preloading external .swf with class file as3

so i'm trying to make an external preloader to load my main .swf (loading.sw开发者_JAVA百科f) file that has a class file named mainLoading.as using this code:

var l:Loader = new Loader();
l.contentLoaderInfo.addEventListener(ProgressEvent.PROGRESS, loop);
l.contentLoaderInfo.addEventListener(Event.COMPLETE, done);
l.load(new URLRequest("loading.swf"));
var loadingPage:loading = new loading;

function loop (e:ProgressEvent):void{
    addChild(loadingPage);
    loadingPage.x = stage.stageWidth/2;
    loadingPage.y = stage.stageHeight/2;

}

function done (e:Event):void{
    removeChild(loadingPage);
    addChild(l);
}

so I'm getting an error message saying:

TypeError: Error #1009: Cannot access a property or method of a null object reference. at mainLoading()

I think i'm getting the error message because i am accessing the stage in my mainLoading() class file. I tried adding this to the constructor in my class file but it didn't work:

public function mainLoading () {
    addEventListener(Event.ADDED_TO_STAGE, init);   
}
private function init(e:Event): void {
    initStartUpScene ();

}

my initStartUpScene function just throws the intro scene to the loading.swf

any suggestions?

thanks for your help.

---

(question) is your mainLoading extends either Sprite or Movieclip ?

EDIT

After reading your comment, I would suggest trying this :

Add a function call inside the swf content in your complete progress handler :

function done (e:Event):void{
    removeChild(loadingPage);
    addChild(l);
    Object(l.content).initMethod();
}

content let you access the methods in your loaded .swf main class (e.g. mainLoading)

And replace the event handling in your mainLoading by :

public function mainLoading () {
    //no event handling in constructor
}

public function initMethod():void {
    //here you go
    init();
}

public function init():void { ... //No more event here

Btw it's not the cleanest way to solve your problem.

---

If that's the exact message you are getting, then yes, adding the ADDED_TO_STAGE listener should have fixed it. Remember to recompile the "loading.swf" if you make any changes to it (a step I always seem to forget)

Does "loading.swf" run just fine without any errors when running it on it's own (not loading it into the "container" SWF)?

---

This may be unrelated to the question you asked, but you might get better results and avoid some errors by structuring your code like this:

var loadingPage:loading = new loading;
addChild(loadingPage);
loadingPage.x = stage.stageWidth/2;
loadingPage.y = stage.stageHeight/2;

var l:Loader = new Loader();
l.contentLoaderInfo.addEventListener(ProgressEvent.PROGRESS, onProgress);
l.contentLoaderInfo.addEventListener(Event.COMPLETE, onComplete);
l.load(new URLRequest("loading.swf"));

//I renamed this function since I believe "loop" is a reserved keyword.
function onProgress (e:ProgressEvent):void{
    //No code needed
}

function onComplete (e:Event):void{
    removeChild(loadingPage);
    addChild(l);
}

You can remove the "onProgress" function if you won't be needing it as well.

---

OOOOOOKKKKK, so after about a week of admitting defeat, trying it again, rewriting almost half of my code, trying to convince myself that preloaders are overrated, i finally figured it out (drum roll please):

I had a variable that was referencing the stage being called before my constructor method was called. like this:

private var xScrollPosRight:Number = stage.stageWidth - xScrollPosLeft;

I just changed stage.stageWidth to 750 and it worked.

live and learn.