viewWillDisappear: Determine whether view controller is being popped or is showing a sub-view controller

Question

You can use the following.

- (void)viewWillDisappear:(BOOL)animated {
  [super viewWillDisappear:animated];
  NSArray *viewControllers = self.navigationController.viewControllers;
  if (viewControllers.count > 1 && [viewControllers objectAtIndex:viewControllers.count-2] == self) {
    // View is disappearing because a new view controller was pushed onto the stack
    NSLog(@"New view controller was pushed");
  } else if ([viewControllers indexOfObject:self] == NSNotFound) {
    // View is disappearing because it was popped from the stack
    NSLog(@"View controller was popped");
  }
}

This is, of course, possible because the UINavigationController's view controller stack (exposed through the viewControllers property) has been updated by the time that viewWillDisappear is called.

I think the easiest way is:

 - (void)viewWillDisappear:(BOOL)animated
{
    if ([self isMovingFromParentViewController])
    {
        NSLog(@"View controller was popped");
    }
    else
    {
        NSLog(@"New view controller was pushed");
    }
    [super viewWillDisappear:animated];
}

Swift:

override func viewWillDisappear(animated: Bool)
{
    if isMovingFromParent
    {
        print("View controller was popped")
    }
    else
    {
        print("New view controller was pushed")
    }
    super.viewWillDisappear(animated)
}

From Apple's Documentation in UIViewController.h :

"These four methods can be used in a view controller's appearance callbacks to determine if it is being presented, dismissed, or added or removed as a child view controller. For example, a view controller can check if it is disappearing because it was dismissed or popped by asking itself in its viewWillDisappear: method by checking the expression ([self isBeingDismissed] || [self isMovingFromParentViewController])."

- (BOOL)isBeingPresented NS_AVAILABLE_IOS(5_0);

- (BOOL)isBeingDismissed NS_AVAILABLE_IOS(5_0);

- (BOOL)isMovingToParentViewController NS_AVAILABLE_IOS(5_0);

- (BOOL)isMovingFromParentViewController NS_AVAILABLE_IOS(5_0);

So yes, the only documented way to do this is the following way :

- (void)viewWillDisappear:(BOOL)animated
{
    [super viewWillDisappear:animated];
    if ([self isBeingDismissed] || [self isMovingFromParentViewController]) {
    }
}

Swift 3 version:

override func viewWillDisappear(_ animated: Bool) {
    super.viewWillDisappear(animated)
    
    if self.isBeingDismissed || self.isMovingFromParentViewController { 
    }
}

If you just want to know whether your view is getting popped, I just discovered that self.navigationController is nil in viewDidDisappear, when it is removed from the stack of controllers. So that's a simple alternative test.

(This I discover after trying all sorts of other contortions. I'm surprised there's no navigation controller protocol to register a view controller to be notified on pops. You can't use UINavigationControllerDelegate because that actually does real display work.)

Swift 4

override func viewWillDisappear(_ animated: Bool)
    {
        if self.isMovingFromParent
        {
            //View Controller Popped
        }
        else
        {
            //New view controller pushed
        }
       super.viewWillDisappear(animated)
    }

In Swift:

 override func viewWillDisappear(animated: Bool) {
    if let navigationController = self.navigationController {
        if !contains(navigationController.viewControllers as! Array<UIViewController>, self) {
        }
    }

    super.viewWillDisappear(animated)

}

I find Apple's documentation on this is hard to understand. This extension helps see the states at each navigation.

extension UIViewController {
    public func printTransitionStates() {
        print("isBeingPresented=\(isBeingPresented)")
        print("isBeingDismissed=\(isBeingDismissed)")
        print("isMovingToParentViewController=\(isMovingToParentViewController)")
        print("isMovingFromParentViewController=\(isMovingFromParentViewController)")
    }
}