Error: Access of undefined property in AS3

Question

I'm attempting to learn ActionScript 3 as my first programming language (before this I only did in past some little crap with PHP).

I have this code:

    package 
{
    import flash.display.Bitmap;
    import flash.display.Sprite;
    import flash.events.Event;
    import flash.events.MouseEvent;
    import flash.text.TextField;

    /**
     * ...
     * @author Mattia Del Franco
     */
    [Frame(factoryClass="Preloader")]
    public class Main extends Sprite 
    {
        [Embed(source = "img/pgnew.png")]
        internal var MyImage:Class;
        // La riga embed importa l'immagine, la riga sotto la assegna ad una classe chiamata MyImage

        public function Main():void 
        {
            if (stage) init();
            else addEventListener(Event.ADDED_TO_STAGE, init);
        }

        private function init(e:Event = null):void 
        {
            removeEventListener(Event.ADDED_TO_STAGE, init);
            // entry point

            trace ("Hello World!");
            var myBitmap:Bitmap = new MyImage; //nuova variabile myBitmap al quale viene assegnato la creazione di un nuovo MyImage (trattato come un oggetto)
            addChild( myBitmap );

            var writeText:TextField = new TextField();
            writeText.text = "Ciao Mondo!";
            this.addEventListener(MouseEvent.CLICK, function(){
            addChild(writeText);
            var clicked:Boolean = true;
            return clicked;
            });

            this.addEventListener(MouseEvent.CLICK, function() {
                if (clicked == true) {
                removeChild(writeText);
            } else {
                addChild(writeText);
            }
            });

        }

    }
}

In the second EventListener I'm trying to get the boolean value of clicked (specified in the first EventListener) but when i go to debug this program i get this error:

col: 9 Error: Access of undefined property clicked. if (clicked == true) {

Why this happens?

Answer 1

The reason that you cannot access the "clicked" variable is because this variable is held in a different scope. When you declare a variable within a function (your first Event Listener), it is only accessible from within that function. Your second Event Listener has no access to that variable.

Here is a good way to work around the problem:

       var clicked:Boolean = false;

        var writeText:TextField = new TextField();
        writeText.text = "Ciao Mondo!";
        this.addEventListener(MouseEvent.CLICK, function(){
        addChild(writeText);          
       clicked = true;
        return clicked;
        });

        this.addEventListener(MouseEvent.CLICK, function() {
            if (clicked == true) {
            removeChild(writeText);
        } else {
            addChild(writeText);
        }
        });