swift - iOS App Freezes on PushViewController

Question

My navigation controller intermittently will freeze on push. It seems to add the new view controller onto the stack, but the animation never takes place. I also have two other containers that hold view controllers on the screen, and I can interact with both of them just fine after the navigation controller freezes. The really interesting thing is if I try to push another view controller onto the navigation controller's stack, I noticed that there is an extra view controller on top of the stack (the view controller that I pushed initially that froze the navigation controller). So if I'm on the home screen (we'll call it VC-Home) and I try to push a new view (VC-1) and it freezes, then I try to push a new view (VC-2), this is what I see in the current stack before the push:

{ [VC-Home, VC-1] }

and after pushViewController is called, it remains the same; VC-2 is not added to the stack.

From what I can tell, the navigation controller starts the animation by making the previous view controller inactive before the animation begins, but then the animation never takes place, leaving the navigation controller in a frozen state.

I'm creating the new view controller from a storyboard by calling UIStoryboard(name: "Main", bundle: nil).instantiateViewControllerWithIdentifier("ViewController") so I don't think there's any issues there. I'm also not overriding pushViewController on the navigation bar. Some unique things about my app is that it is very high-res image heavy (using SDWebImage to manage that) and I always have three containers on the screen at once (one navigation controller, one view controller for search, and one interactive gutter/side/slideout menu).

CPU usage is low and memory usage is normal (steadily around 60-70MB on device when freezes occur).

Are there any ideas with what might be causing this or any debugging tips that could help me discover the real problem?

Update

There's no unique code for the UINavigationController since I'm just pushing using pushViewController(). Here's the code that calls it:

func didSelectItem(profile: SimpleProfile) {
     let vc = UIStoryboard.profileViewController()
     vc.profile = profile
     navigationController?.pushViewController(vc, animated: true)
}

The ViewController that I pushed has the following code in viewDidLoad:

override func viewDidLoad() {
    super.viewDidLoad()
    button.roundView()

    if let type = profile?.profileType {
        //load multiple view controllers into a view pager based on type 
        let viewControllers = ProfileTypeTabAdapter.produceViewControllersBasedOnType(type)
        loadViewPagerViews(viewControllers)

        let topInset = headerView.bounds.height + tabScrollView.contentSize.height
        if let viewPager = viewPager {
            for view in viewPager.views {
                if let tempView = view as? PagingChildViewController {
                    tempView.profile = fullProfile
                    tempView.parentVCDelegate = self
                    tempView.topInset = topInset
                }
            }
        }
    }
}

func loadViewPagerViews(viewControllers: [UIViewController]) {
    viewPager?.views = viewControllers
    viewPager?.delegate = self

    //loading views into paging scroll view (using PureLayout to create constraints)
    let _ = subviews.map { $0.removeFromSuperview() }
    var i = 0
    for item in views {
        addSubview(item.view)
        item.view.autoSetDimensionsToSize(CGSize(width: tabWidth, height: tabHeight))
        if i == 0 {
            item.view.autoPinEdgeToSuperviewEdge(.Leading)
        } else if let previousView = views[i-1].view {
            item.view.autoPinEdge(.Leading, toEdge: .Trailing, ofView: previousView)
        }
        if i == views.count {
            item.view.autoPinEdgeToSuperviewEdge(.Trailing)
        }
        i += 1
    }

    contentSize = CGSize(width: Double(i)*Double(tabWidth), height: Double(tabHeight))
}

Update 2

I finally got it to freeze again. The app was in the background and I brought it back and tried pushing a view controller on the stack when it froze. I noticed an animation was taking place. I have a scrollview at the top of the page that pages through its content every 10 seconds (think of the app stores top banner). On this freeze, I noticed that the banner was mid-animation.

Here's the scrolling function from the my UIScrollView that gets called every 10 seconds:

func moveToNextItem() {
    let pageWidth: CGFloat = CGRectGetWidth(frame)
    let maxWidth: CGFloat = pageWidth * CGFloat(max(images.count, profileImages.count))
    let contentOffset: CGFloat = self.contentOffset.x
    let slideToX = contentOffset + pageWidth

    //if this is the end of the line, stop the timer
    if contentOffset + pageWidth == maxWidth {
        timer?.invalidate()
        timer = nil
        return
    }

    scrollRectToVisible(CGRectMake(slideToX, 0, pageWidth, CGRectGetHeight(frame)), animated: true)
}

I don't recall ever having a push stop because of an animation/scroll taking place, but I could be wrong.

I've also rechecked the stack and the same situation as described above is still the case where [VC-Home, VC-1] is the stack and VC-2 is not pushed on. I've also gone through VC-1's variables and everything has loaded (data calls and image loads).

Update 3

This is getting stranger by the second. I've overriden pushViewController so I can put a breakpoint in there and do some debugging based on Alessandro Ornano's response. If I push a view controller unsuccessfully, then send my app to the background, put a breakpoint into the pushViewController call, and bring the app back, the breakpoint is immediately hit a number of times. If I then continue past all the hits, the next view controller suddenly becomes visible and the last view controller I tried to push is now on the stack as the last view controller. This means that the one that I see is still disabled, which essentially puts me in the same position as before.

Answer 1

We have faced the same problem couple of weeks back. And for our problem we narrowed it down to left-edge pop gesture recogniser. You can try and check if you can reproduce this problem using below steps

• Try using the left edge pop gesture when there are no view controllers below it (i.e on root view controllers, your VC-Home controller)
• Try clicking on any UI elements after this.

If you are able to reproduce the freeze, try disabling the interactivePopGestureRecognizer when the view controller stack have only one view controller.

Refer to this question for more details. Below is the code from the link for ease of reference.

- (void)navigationController:(UINavigationController *)navigationController
   didShowViewController:(UIViewController *)viewController
                animated:(BOOL)animate
{
    if ([self respondsToSelector:@selector(interactivePopGestureRecognizer)])
{
        if (self.viewControllers.count > 1)
        {
            self.interactivePopGestureRecognizer.enabled = YES;
        }
        else
        {
            self.interactivePopGestureRecognizer.enabled = NO;
        }
    }
}