[flexcoders] Spark layout / horizonal and vertical centered button

[Markus]

Hello, 

this might be an easy question but at the moment I am not sure how to do this. 
I want to use the new Spark layout and display a button that is horizontal and 
vertical centered in the middle. 

I have tried the following code but it didn't work.

<?xml version="1.0" encoding="utf-8"?>
<s:Application xmlns:fx="http://ns.adobe.com/mxml/2009"; 
    xmlns:s="library://ns.adobe.com/flex/spark" 
    xmlns:mx="library://ns.adobe.com/flex/halo" minWidth="1024" minHeight="768">
        
    <s:Group width="100%" height="100%">                
       <s:HGroup verticalAlign="middle" width="100%" height="100%">             
        
           <s:VGroup width="100%" height="100%" horizontalAlign="center">
              <s:Button label="button1"/>
            </s:VGroup>
        </s:HGroup>
     </s:Group>
</s:Application>

Any suggestions or examples?

Regards Markus

BTW: Does anybody know where to get the source code from Glenn Ruehle's 
presentation about Spark layouts on the MAX 2009?