preloading external .swf with class file as3 - actionscript-3

Question

so i'm trying to make an external preloader to load my main .swf (loading.swf) 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.

Answer 1

(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.

Answer 2

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)?

Answer 3

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.

Answer 4

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.