[flexcoders] popup on screen certer?

[markflex2007]

Hi
 
 I use <s:SkinnablePopUpContainer> build a pop component for mobile app
 
 and use the following code to call the popup
 
 var pop:PopUpWindows =  new PopUpWindows();                             
 pop.open(this,true);
 
 
 but the popup always in top-left location of current page. how to make the 
popup on screen certer 
 
 please help
 
 Thanks for help
 
 Mark