Completion block for popViewController

Question

When dismissing a modal view controller using dismissViewController, there is the option to provide a completion block. Is there a similar equivalent for popViewController?

The completion argument is quite handy. For instance, I can use it to hold off removing a row from a tableview until the modal is off screen, letting the user see the row animation. When returning from a pushed view controller, I would like the same opportunity.

I have tried placing popViewController in an UIView animation block, where I do have access to a completion block. However, this produces some unwanted side effects on the view being popped to.

If there is no such method available, what are some workarounds?

Solution 1

I know an answer has been accepted over two years ago, however this answer is incomplete.

There is no way to do what you're wanting out-of-the-box

This is technically correct because the UINavigationController API doesn't offer any options for this. However by using the CoreAnimation framework it's possible to add a completion block to the underlying animation:

[CATransaction begin];
[CATransaction setCompletionBlock:^{
    // handle completion here
}];

[self.navigationController popViewControllerAnimated:YES];

[CATransaction commit];

The completion block will be called as soon as the animation used by popViewControllerAnimated: ends. This functionality has been available since iOS 4.

Solution 2

Swift 5 version - works like a charm. Based on this answer

extension UINavigationController {
    func pushViewController(viewController: UIViewController, animated: Bool, completion: @escaping () -> Void) {
        pushViewController(viewController, animated: animated)

        if animated, let coordinator = transitionCoordinator {
            coordinator.animate(alongsideTransition: nil) { _ in
                completion()
            }
        } else {
            completion()
        }
    }

    func popViewController(animated: Bool, completion: @escaping () -> Void) {
        popViewController(animated: animated)

        if animated, let coordinator = transitionCoordinator {
            coordinator.animate(alongsideTransition: nil) { _ in
                completion()
            }
        } else {
            completion()
        }
    }
}

Solution 3

I made a Swift version with extensions with @JorisKluivers answer.

This will call a completion closure after the animation is done for both push and pop.

extension UINavigationController {
    func popViewControllerWithHandler(completion: ()->()) {
        CATransaction.begin()
        CATransaction.setCompletionBlock(completion)
        self.popViewControllerAnimated(true)
        CATransaction.commit()
    }
    func pushViewController(viewController: UIViewController, completion: ()->()) {
        CATransaction.begin()
        CATransaction.setCompletionBlock(completion)
        self.pushViewController(viewController, animated: true)
        CATransaction.commit()
    }
}

Solution 4

SWIFT 4.1

extension UINavigationController {
func pushToViewController(_ viewController: UIViewController, animated:Bool = true, completion: @escaping ()->()) {
    CATransaction.begin()
    CATransaction.setCompletionBlock(completion)
    self.pushViewController(viewController, animated: animated)
    CATransaction.commit()
}

func popViewController(animated:Bool = true, completion: @escaping ()->()) {
    CATransaction.begin()
    CATransaction.setCompletionBlock(completion)
    self.popViewController(animated: animated)
    CATransaction.commit()
}

func popToViewController(_ viewController: UIViewController, animated:Bool = true, completion: @escaping ()->()) {
    CATransaction.begin()
    CATransaction.setCompletionBlock(completion)
    self.popToViewController(viewController, animated: animated)
    CATransaction.commit()
}

func popToRootViewController(animated:Bool = true, completion: @escaping ()->()) {
    CATransaction.begin()
    CATransaction.setCompletionBlock(completion)
    self.popToRootViewController(animated: animated)
    CATransaction.commit()
}
}

Solution 5

I had the same issue. And because I had to use it in multiple occasions, and within chains of completion blocks, I created this generic solution in an UINavigationController subclass:

- (void) navigationController:(UINavigationController *) navigationController didShowViewController:(UIViewController *) viewController animated:(BOOL) animated {
    if (_completion) {
        dispatch_async(dispatch_get_main_queue(),
        ^{
            _completion();
            _completion = nil;
         });
    }
}

- (UIViewController *) popViewControllerAnimated:(BOOL) animated completion:(void (^)()) completion {
    _completion = completion;
    return [super popViewControllerAnimated:animated];
}

Assuming

@interface NavigationController : UINavigationController <UINavigationControllerDelegate>

and

@implementation NavigationController {
    void (^_completion)();
}

and

- (id) initWithRootViewController:(UIViewController *) rootViewController {
    self = [super initWithRootViewController:rootViewController];
    if (self) {
        self.delegate = self;
    }
    return self;
}

View more solutions

Comments

[Ben Packard]

I attempted this. I was storing an array of 'deleted row indexes' and whenever the view appears, checking to see if anything needs to be removed. It quickly grew unwieldy but I might give it another shot. I wonder why Apple provide it for one transition but not the other?

[mattjgalloway]

It's only very new on the dismissViewController. Maybe it'll come to popViewController. File a radar :-).

[Ben Packard]

Sure - except then you have to handle all the cases where the view is disappearing for some other reason.

[mattjgalloway]

Seriously though, do file a radar. It's more likely to make it in if people ask for it.

[Ben Packard]

I just tried on bugreport.apple.com - are feature requests some place else?

[mattjgalloway]

That's the right place to ask for it. There's an option for the classification to be 'Feature'.

[Jason Coco]

This answer is not completely correct. While you can't set the new-style block like on -dismissViewController:animated:completionBlock:, but you can get the animation through the navigation controller's delegate. After the animation is complete, -navigationController:didShowViewController:animated: will be called on the delegate and you can do whatever you'd need right there.

[rdelmar]

@BenPackard, yes, and the same is true for putting it in viewDidAppear in the answer you accepted.

[mattjgalloway]

Yep that's true, you could do it in that as well, good point.

[Ben Packard]

Similar limitations though right (e.g. having to test if the animation should fire based on some logic that prevents it in other cases)?

[spstanley]

I really like this solution, I'm going to try it with a category and an associated object.

[k06a]

@spstanley you need to publish this pod :)

[Arbitur]

I put this in an extension of UINavigationController in Swift: extension UINavigationController { func popViewControllerWithHandler(handler: ()->()) { CATransaction.begin() CATransaction.setCompletionBlock(handler) self.popViewControllerAnimated(true) CATransaction.commit() } }

[moger777]

Does not seem to work for me, when I do completionHandler on dismissViewController, the view that was presenting it is part of view hierarchy. When I do the same with the CATransaction, I get a warning that the view is not part of the view hierarchy.

[moger777]

OK, looks like your works if you reverse the begin and completion block. Sorry about the down vote but stack overflow won't let me change :(

[fabb]

Does not work for me on iOS 7, the completion block is called immediately.

[mattjgalloway]

Yeh, while this may work, it's not exactly defined behaviour. You can't rely on this working. popViewControllerAnimated: may dispatch away to somewhere else for example which would stop this from working. It's a great shout though, and if it works on iOS 8, then cool!

[stuckj]

Yeah, this seemed like it would be awesome, but it doesn't appear to work (at least on iOS 8). The completion block is getting called immediately. Likely because of the mixture of core animations with UIView style animations.

[user3344977]

This works for me when pushing a view controller but not when popping on iOS 8. My completion block never fires.

[Julian F. Weinert]

Interesting. For me, in iOS 8.4, the completion block does fire, but approx. half the way down the animation.

[Julian F. Weinert]

For me, in iOS 8.4, written in ObjC the block fires half the way down the animation. Does this really fire in the right moment if written in Swift (8.4)?

[durazno]

THIS DOES NOT WORK

[pronebird]

@rshev why on next runloop?

[rshev]

@Andy from what I remember experimenting with this, something hadn't been propagated yet at that point. Try experimenting with it, love to hear how it works for you.

[pronebird]

@rshev I think I had it the same way before, I have to double check. Current tests run fine.

[Lance Samaria]

@HotJard hello, where would I call this a when popping? I don't want it to trigger until the view has been officially unloaded off the screen by either a right swipe to dismiss or pressing the back button. ViewWillDisappear and ViewDidDisappear gets trigged whenever I switch the views (pressing a diff tabbar button). Any suggestions?

[HotJard]

@LanceSamaria I suggest to use viewDidDisappear. Check if navbar is available, if not – it's not shown in navbar, so it was popped. if (self.navigationController == nil) { trigger your action }

[Dennis]

when you add an alertview or some animation in viewdidload, it will not work immediately

[Bogdan Razvan]

@Arbitur completion block is indeed called after calling popViewController or pushViewController, but if you check what the topViewController is right afterwards, you will notice it is still the old one, just like pop or push never happened...

[Sean]

The accepted answer appears to work in my dev environment with all the emulators/devices I have, but I still get bug reported from production users. Not sure if this will solve the production issue, but let me upvote it just so someone may try it if getting the same issue from the accepted answer.

[Arbitur]

@BogdanRazvan right afterwards what? Does your completion closure get called once the animation is complete?

[kball]

Prematurely added +1. Should be -1. This does not work consistently, which is kind of worse than it not working at all.

[Yogesh Patel]

milions of thanks working for me please note use pushviewcontroller either sometimes it not working :)

[CyberMew]

This does not work if I am using navigationController?.popToRootViewController; it works if I am using navigationController?.popViewController (at least on iOS 13.1).

[Iliyan Kafedzhiev]

Incorrect! It is executed even before viewDidDissapear of the viewController that is poping and can cause a lot of 'hidden' problems if you use it.

[Iliyan Kafedzhiev]

Swift version -> stackoverflow.com/a/60090678/4010725

[leviathan]

Any particular reason why you're calling the completion() async?

[rshev]

when animating with coordinator completion is never executed on the same runloop. this guarantees completion never runs on the same runloop when not animating. it's better to not have this kind of inconsistency.

[Bogdan Razvan]

@Arbitur right after the animation is complete. Yes, the completion closure gets called once the animation is complete, but the topViewController is still the old one, just as it was not yet popped.

[Oliver Pearmain]

While this does work the issue is that it restricts other use of UINavigationControllerDelegate

[Bawenang Rukmoko Pardian Putra]

@HotJard you forgot to add @escaping on the completion handler.

[Leon]

This is not Swift 5, if let where was removed in Swift 3! Also, transitionCoordinator() is wrong, it's a property not a method.

[HotJard]

@Leon thx, updated