Detecting when a WindowedApplication is activated or deactivated in Adobe AIR

<?xml version="1.0" encoding="utf-8"?>
<!-- http://airexamples.com/2008/12/20/detecting-when-a-windowedapplication-is-activated-or-deactivated-in-adobe-air/ -->
<mx:WindowedApplication name="WindowedApplication_applicationActivate_test"
        xmlns:mx="http://www.adobe.com/2006/mxml"
        layout="vertical"
        verticalAlign="middle"
        backgroundColor="white"
        windowActivate="windowedApplication_windowActivate(event);"
        windowDeactivate="windowedApplication_windowDeactivate(event);">
 
    <mx:Script>
        <![CDATA[
            import mx.controls.Alert;
            import mx.events.AIREvent;
            import mx.managers.PopUpManager;
 
            private var alert:Alert
 
            private function windowedApplication_windowActivate(evt:AIREvent):void {
                lbl.text = evt.type;
                if (alert) {
                    PopUpManager.removePopUp(alert);
                }
            }
 
            private function windowedApplication_windowDeactivate(evt:AIREvent):void {
                lbl.text = evt.type;
                alert = Alert.show("WindowedApplication deactivated");
            }
        ]]>
    </mx:Script>
 
    <mx:Label id="lbl" fontSize="32" />
 
</mx:WindowedApplication>