Define RadioButton control with
<?xml version="1.0"?> <mx:Application xmlns:mx="http://www.adobe.com/2006/mxml"> <mx:RadioButton groupName="cardtype" id="americanExpress" label="American Express" width="150" /> <mx:RadioButton groupName="cardtype" id="masterCard" label="MasterCard" width="150" /> <mx:RadioButton groupName="cardtype" id="visa" label="Visa" width="150" /> </mx:Application>