB().sendMessage();
        public function receivedHello(e:Event){
            trace ("message was received!");
package{
    import flash.events.Event;
    import flash.events.EventDispatcher;
    class ClassB {
        public var sender:EventDispatcher;
        // constructor
        public function ClassB() {
            sender= new EventDispatcher();
        // function getClassB() to be sure only one instance of this class is running
        public static function getClassB():ClassB {
            if (ClassB._instance == null) {
                ClassB._instance = new ClassB();
            return ClassB._instance;
        public function registerUser(user:Object){
            user.addEventListener("hello", user.receivedHello);
        public function sendMessage(): void {
            sender.dispatchEvent(new Event("hello"));
Thanks so much in advance for your help
Pieter

Answer 1

package {
    import flash.display.MovieClip;
    public dynamic class ClassA extends MovieClip{
        public function ClassA(){
           addEventListener("customEvent",f);
        function f(e:Event){
            trace("event received");
package{
   import ClassA;
    import flash.events.Event;
    import flash.events.EventDispatcher;
    class ClassB {
        // constructor
        public function ClassB() {
             var a:ClassA = new ClassA();
             a.dispatchEvent(new Event("customEvent"))