<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml"
        layout="vertical"
        verticalAlign="middle"
        backgroundColor="white"
        initialize="init();" viewSourceURL="srcview/index.html">

    <mx:Script>
        <![CDATA[
            import mx.controls.Alert;

            private function init():void {
                button.addEventListener("labelChanged", button_labelChanged);
            }

            private function button_labelChanged(evt:Event):void {
                Alert.show(evt.toString());
            }
        ]]>
    </mx:Script>

    <mx:ApplicationControlBar dock="true">
        <mx:Button label="One" click="button.label = 'One';" />
        <mx:Button label="Two" click="button.label = 'Two';" />
    </mx:ApplicationControlBar>

    <mx:Button id="button" label="Button" />

</mx:Application>