[flexcoders] verticalscrollbar not showing after addChild

[netdeep]

My application accepts input and adds charts to itself via addChild in 
actionscript.  However, no matter how many charts I add, the app never shows a 
vertical scrollbar until the user manually resizes the browser window.  How do 
I fix this quirk?

I found this snippet on the web, but it doesn't work.  In fact, when the Alert 
box pops up, measuredHeight is always less than height so the problem seems to 
be that flex is not calculating the height correctly.  I tried 
invalidateDisplayList() but that didn't work either.

override public function validateSize(recursive:Boolean = false):void {
                                super.validateSize(recursive);
                                if (!initialized) return;
                                Alert.show("ht: "+height,"measured ht: 
"+measuredHeight);
                                if (height < measuredHeight) 
verticalScrollPolicy = ScrollPolicy.ON;
                                else verticalScrollPolicy = ScrollPolicy.OFF;
                        }