unwind with custom segue on UINavigationController pop via "back" button

Question

Simple storyboard setup: UIViewController with UINavigationController. On a table cell click a custom segue pushes a new UIViewController onto the navigation stack. All good. But then pressing the "back" button in the navigation bar, it only uses the default pop animation.

How do I tell the navigation controller to use my custom segue when popping back? I've added

- (UIStoryboardSegue *)segueForUnwindingToViewController:(UIViewController *)toViewController fromViewController:(UIViewController *)fromViewController identifier:(NSString *)identifier

- (BOOL)canPerformUnwindSegueAction:(SEL)action fromViewController:(UIViewController *)fromViewController withSender:(id)sender

to both view controllers but they don't get called at all.

What am I missing?

Answer 1

You can accomplish this by creating a custom transition instead of using a custom segue. It took me a while to understand, but it is basically very simple. Just make sure that your first view controller adopts the UINavigationControllerDelegate protocol. Then, still in the first view controller, implement the following method:

- (id<UIViewControllerAnimatedTransitioning>)navigationController:(UINavigationController *)navigationController
                              animationControllerForOperation:(UINavigationControllerOperation)operation
                                           fromViewController:(UIViewController *)fromVC
                                             toViewController:(UIViewController *)toVC
{
return X // where X is an animation Controller object, an instance of the animator class.  
}

Still in the first view controller, for example in ViewDidLoad, tell the navigationcontroller that the first view controller will act as its delegate:

self.navigationController.delegate = self;

Last but not least, create an animator class that adopts the UIViewControllerAnimatedTransitioning protocol. Implement the following methods:

- (void)animateTransition:(id<UIViewControllerContextTransitioning>)transitionContext

and

- (NSTimeInterval)transitionDuration:(id<UIViewControllerContextTransitioning>)transitionContext

The first method holds the transition code. This transition code will automatically be used when tapped on the back button.

Here is a very simple example project.