Can't get stage from a constructor method. Why?

Hi,

I'm making a kind of image showcase, what has a fluid width and height, depending on browser window dimensions. Everything is okay, I have other kind of issue: in constructor function in this gallery class I can't use stage property, I have to get it from main class.

Why Flash treats me this way and how I can avoid this currentStage variable?

Main code:

package dev {

     import flash.display.Sprite;

     import flash.display.StageScaleMode;

     import flash.display.StageAlign;

     import flash.display.MovieClip;

     import flash.events.Event;

     import UI.BackgroundImageRotator;

     public class Application extends Sprite {

          public function Application():void {

               stage.scaleMode = StageScaleMode.NO_SCALE;

               stage.align = StageAlign.TOP_LEFT;

               trace("Start.");

               var BIR = new BackgroundImageRotator(stage);

               stage.addChild(BIR);

          }

     }

}

BackgroundImageRotator class:

package UI {

     import flash.display.MovieClip;

     import flash.events.Event;

     import flash.display.Stage;

     public class BackgroundImageRotator extends MovieClip {

          protected var currentStage:Stage;

          public function BackgroundImageRotator(currentStage:Stage):void {

               this.x = 0;

               this.y = 0;

               this.currentStage = currentStage;

               currentStage.addEventListener(Event.RESIZE, onStageResize);

          }

          protected function onStageResize(evt:Event):void {

               trace(stage.stageWidth + ' ' + stage.stageHeight);

          }

     }

}