addEventListener(Event.COMPLETE, onLoaded) function problem

[lordofthestring]

hi, everyone, i am new and i need help
i hope my problem is not one everyone knows and talks about, but i couldn't really find an answear to it via google, and am a little bit desperate to find a solution..

problem is: the
addEventListener(Event.COMPLETE, onLoaded) does not finish what it should do before i call the
addEventListener(Event.ENTER_FRAME, loop) function, or so it seems..
WHY!?!?

i do not really understand why this is happening, maybe someone can explain to me where my thinking is wrong..

the error msg is:
TypeError: Error #1009: Cannot access a property or method of a null object reference.

that shouldn't be possible tho, since i initialize the concerning variable (sc:Soundchannel) beforehand..

code:

package 
{
    import flash.display.Sprite;
    import flash.events.Event;
    import flash.media.Sound;
    import flash.media.SoundChannel;
    import flash.net.URLLoader;
    import flash.net.URLRequest;

    public class testprojekt extends Sprite
    {
        public var loader:URLLoader = new URLLoader();

        public var sound: Sound = new Sound();
        public var sc:SoundChannel = null;
        public var xml:XML;
        public var il: XMLList = new XMLList();
        
        public var soundIndex:Number = 0;
        public var soundEndIndex:Number;
        
        public var speed:Number = 100;
        
        public var chordList:XMLList;

        public var testString:String;
        
        public function testprojekt()
        {
            loader.load(new URLRequest("sound.xml"));
            
            loader.addEventListener(Event.COMPLETE, onLoaded);

            // chordList from SoundInput class
            var sInput: SoundInput = new SoundInput("soundFile_test.xml");
            chordList = sInput.getSoundInput(); 

            addEventListener(Event.ENTER_FRAME, loop);
        }
        
        public function onLoaded(e:Event):void
        {   
            // xml loaded
            xml = new XML(loader.data);
            il = xml.tracks.sound;
            soundEndIndex = il.name.length();
            
            // start first sound
            sound = new Sound(new URLRequest("sounds/" + il.name[soundIndex]) );            
            sc = sound.play();
            
        }
        
        public function loop(e:Event):void
        {
            //trace("here is the error and i do not know why");
            if (sc.position >= speed) 
            {
                sc.stop();
                setSound();
            }   
        }
        public function setSound():void 
        {
            soundIndex++;
            if (soundIndex < soundEndIndex)
            {
                trace(soundIndex);
                sound = new Sound(new URLRequest("sounds/" + il.name[soundIndex]) );
                trace(il.name[soundIndex]);
                sc = sound.play();
            }
            else
            {
                removeEventListener(Event.ENTER_FRAME, loop);
            }   
        }
    }
}

thx for anyone reading this through

[bloodstyle]

I don't have the faintest clue about sounds, but it looks like you don't initialize the sc variable until the Event.COMPLETE is fired, so that'd be why.

[lordofthestring]

true.. but the Event.COMPLETE should always come and finish the initialisation before the Event.EnterFrame (loop), where sc is needed.. so why is that a problem??

[bloodstyle]

Apparently loading takes longer than the first enter frame event. Why not just add the enter frame listener in the load complete function as well?

[lordofthestring]

omg.. of course.. lol.. works..

don't really get it tho.. why does it not wait until it is loaded before moving on with the code..?

strange behaviour..

[lordofthestring]

great, i think i have the same problem again, but this time i cannot solve it like before..

new class with constructor:

private var chordList: XMLList = null;

public function SoundInput(sInput:String)
        {
            soundFileInput = sInput;    
            loader.load(new URLRequest(soundFileInput));
            
            loader.addEventListener(Event.COMPLETE, onLoaded);
        }

private function onLoaded(e:Event):void
        {   
            // xml loaded
            xml = new XML(loader.data);
            chordList = xml.trackName.chords.ch;
            
            trace("SoundInput in constructor: " + chordList);         
        }

and getter

ublic function get getSoundInput():XMLList
        {
            return chordList;
        }

but the chordList variable in the getter method does not have a value (null, as initialized above), because at the time i call the getter, the event.complete doesn not seem to be finished..

[QuantumTiger]

Originally Posted by lordofthestring

don't really get it tho.. why does it not wait until it is loaded before moving on with the code..?

strange behaviour..

Events allow you to place behaviour asynchronously (ie it is exactly so that it does not wait before moving on) which means that you can request a loader and do other things in the meantime (such as display a splash screen, a loading progress bar etc). It does, however, take a bit of getting used to if you're new to it particularly because sometimes you have no option but to wait for things to complete.

In terms of waiting there are numerous options for how to achieve that, for example passing a function to your onLoaded event which it calls once it is ready to continue, using a timer to poll your getter (ie if it returns null you wait a short period and try again) or dispatching a custom event from your onLoaded function and setting up an event listener for that which then calls the getter and contines with your code.

[lordofthestring]

hi, thanks for explaining that behaviour.. didn't really make sense to me so far..

unfortunately i still am struggling creating a timer or custom event to wait for it to finish loading..

could you tell me how to access the getter from another class, making sure the value is not null??

i tried it something like that,

while (this.chordList == null)
            {
                this.timer.addEventListener(TimerEvent.TIMER, sInput.getSoundInput);
                this.timer.start();
            }

but it doesn't work that way of course..

from the getter i tried:

public function get getSoundInput():XMLList
        {
            while (chordList == null)
            {
                this.timer.addEventListener(TimerEvent.TIMER, onComplete);
                this.timer.start();
            }
            return this.chordList;
        }

but i guess i am on the wrong track again...

[Dail]

cant you just test if the value is null and return something if it is?

return value!=null ?returnValue:returnOtherValue

[QuantumTiger]

You could try something like

private var t:Timer
private var chordList: XMLList = null;

public function CheckXMLReady():void
{
  t = new Timer(500, 0);
  t.addEventListener("timer", GetSoundInput);
  t.start();
}
        
private function GetSoundInput(e:Event):void
{
  chordList = sInput.getSoundInput(); 
  if (chordList != null)
  {
    // Kill the timer and remove the listener
    t.removeEventListener("timer", GetSoundInput);
    t.stop();
    // call your continuation code here
  }
}

Probably a bit of a kludge - you may be better using custom events (see http://curiousmindsmedia.wordpress.c...vent-tutorial/ for a tutorial)