Open Radar

 
Summary:
First of all, the navigation controller delegate is set to a delegate that provides the necessary components for custom view controller animations for pushing and popping, that are interactive and interruptible. 

When finishing a current view controller animation transition that was previously canceled in the same context, the navigation bar items are incorrect.

Steps to Reproduce: 
1. Open the PullToPopDemo project and build and run.
2. Notice the initial state of the navigation bar with just the PullToPop title.
3. Swipe upward, without interrupting the transition.
4. Notice the navigation bar  now includes bar button items for Back, Edit, and New buttons.
5. Swipe downward, without interrupting the transition.
6. Notice that the navigation bar is back to the same initial state as step 2.
7. Now swipe upward, just enough to start the transition animation, but NOT far enough for it to pass the threshold to finish the transition.
8. BEFORE the animation returns to its start position, interrupt it, and swipe fully upward so as to complete the transition.
9. Notice the navigation bar is lacking the navigation item of the destination view controller. In particular, the Back, Edit, and New bar button items are missing.

This seems to only happen when within a particular transition context, when cancelInteractiveTransition() is called, followed eventually by finishInteractiveTransition()

Expected Results:
The navigation bar displays the navigation items associated with the destination view controller of an animated, interruptible, view controller animation transition.

Actual Results:
The navigation bar in its finished state is missing the navigation item associated with the destination view controller.

Version/Build:
11.2.6 (15D100)

Configuration:
iPhone X, iPhone 7 tested