Open Radar

 
Summary: 

Requesting a standard mechanism to capture when a user has tapped the 'back' button in a UINavigationController. Currently, the only way to do this is by overriding the viewWillDisappear method on the current view controller. However, that method is called when we're navigating forward, backward, or if a modal dialog is brought up over the current controller. 

Notification of the back button is needed in cases where the view controller has to perform some sort of clean-up work. 

It should be pointed out that there is currently support for {will|did}ShowViewController methods under UINavigationControllerDelegate but these are invoked only when a view is appearing. A corresponding {will|did}HideViewController methods with a flag indicating backward vs. forward would solve the problem.

Steps to Reproduce:

- Create a UINavigationController.
- Push a couple of view controllers onto the stack.
- Try to capture when the user has pressed the 'Back' button.
- In the second view controller, override viewWillDisappear, then observe that it gets called when going to third controller or when going back. If a modal dialog is popped in front, viewWillDisappear will also get called.