[flexcoders] Generic showPopupWindow function

[markgoldin_2000]

I am trying to create a generic showpoppup function:
public function showPopupWindow(parent:DisplayObject, 
WhatToShow:String):void
{
var helpWindow:TitleWindow =
TitleWindow(PopUpManager.createPopUp(parent, WhatToShow, true));
PopUpManager.centerPopUp(helpWindow);
}       

But WhatToShow is a string and not taken by PopUpManager.createPopUp.
How can I specify a class to show?

Thanks