<?xml version="1.0" encoding="utf-8"?>
<!-- http://blog.flexexamples.com/2008/06/25/detecting-when-the-label-changes-on-a-button-control-in-flex/ -->
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml"
        layout="vertical"
        verticalAlign="middle"
        backgroundColor="white"
        initialize="init();">

    <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>


<?xml version="1.0" encoding="utf-8"?>
<!-- http://blog.flexexamples.com/2008/06/25/detecting-when-the-label-changes-on-a-button-control-in-flex/ -->
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml"
        layout="vertical"
        verticalAlign="middle"
        backgroundColor="white"
        initialize="init();">

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

            private var button:Button;

            private function init():void {
                var btnOne:Button = new Button();
                btnOne.label = "One";
                btnOne.addEventListener(MouseEvent.CLICK, setBtnLabel);

                var btnTwo:Button = new Button();
                btnTwo.label = "Two";
                btnTwo.addEventListener(MouseEvent.CLICK, setBtnLabel);

                var appControlBar:ApplicationControlBar = new ApplicationControlBar();
                appControlBar.dock = true;
                appControlBar.addChild(btnOne);
                appControlBar.addChild(btnTwo);
                Application.application.addChildAt(appControlBar, 0);

                button = new Button();
                button.label = "Button";
                button.addEventListener("labelChanged", button_labelChanged);
                addChild(button);
            }

            private function setBtnLabel(evt:MouseEvent):void {
                button.label = Button(evt.currentTarget).label;
            }

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

</mx:Application>