When do display objects get a size?

Question

I am testing parts of an application as actionscript-only and then merge them into a flash project.
Now, when testing, this works fine
var s1:Sprite = new Something1();
addChild(s1);
var s2:Sprite = new Something2();
s2.y = s.y + s1.height;
addChild(s2);
things align perfectly. When I do the same in flash, s1.height is 0 and objects sit on top of each other ....?

Answer 1

some components or children of components are not rendered as soon as they're instantiated.
in that situation, you can use the render event or one enterframe loop or a time delay (of less than 100ms) to access display properites like width and height of your object:
var whatever:Whatever=new Whatever();
whatever.addEventListner(Event.RENDER,f);
stage.invalidate();
function f(e:Event):void{
trace(whatever.width,whatever,height);
if you have a custom class, the object may not be drawn in your class until much later than the next stage render event.  in that situation, you should dispatch an event from your class and use a listener for that event.