Jun 24, 2005 - Capturing Tab Change Event and Cancelling
Using a TabNavigator, how to force workflow

From Mika Kiljunen

 You'll have to extend the TabNavigator and override the selectedIndex setter.

<!-- MyTabNavigator.mxml -->
<?xml version="1.0"?>
<mx:TabNavigator xmlns:mx="http://www.macromedia.com/2003/mxml"
  xmlns="*">
  <mx:Script>
    var savedSelectedIndex:Number;
    public function set selectedIndex(value:Number):Void
    {
      savedSelectedIndex = value;
      tabBar.selectedIndex = super.selectedIndex;
      confirm("Are you really, really sure?");
    }
  </mx:Script>
</mx:TabNavigator>

In your alert handler you set the selectedIndex to the
savedSelectedIndex (if the user clicked OK).