ios - Invalid parameter exception thrown by _UIQueuingScrollView

Question

My app that contains a UITableViewController embedded in UIPageViewController raises this exception from time to time:

Invalid parameter not satisfying: [views count] == 3

Backtrace:

* thread #1: tid = 0x6239fa, 0x03d1d88a libobjc.A.dylib`objc_exception_throw, queue = 'com.apple.main-thread, stop reason = breakpoint 25.3
    frame #0: 0x03d1d88a libobjc.A.dylib`objc_exception_throw
    frame #1: 0x0404f448 CoreFoundation`+[NSException raise:format:arguments:] + 136
    frame #2: 0x03428fee Foundation`-[NSAssertionHandler handleFailureInMethod:object:file:lineNumber:description:] + 116
    frame #3: 0x01e7c535 UIKit`-[_UIQueuingScrollView _replaceViews:updatingContents:adjustContentInsets:animated:] + 185
    frame #4: 0x01e800ca UIKit`-[_UIQueuingScrollView _didScrollWithAnimation:force:] + 1231
    frame #5: 0x01e7bb57 UIKit`-[_UIQueuingScrollView _scrollViewAnimationEnded:finished:] + 104
    frame #6: 0x0190583c UIKit`-[UIScrollView(UIScrollViewInternal) animator:stopAnimation:fraction:] + 62
    frame #7: 0x0197096e UIKit`-[UIAnimator stopAnimation:] + 533
    frame #8: 0x0197100a UIKit`-[UIAnimator(Static) _advanceAnimationsOfType:withTimestamp:] + 325
    frame #9: 0x01970b76 UIKit`-[UIAnimator(Static) _LCDHeartbeatCallback:] + 67
    frame #10: 0x01663b8a QuartzCore`CA::Display::DisplayLinkItem::dispatch() + 48

    frame #11: 0x01663a46 QuartzCore`CA::Display::DisplayLink::dispatch_items(unsigned long long, unsigned long long, unsigned long long) + 310
    frame #12: 0x01663f6b QuartzCore`CA::Display::TimerDisplayLink::callback(__CFRunLoopTimer*, void*) + 123
    frame #13: 0x0400dbd6 CoreFoundation`__CFRUNLOOP_IS_CALLING_OUT_TO_A_TIMER_CALLBACK_FUNCTION__ + 22
    frame #14: 0x0400d5bd CoreFoundation`__CFRunLoopDoTimer + 1181
    frame #15: 0x03ff5628 CoreFoundation`__CFRunLoopRun + 1816
    frame #16: 0x03ff4ac3 CoreFoundation`CFRunLoopRunSpecific + 467
    frame #17: 0x03ff48db CoreFoundation`CFRunLoopRunInMode + 123
    frame #18: 0x0533b9e2 GraphicsServices`GSEventRunModal + 192
    frame #19: 0x0533b809 GraphicsServices`GSEventRun + 104
    frame #20: 0x01874d3b UIKit`UIApplicationMain + 1225

Does anyone have seen this already or have an idea what the reason could be?

Answer 1

Edit: after using this fix for more time, I can still see the bug on occasion so this isn't the complete fix (well... it was always kind of a hack). I'll update with the actual solution once I'll find it.

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I've encountered this same error using UIPageViewController. After hours debugging the issue, I've found the cause was using UIView animations inside the completion handler of UIPageViewController's setViewControllers:direction:animated:completion:.

I don't know why animating at that stage causes the assertion error (I wasn't animating the UIPageViewController or its child view controllers), but wrapping the code block with dispatch_async on the main queue solves the issue and stop the crashing.