如何确定哪个视图控制器当前处于活动状态/显示视图的视图控制器？

Question

In my app I am queueing some local notifications, when they fire I must present a modal view. The trouble is I have numerous view controllers any one of which could currently be active and thus the one that needs to present the modal view controller. How can I determine which one is currently in use?

I am setting a navigation controller as the windows root view controller, and this can push any number of other view controllers, some of them themselves may also be currently presenting another view controller modally. This must work on iOS 4 and 5.

I have a lot of view controllers so would like to avoid putting code in each of them to each check if they are currently the top one.

Answer 1

You can look at the navigation controller's topViewController property to find out which controller is at the top of the stack. This will be the one whose view is displayed.

Since you may also be presenting a modal view controller, you'll probably be more interested in the visibleViewController property, which will give you the controller for the current view whether its presented modally or pushed onto the navigation stack.

Answer 2

Create a variable that stores a pointer to the ViewController that was most recently pushed. Every time you push a new ViewController, update this variable. Then you'll always know which one is on the top!