Trying to dismiss the presentation controller while transitioning already

Question

I compile my project using Xcode6 GM on iOS8 GM. When dismissing many view controllers, my app always crashes and the debug area shows:

"Trying to dismiss the presentation controller while transitioning already. transitionViewForCurrentTransition is not set, presentation controller was dismissed during the presentation? "

I have googled and find a similar case and shows the same error:

[self.viewController presentViewController:vc animated:NO completion:^{         [self.viewController dismissViewControllerAnimated:NO completion:nil]; }]; 

It works fine using Xcode5 and iOS7 . What does the error means? Is iOS8 isn't happy with the "Hack"? Thanks in advance.

Answer 1

Are you trying to force a device orientation change? Anyway, in my opinion you could try to change your current code to:

[self.navigationController presentViewController:vc animated:NO completion:^{     dispatch_after(0, dispatch_get_main_queue(), ^{         [self.navigationController dismissViewControllerAnimated:NO completion:nil];     }); }]; 

Answer 2

I had the same issue and I found a clean solution avoid using dispatch_async or dispatch_after.

Simply, as described by the exception, you are trying to dismiss a view controller while the presenting transition is still in progress. This means that once the

- presentViewController:animated:completion:  

completion block is called, and you invoke the dismiss, the transitioning is not completed.

Starting from iOS 7 transitioning UIViewController has a new method available

- transitionCoordinator  

The transitionCoordinator gives you the chance to enqueue a completion block as soon as the transition completes.

The object returned by the method conforms the UIViewControllerTransitionCoordinator protocol. Knowing that the solution is really simple.

After the invocation of

- presentViewController:animated:completion:  

the transition coordinator is properly configured by the framework.

Use

- animateAlongsideTransition:completion:  

on it to send the proper completion block.

Here a little code snippet that better explain the solution

void(^completion)() = ^() {     [modalViewController dismissViewControllerAnimated:YES completion:nil]; };  // This check is needed if you need to support iOS version older than 7.0 BOOL canUseTransitionCoordinator = [viewController respondsToSelector:@selector(transitionCoordinator)];  if (animated && canUseTransitionCoordinator) {     [viewController presentViewController:modalViewController animated:animated completion:nil];     [viewController.transitionCoordinator animateAlongsideTransition:nil completion:^(id<UIViewControllerTransitionCoordinatorContext> context) {         completion();     }]; } else {     [viewController presentViewController:modalViewController animated:animated completion:completion]; }