flex 监听浏览器关闭或刷新

mxml内嵌代码：

应用加载完成注册一下：creationComplete="reg()"

public function reg():void{    
            if(flash.external.ExternalInterface.available){
                var jsStr:String; 
                jsStr = 
                    'eval(\'window.onbeforeunload = onbeforeunloadHandler;' +
                        'function onbeforeunloadHandler(){' +
                            'var swfRef = document.'+FlexGlobals.topLevelApplication.className+' || window.'+FlexGlobals.topLevelApplication.className+';'+
                            'swfRef.windowCloseHandler();' +
                            'return "退出系统提示";' +
                        '}\')';
                flash.external.ExternalInterface.call(jsStr);
                flash.external.ExternalInterface.addCallback('windowCloseHandler',externalWindowCloseHandler);
            }
        }
            
            public function externalWindowCloseHandler():void{
            //    Alert.show("aaaaa");
            }