Container view disappearing on completeTransition:

Question

I am using custom view controller transitions, UIViewControllerAnimatedTransitioning, to present and dismiss a view controller.

The presenting animation works fine, but when I run the dismiss animation, once I call completeTransition: the containerView gets removed.

I'm not sure what is going on, here is the transition code:

- (void)animateTransition:(id<UIViewControllerContextTransitioning>)transitionContext {
    UIViewController *fromViewController = [transitionContext viewControllerForKey:UITransitionContextFromViewControllerKey];
    UIViewController *toViewController = [transitionContext viewControllerForKey:UITransitionContextToViewControllerKey];

    UIView *containerView = [transitionContext containerView];
    containerView.backgroundColor = [UIColor blackColor];

    if (self.reverse) {
        [containerView addSubview:toViewController.view];
        [containerView addSubview:fromViewController.view];
    } else {
        [containerView addSubview:fromViewController.view];
        [containerView addSubview:toViewController.view];
    }

    if (! self.reverse) { // Forward
        toViewController.view.frame = CGRectMake(-containerView.frame.size.width, 0, containerView.frame.size.width, containerView.frame.size.height);
    } else {
        fromViewController.view.frame = CGRectMake(0, 0, containerView.frame.size.width, containerView.frame.size.height);
    }

    [UIView animateWithDuration:[self transitionDuration:transitionContext] delay:0 usingSpringWithDamping:0.75f initialSpringVelocity:1.0f options:UIViewAnimationOptionCurveLinear animations:^{
        if (self.reverse) {
            fromViewController.view.frame = CGRectMake(-containerView.frame.size.width, 0, containerView.frame.size.width, containerView.frame.size.height);
            fromViewController.view.layer.opacity = 0.f;
            toViewController.view.layer.opacity = 1.f;
        } else {
            toViewController.view.frame = CGRectMake(0, 0, containerView.frame.size.width, containerView.frame.size.height);
            toViewController.view.layer.opacity = 1.f;
            fromViewController.view.layer.opacity = 0.3f;
        }
    } completion:^(BOOL finished) {
        [transitionContext completeTransition:finished];
    }];
}

- (NSTimeInterval)transitionDuration:(id<UIViewControllerContextTransitioning>)transitionContext {
    if (self.reverse) {
        return 0.45;
    } else {
        return 0.35;
    }
}

How can I prevent my toViewController from disappearing if .reverse is set to YES?

Update: This is how I'm presenting the view controller:

SecondaryViewController *vc = [[SecondaryViewController alloc] init];
UINavigationController *navigationController = [[UINavigationController alloc] initWithRootViewController:vc];
navigationController.modalPresentationStyle = UIModalPresentationCustom;
navigationController.transitioningDelegate = self;
[self presentViewController:navigationController animated:YES completion:nil];

Answer 1

The container view disappearing on dismissal is correct behavior. Your mistake is adding the fromView to it.

You are incorrectly distinguishing whether this is presentation or dismissal and what you should do in each case. Simply use the two view controllers fromViewController and toViewController to tell them apart; on dismissal, the roles are reversed. On dismissal, do not add anything to the content view; the original presenter is still present and will be revealed by the removal of the container view.

So, on presentation, add only the toView to the container view. On dismissal, do not add anything to the container view. It's as simple as that.