UINavigationController custom animation prevents swipe-to-go-back from working

Question

I noticed something strange and may possibly be a bug in UINavigationController. When you override -navigationController:animationControllerForOperation:fromViewController

Answer 1

If you've subclassed UINavigationController, the simplest fix is as follows (iOS 9.3, Swift 2.2):

override func viewDidLoad() {
    super.viewDidLoad()
    interactivePopGestureRecognizer?.delegate = nil
}

Alternatively, in any other instance of UIViewController:

override func viewDidLoad() {
    super.viewDidLoad()
    navigationController?.interactivePopGestureRecognizer?.delegate = nil
}

Implementing the delegate method navigationController(_:animationControllerFor:from:to:) disables the navigation controller's interactive pop gesture recognizer, but setting the gesture's delegate to nil re-enables it.

If you only want the gesture to be enabled in particular circumstances, see this answer.