问mxml空引用

EN

<?xml version="1.0" encoding="utf-8"?>
<mx:VBox xmlns:mx="http://www.adobe.com/2006/mxml">
    <mx:RadioButton id="radio" />
    <mx:Script>
        public override function set label(value:String):void { 
            this.radio.label = value;
        }
        public override function get label():String {
            return this.radio.label;
        }
    </mx:Script>
</mx:VBox>

<?xml version="1.0" encoding="utf-8"?>
<mx:WindowedApplication xmlns:mx="http://www.adobe.com/2006/mxml"  xmlns:local="*">
    <local:CustomRadio  label="xxx" />
</mx:WindowedApplication>