Resize effect maintaining the window centered

Question

I have a TitleWindow that I open using the PopUpManager.
PopUpManager.centerPopUp(paymentWindow);       
I would like to apply a resize effect when I show the window.
<mx:Resize id="expand"  widthTo="640" heightTo="480"/>
The problem is that the TitleWindow is resized from the upper left corner to the bottom right corner. So the popup is no more centered. How can I apply the same effect but maintaining the window centered in the screen while it is resized?

Answer 1

I don't understand completely.But below is a piece of code I wrote render a image as a zoom popup and then when i cliked on the pop up it resized to its original size. May be it can help you
use :-
img.addEventListener(MouseEvent.CLICK, image_click);
img.addEventListener(ResizeEvent.RESIZE, image_resize);
PopUpManager.addPopUp(img, this, true);
and
private function image_click(evt:MouseEvent):void {
                    PopUpManager.removePopUp(evt.currentTarget as Image);
private function image_resize(evt:ResizeEvent):void {
                   PopUpManager.centerPopUp(evt.currentTarget as Image);
If you are using image.