UINavigationController

I have a few items on my navigation stack, when I press the Home button and then re-enter the application, how do I know what item/navigation item is开发者_开发知识库 currently shown?

I've tried using the NSNotificationCenter but its not working as I'd like. If I register an observer on the controller, each time the application becomes active this is fired but I would like it to fire only if its on the current item on the stack.

I've also tried using the windows.subview but when you compare the type of UIView against the subview it doesnt always work. i.e. if([windows.subviews objectAtIndex:0] == controllername.view)