I can't obtain the stage's sizes

Question

Situation:
I've got 2 swf files, 1 is a preloader which loads the 2nd swf file, my site.
Both of them, if started separately, work correctly.
Problem:
when I put the files together, linking the site's swf to the preloader, I get a  null element error and the site loads not correctly.
What I've understood:
The preloader is ok, because I can remove the error message working on the site's swf AS code.
In the preloader's code I have some lines to center its animation on the stage, I do that like this:
import flash.display.Stage;
var myStage:Stage = this.stage;
then using myStage.stageWidth and myStage.stageHeight I calculate the clip position
Also on the site's code I do the same to center a movieclip using exactly the same code, but it doesn't work and I've found that the problem is the myStage variable, not because it has the same name as the variable on the other file (I've tried to name it myFrame).
It looks that on the site's swf the myStage variable can't be assigned and then results to be null.
Question:
How can I obtain the stage's height and width since
var myStage:Stage = this.stage;
doesn't work?

Answer 1

Hi Kumidan,
As far I have understood, you want to know the stage dimensions in order to center movie clips.
Whether on your preloader or your site SWF.
I am a beginner in AS3 but the way you create a new instance of the stage is weird.
Your movie can only have one stage.
Why dont you add a listener to the stage.
Here is something in AS3  :
stage.addEventListener(Event.RESIZE, resizeHandler);    // adding the listenener
resizeHandler (null);    // initializing value
function resizeHandler (event:Event):void
var sw:Number = stage.stageWidth;
var sh:Number = stage.stageHeight;
blahblahblah   // code that place your clips according to the stage dimensions sh and sw