iOS 7 custom transition glitch

Question

This video shows the issue I am having. http://www.youtube.com/watch?v=C9od_2KZAbs

I am attempting to create a custom push interactive transition using a UIPanGestureRecognizer. I have an interactive transition delegate (using UIPercentDrivenInteractiveTransition) and a transition animator.

Here is how the pan gesture controls the transition:

- (void) panGestureRecognized:(UIPanGestureRecognizer *) gestureRecogznier {

    CGPoint translation = [gestureRecogznier translationInView:gestureRecogznier.view];

    if (gestureRecogznier.state == UIGestureRecognizerStateBegan) {

        self.interactiveTransitionAnimator = [[UIPercentDrivenInteractiveTransition alloc] init];

        EVDetailViewController *detailViewController = [self.storyboard instantiateViewControllerWithIdentifier:@"EVDetailViewController"];
        [self.navigationController pushViewController:detailViewController animated:YES];
    }
    else if (gestureRecogznier.state == UIGestureRecognizerStateChanged) {

        CGFloat d = (translation.x / CGRectGetWidth(self.view.bounds)) * -1;
        [self.interactiveTransitionAnimator updateInteractiveTransition:d];
    }
    else if (gestureRecogznier.state == UIGestureRecognizerStateEnded) {

        if ([gestureRecogznier velocityInView:self.view].x < 0) {
            [self.interactiveTransitionAnimator finishInteractiveTransition];
        } else {
            [self.interactiveTransitionAnimator cancelInteractiveTransition];
        }

        self.interactiveTransitionAnimator = nil;
    }
}

The UINavigationControllerDelegate handles the vending of both transition delegate objects, which is triggered when pushViewController: is called.

The transition animator has a very simple animation:

- (void)animateTransition:(id<UIViewControllerContextTransitioning>)transitionContext {

    UIViewController* toViewController = [transitionContext viewControllerForKey:UITransitionContextToViewControllerKey];
    [[transitionContext containerView] addSubview:toViewController.view];

    CGRect finalToVCFrame = [transitionContext finalFrameForViewController:toViewController];

    if (self.operation == UINavigationControllerOperationPush) {

        // set offscreen to the right
        toViewController.view.frame = CGRectMake(320.0f, 0.0f, 320.0f, 568.0f);

        [UIView animateWithDuration:[self transitionDuration:transitionContext] delay:0.0f options:0 animations:^{

            toViewController.view.frame = finalToVCFrame;

        } completion:^(BOOL finished) {

            // *** When this is called, the glitch occurs
            [transitionContext completeTransition:YES];
        }];
    }
}

In the video, the pan gesture ends about 60% of the way through, which triggers the finishInteractiveTransition call. Everything goes smoothly until the completion block in the UIView block-based animation calls completeTransition:. When this method is called, the toViewController re-animates the last part of the push animation unnecessarily. In the video the red view is the window. The animation duration is 3 seconds.

I cannot figure out why this happens. It looks like the animation between the point when the gesture ends and when completeTransition: is called happens twice. Any ideas?

Answer 1

Or, as matt observed here, you can also either defer the completeTransition or drive the custom interaction controller yourself:

I've seen something similar. I have two possible workarounds. One is to use delayed performance in the animation completion handler:

   } completion:^(BOOL finished) {
            double delayInSeconds = 0.1;
            dispatch_time_t popTime = 
                 dispatch_time(DISPATCH_TIME_NOW, (int64_t)(delayInSeconds * NSEC_PER_SEC));
            dispatch_after(popTime, dispatch_get_main_queue(), ^(void){
                BOOL cancelled = [transitionContext transitionWasCancelled];
                [transitionContext completeTransition:!cancelled];
            });
           self.interacting = NO;
    }];

The other possibility is: don't use percent-drive animation! I've never had a problem like this when driving the interactive custom animation myself manually.

Answer 2

As of iOS 7.1, I can reproduce this in simulator but not on an actual device. Anyway, there appears to be a workaround:

self.interactiveTransitionAnimator.completionSpeed = 0.999;

There is a radar for this bug: rdar://14675246