Navigation stack becomes unusable after canceling

Question

I am running into an issue where my navigation controller becomes unusable after initiating then canceling the new iOS 7 back swipe gesture.

Some relevant information:

• My app has a home page with various activity pages.
• The home page hides the navigation bar in viewWillAppear

• The home page un-hides the navigation bar in viewWillDisappear

  -(void) viewWillAppear:(BOOL)animated
  {
      [super viewWillAppear:animated];
  
      // Let's hide the navbar when we show the home view
      [self.navigationController setNavigationBarHidden:YES];
      …
  }
  
  -(void) viewDidDisappear:(BOOL)animated 
  {
      [super viewDidDisappear:animated];
  
      // Let's hide the navbar when we show the home view
      [self.navigationController setNavigationBarHidden:NO];
  }
  

When a user taps a activity icon on the home page the view controller for the activity is pushed onto the stack.

If a user starts to use the new back swipe gesture in iOS but then stops the gesture (i.e. decides not to go back) everything looks ok. However, if a user causes another view controller to get pushed on the nav stack the nag bar then becomes unusable and the user can not navigate back from the current view controller.

Notes

• It only happens when I show/hide the navigation bar
• I can still slowly perform the back gesture and everything will work fine as long as I don't cancel the gesture
• The nav bar seems like it will work but hitting the back button doesn't pop the view controller.

Answer 1

Not sure if you already resolved this but I'm facing the same issue but with one difference. The navigation stack only messes up if I setAnimated to NO.

So this works:

[self.navigationController setNavigationBarHidden:YES animated:YES];
...
[self.navigationController setNavigationBarHidden:NO animated:YES];

but this doesn't:

[self.navigationController setNavigationBarHidden:YES animated:NO];
...
[self.navigationController setNavigationBarHidden:NO animated:NO];

If you really want animated to be NO for whatever reason, one work around is to set alpha to 0/1 instead of hiding/unhiding the NavigationBar:

- (void)viewWillAppear:(BOOL)animated {
    [super viewWillAppear:animated];
    self.navigationController.navigationBar.alpha = 0.0f;
}

- (void)viewWillDisappear:(BOOL)animated
{
    [super viewWillDisappear:animated];
    [self.navigationController.navigationBar setAlpha:1.0f];
}

The downside is that there's no nice slide-to-pop transition animation. If you did find a better way, do let us know.

UPDATE: This is now old but I solved my issue by not ensuring that whatever state is changed in current view's viewWillDisappear, is restored in viewWillAppear. Don't tear down things in viewWillDisappear that you can't setup again.

This is what happens when you cancel the pop animation:

---

1. Current viewWillDisappear
2. New viewWillAppear
3. [cancelled... reverses]
4. New viewWillDisappear
5. New viewDidDisappear
6. Current viewWillAppear
7. Current viewDidAppear

---

I guess in this brave new world, viewWillDisappear/viewWillAppear does not always mean view "will" disappear/appear :)

Answer 2

I was able to resolve this issue by using animated: true in viewWillAppear and animated: false in viewWillDisappear of the 2nd view controller

Answer 3

I had the same problem, and after searching around, it looks like you can't get a notification if the gesture is cancelled. There is no -shouldCancel on the gesture recognizer delegate, and there is no -willReshowViewController on the navigation controller. So I have the view controller that needs the navigation bar shown (i.e. the controller that is being cancelled on) set self.navigationController.navigationBarHidden = NO in -viewWillAppear. That way when the gesture is cancelled and -viewWillAppear is called, the navigation bar will be unhidden again. As far as I can tell, this is the only way to have both the swipe-back gesture and shown/hidden navigation bars without a problem when cancelling the gesture.

Answer 4

Its will help you to avoid freezing the app.

- (void)navigationController:(UINavigationController *)navigationController
       didShowViewController:(UIViewController *)viewController
                    animated:(BOOL)animate
{
    if ([self.navigationController respondsToSelector:@selector(interactivePopGestureRecognizer)])
    {
        if (self.navigationController.viewControllers.count > 1)
        {
            self.navigationController.interactivePopGestureRecognizer.enabled = YES;
        }
        else
        {
            self.navigationController.interactivePopGestureRecognizer.enabled = NO;
        }
    }
}

Answer 5

I think my solution may help you.

Let's assume that the class of your homepage view controller is HomePageViewController(class name), and the activity view controller is called ActivityViewController(class name, too)

First, in your HomePageViewController's viewWillAppear:

- (void)viewWillAppear:(BOOL)animated
{
    [super viewWillAppear:animated];
    [self.navigationController setNavigationBarHidden:YES];
}

Secondly, in your ActivityViewController, add these codes:

- (void)viewWillAppear:(BOOL)animated
{
    [super viewWillAppear:animated];
    [self.navigationController setNavigationBarHidden:NO animated:YES];
}

- (void)viewWillDisappear:(BOOL)animated
{
    //trick to fix navigationbar disappear problem that when UIScreenEdgePanGesture is happening.
    if ([self.navigationController.topViewController isKindOfClass:[HomePageViewController class]]) {
        [self.navigationController setNavigationBarHidden:YES animated:YES];
    } else {
        [self.navigationController setNavigationBarHidden:NO animated:YES];
    }
    [super viewWillDisappear:animated];
}