Open Radar

 
Summary:
When a interactive transition that was initiated by updating the view controller stack using UINavigationController's setViewControllers:animated: is cancelled, the view controller stack is not restored to the state before the setViewControllers:animated:.

Steps to Reproduce:
1. Present a nav controller with a root controller
2. Use setViewControllers:animated: to replace the top view controller with animated set to YES
3. Have the nav controller delegate return a animation controller and interaction controller (i.e. the transition is interactive)
4. Make the interaction controller cancel the transition

Expected Results:
The view controller stack (navigationController.viewControllers) is restored to how it was before the setViewControllers:animated: call, with the original root controller as the top view controller.

Actual Results:
The view controller stack now has both the original root view controller and the view controller that we set as its replacement. The stack height increased by 1.

Regression: N/A

Notes:
A workaround is to remove the second view controller when the transition cancels. I solved it by using the second view controller transitionCoordinator's notifyWhenInteractionEndsUsingBlock:. See for example the implementation of a method that replaces the top view controller:

`- (void) replaceTopViewController: (UIViewController *) viewController animated: (BOOL) animated
{
    // setViewControllers:animated:YES is currently buggy in iOS 7 beta. See e.g. https://devforums.apple.com/message/861601
    
    NSMutableArray *viewControllers = [NSMutableArray arrayWithArray: self.viewControllers];

    UIViewController *originalTopViewController = [viewControllers lastObject];
    
    [viewControllers replaceObjectAtIndex:viewControllers.count-1 withObject:viewController];
    [self setViewControllers:viewControllers animated:animated];
    
    [viewController.transitionCoordinator notifyWhenInteractionEndsUsingBlock:^(id<UIViewControllerTransitionCoordinatorContext> context) {
        if ([context isCancelled]) { // when the transition is cancelled, the to vc is unfortunately not removed by the navigation controller
            [self popViewControllerAnimated: NO];
            [self pushViewController:originalTopViewController animated:NO];
        }
    }];
}`

I would expect that the last lines (starting with [viewController.transitionCoordinator...) would not be necessary.