Media: Crash refreshing media library.

[aerych]

Caught this in the iOS 6s simulator when viewing the media library for a self-hosted blog. There were new items being synced from the blog. The list of thumbs started to refresh, I saw thumbs animate and reorder, I guess making room for a new thumb, then Xcode crashed.

When I tapped on the media library option it reported 10 items. When the crash occured after items reordered it looks like there are 12 counting one "blank" space.

Stacktrace:

2016-10-03 12:06:49.620 WordPress[2503:69964] *** Assertion failure in -[UICollectionView _endItemAnimationsWithInvalidationContext:tentativelyForReordering:animator:], /BuildRoot/Library/Caches/com.apple.xbs/Sources/UIKit_Sim/UIKit-3599.6/UICollectionView.m:5392
2016-10-03 12:06:49.650 WordPress[2503:69964] *** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'attempt to perform an insert and a move to the same index path (<NSIndexPath: 0xc000000000c00016> {length = 2, path = 0 - 6})'
*** First throw call stack:
(
    0   CoreFoundation                      0x0000000113c0434b __exceptionPreprocess + 171
    1   libobjc.A.dylib                     0x000000011366521e objc_exception_throw + 48
    2   CoreFoundation                      0x0000000113c08442 +[NSException raise:format:arguments:] + 98
    3   Foundation                          0x000000010dcd4edd -[NSAssertionHandler handleFailureInMethod:object:file:lineNumber:description:] + 195
    4   UIKit                               0x000000010f5c3f9f -[UICollectionView _endItemAnimationsWithInvalidationContext:tentativelyForReordering:animator:] + 7499
    5   UIKit                               0x000000010f5cf20a -[UICollectionView _endUpdatesWithInvalidationContext:tentativelyForReordering:animator:] + 71
    6   UIKit                               0x000000010f5cf54c -[UICollectionView _performBatchUpdates:completion:invalidationContext:tentativelyForReordering:animator:] + 432
    7   UIKit                               0x000000010f5cf379 -[UICollectionView _performBatchUpdates:completion:invalidationContext:tentativelyForReordering:] + 91
    8   UIKit                               0x000000010f5cf2fb -[UICollectionView _performBatchUpdates:completion:invalidationContext:] + 74
    9   UIKit                               0x000000010f5cf250 -[UICollectionView performBatchUpdates:completion:] + 53
    10  WPMediaPicker                       0x00000001104ba268 __80-[WPMediaCollectionViewController updateDataWithRemoved:inserted:changed:moved:]_block_invoke.179 + 344
    11  UIKit                               0x000000010f5cf052 -[UICollectionView _updateAnimationDidStop:finished:context:] + 2084
    12  UIKit                               0x000000010f5ce58e __71-[UICollectionView _updateWithItems:tentativelyForReordering:animator:]_block_invoke_2 + 82
    13  UIKit                               0x000000010f5a2927 __47-[UICollectionViewAnimation startWithAnimator:]_block_invoke.225 + 295
    14  UIKit                               0x000000010ed23a9e -[UIViewAnimationBlockDelegate _didEndBlockAnimation:finished:context:] + 528
    15  UIKit                               0x000000010ecf6869 -[UIViewAnimationState sendDelegateAnimationDidStop:finished:] + 222
    16  UIKit                               0x000000010ecf6dbe -[UIViewAnimationState animationDidStop:finished:] + 136
    17  QuartzCore                          0x000000010e6a29a8 _ZN2CA5Layer23run_animation_callbacksEPv + 316
    18  libdispatch.dylib                   0x0000000114ae00cd _dispatch_client_callout + 8
    19  libdispatch.dylib                   0x0000000114ac08d6 _dispatch_main_queue_callback_4CF + 406
    20  CoreFoundation                      0x0000000113bc84f9 __CFRUNLOOP_IS_SERVICING_THE_MAIN_DISPATCH_QUEUE__ + 9
    21  CoreFoundation                      0x0000000113b8df8d __CFRunLoopRun + 2205
    22  CoreFoundation                      0x0000000113b8d494 CFRunLoopRunSpecific + 420
    23  GraphicsServices                    0x000000011666ea6f GSEventRunModal + 161
    24  UIKit                               0x000000010ec69f34 UIApplicationMain + 159
    25  WordPress                           0x000000010aea17de main + 62
    26  libdyld.dylib                       0x0000000114b2c68d start + 1
)
libc++abi.dylib: terminating with uncaught exception of type NSException

[aerych]

After removing the blog, and adding it back I saw I had 13 items in the list. Also, the list is apparently haunted: https://cloudup.com/czT8FKz-UYM

[aerych]

Thinking back, I was trying to batch upload 5 images from the camera roll, then disabled wifi in the middle of the upload. Four of the images reported that the internet connection was unavailable, one did not. I assume the upload for the last one had not started. I re-enabled wifi and restarted the uploads for the four. The fifth was then showing a connection timed out message and I restarted it.

Wondering if the crash could be somehow related to the timeout.

[kurzee]

Looks like this is currently only in iOS 10 and is our top crash on Crashlytics.

[kurzee]

@SergioEstevao do you have any insight in to this crash? Since the crash has happened for a number of users, it seems there could be multiple cases of triggering a bad collection update.

[SergioEstevao]

@kurzee I can have a look it could be a bad thread use between the sync in Core Data and the updates in the collection view.

[astralbodies]

I'm been digging into this one further because the crashes continue to pile up. Primarily I think a bulk of the crashes are from calling reloadData in viewDidLoad since the VC itself will do that. May want to defer calling that until after the view appears. I also ran into a bunch of child threads crashing when the remote media library took a while to load and then you switched back to local media.

[astralbodies]

Still only in iOS 10 by the way.

[astralbodies]

Also reported in the Media Picker repo: https://github.com/wordpress-mobile/MediaPicker-iOS/issues/128

[astralbodies]

Closing as I believe this was fixed by #6735.