root and stage

var rec1:Shape = new Shape();

var rec2:Shape = new Shape();

var rec3:Shape = new Shape();

var spriteOnDisplayList:Sprite = new Sprite();

var spriteNotOnDisplayList:Sprite = new Sprite();

var spriteOnMainClass:Sprite = new Sprite();

spriteOnDisplayList.addChild(rec1);

spriteNotOnDisplayList.addChild(rec2);

spriteOnMainClass.addChild(rec3);

stage.addChild(spriteOnDisplayList);

//stage.addChild(spriteNotOnDisplayList);

this.addChild(spriteOnMainClass);

trace(rec1.root); //[object Stage]

trace(rec2.root); //null

trace(rec3.root); //[object MainTimeline]

一個display物件在它的constructor中, 其parent, root, stage等instance variable都是null值.

因為它尚未加入display list.