Very quick swipes cause app to freeze

[jyc66]

On iOS 12.0.1, iPhone X with SwipeableTabBarController 1.4.0. Initially, produced in my app and then reproduced on the sample app.

Issue: Swipe very quick (velocity.x > 1500, even up to 4000) causes the app to sometime freeze. The tabs may still work (they select but nothing else changes).

Reproduction steps:

1. Make this change in the sample app to make it easier to reproduce:
   In TabBarController.swift, line 17, change selectedViewController = viewControllers![1] to selectedViewController = viewControllers![0]

2. Run the app on a real device

3. Slowly swipe from right to left so that the screen tracks your finger.

4. From the middle screen, very quickly swipe from right to left. You need to be quick enough so that the tab changes without tracking your finger. It seems to happen most often when velocity.x is over 1500.

5. If the bug does not occur, you must kill the app and restart as the issue will not occur once each screen has been displayed.

I have not been able to fix this myself as of yet but I have noticed that UIView.animate has been called and the completion handler is never fired when the issue occurs.

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[marcosgriselli]

I've been fighting this issue since the release of the library. It happens because it is trying to start a transition before the previous one finished. I'll see if I can come up with a final solution on the upcoming days.

[jyc66]

Thanks, one note is that if the view has already appeared I haven't been able to reproduce the issue. Ie it can only happen the first time you swipe to a particular tab.

[VitaliyR]

Wouch saw it also. Reproducible simple without changing library code - just be fast enough (even on the simulator using a trackpad)

[marcosgriselli]

Just spent some time digging into this and I gotta admit this issue is strange. All the steps seem to be executed correctly but the transition simply doesn't happen. I'll take some time closer to the end of the week or weekend to refactor a few implementations that should fix this.

[jyc66]

Looking forward to it, let me know if I can help. (Admittedly, I already spent a bit of time and could not solve it myself)

[jyc66]

Hello @marcosgriselli did you end up looking at this issue this weekend?

[marcosgriselli]

@jyc66 Hey! good news I'm about to finish refactoring a lot of the transition behavior based on some Apple sample code which I believe works fine. Are you using an animation other than sideBySide? I still need to adjust the frames set up for all the different supported animations.

[marcosgriselli]

You can check the refactor branch momentarily although it is missing some features that will get added on the upcoming days.

[jyc66]

Hey this is great, I'll check tomorrow when I'm at the office. Thanks

[marcosgriselli]

@jyc66 perfect, let me know how it goes. There are some features still missing like completing the transition when you flick quickly but it shouldn't be too hard to add.

[jyc66]

I tried it out yesterday using the example app and wasn't able to reproduce the issue however in my actual app I end up with a crash on load. I haven't had a chance to investigate the cause. Our app is rather complicated and has a lot of legacy code so I'm not sure where the issue lies. I'll spend a bit more time later this week on it. Thanks

[marcosgriselli]

Ok, keep me posted on that

[marcosgriselli]

@jyc66 did you had any luck with finding the crash origin?