iOS app crashes at tap gesture event

Question

I have a view targeted for iPad that I present modally with modalPresentationStyle property set to UIModalPresentationFormSheet, by pushing firstly its view controller into a navigation controller:

    UINavigationController *navController = [[UINavigationController alloc] initWithRootViewController:myViewController];
    navController.modalTransitionStyle = UIModalTransitionStyleFlipHorizontal;
    navController.modalPresentationStyle = UIModalPresentationFormSheet;
    [self presentViewController:navController animated:YES completion:nil];

Then, in the presented view controller, I want to detect tap gestures outside itself (as I said, I present it as a form sheet), so I have set a tap gesture this way:

- (void)viewDidAppear:(BOOL)animated
{
   [super viewDidAppear:animated];

    self.tapGestureRecognizer = [[UITapGestureRecognizer alloc] initWithTarget:self
                                                                        action:@selector(handleTap:)];

    self.tapGestureRecognizer.numberOfTouchesRequired = 1;
    self.tapGestureRecognizer.numberOfTapsRequired = 1;
    self.tapGestureRecognizer.cancelsTouchesInView = NO;
    [self.view.window addGestureRecognizer:self.tapGestureRecognizer];
}

- (void)handleTap:(UITapGestureRecognizer*)sender
{
   if (sender.state == UIGestureRecognizerStateEnded) {
      CGPoint location = [sender locationInView:nil]; 

      if (![self.view pointInside:[self.view convertPoint:location fromView:self.view.window] withEvent:nil]) {
        [self.view.window removeGestureRecognizer:sender];
        [self dismissModalViewControllerAnimated:YES];
      }
   }
}

The navigation controller I'm presenting modally, and whose root view controller is the one setting this gesture recognizer, displays more views in hierarchy. When only the root view controller is pushed onto the navigation controller stack and I use the tap gesture outside it, it is correctly dismissed and I'm able to present modally this root view controller again. When I navigate from the root view controller and I push one more view controller onto the navigation stack, the tap gesture still works, but then the app crashes when I try to show the form sheet again.

How should I handle this gesture and the behavior I want having a navigation hierarchy?

Thanks in advance

Answer 1

I think your problem is removing the gesture recognizer with self.view.window -- that will be nil when another controller is pushed on the stack, since only the view on screen has a non-nil window property. Try replacing that with [UIApplication sharedApplication].delegate.window and see if that fixes the problem.

Answer 2

One of the possible cause of crash I've encountered is forgetting to declare your view controller as a childViewController to its parent controller.