Mega Code Archive
A basic validator for requirement
<![CDATA[
<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml">
<mx:Validator source="{username}" property="text" required="true" />
<mx:Text text="Enter your username:" />
<mx:TextInput id="username" />
</mx:Application>
]]>