How to hide the closeButton in ContentNavigator ?

[TristoneZhang]

I'm using ArcGIS for flex 3.6 API. And I wanna set the closeButton invisable in my contentNavigator.
But when I try to get the closeButton object, it returns null. As you can see the picture below.
Looking forward to your help.
[ATTACH=CONFIG]30553[/ATTACH]


well??fixed by myself :
contentNavigator.addEventListener(FlexEvent.CREATION_COMPLETE,function(event:FlexEvent):void{
     contentNavigator.closeButton.visible = false;
    })