Open Radar

 
Summary:
With the hidesBarsOnSwipe property set to true on a UINavigationController, we see about 1500-2000 of these crashes per day: http://crashes.to/s/7726b6a2fab

Unfortunately I have not found a way to reproduce the crash, but as you can see in the stack trace, it's all SDK code:

Thread : Fatal Exception: NSInternalInconsistencyException
0  CoreFoundation                 0x00000001824242d8 __exceptionPreprocess
1  libobjc.A.dylib                0x00000001940980e4 objc_exception_throw
2  CoreFoundation                 0x0000000182424198 +[NSException raise:format:]
3  Foundation                     0x00000001832d8ed4 -[NSAssertionHandler handleFailureInMethod:object:file:lineNumber:description:]
4  UIKit                          0x0000000187589a00 -[_UIAnimationCoordinator cancelInteractiveAnimation]
5  UIKit                          0x00000001871d7a18 -[UINavigationController _gestureRecognizedInteractiveHide:]
6  UIKit                          0x0000000187033070 _UIGestureRecognizerSendActions
7  UIKit                          0x0000000186ecc5c4 -[UIGestureRecognizer _updateGestureWithEvent:buttonEvent:]
8  UIKit                          0x000000018733d38c ___UIGestureRecognizerUpdate_block_invoke662
9  UIKit                          0x0000000186e90418 _UIGestureRecognizerRemoveObjectsFromArrayAndApplyBlocks
10 UIKit                          0x0000000186e8e7c4 _UIGestureRecognizerUpdate
11 UIKit                          0x0000000186eca82c -[UIWindow _sendGesturesForEvent:]
12 UIKit                          0x0000000186ec9ee4 -[UIWindow sendEvent:]
13 UIKit                          0x0000000186e9d120 -[UIApplication sendEvent:]
14 UIKit                          0x00000001870d8530 __42-[UIApplication _cancelTouches:withEvent:]_block_invoke
15 UIKit                          0x0000000186f242a0 -[UIApplication _cancelTouches:withEvent:includingGestures:notificationBlock:]
16 UIKit                          0x0000000186f23f90 -[UIApplication _cancelTouches:withEvent:]
17 UIKit                          0x000000018713de94 _UIApplicationHandleEventFromQueueEvent
18 UIKit                          0x0000000186e9b634 _UIApplicationHandleEventQueue
19 CoreFoundation                 0x00000001823dc240 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__
20 CoreFoundation                 0x00000001823db59c __CFRunLoopDoSources0
21 CoreFoundation                 0x00000001823d9594 __CFRunLoopRun
22 CoreFoundation                 0x00000001823052d4 CFRunLoopRunSpecific
23 GraphicsServices               0x000000018bd636fc GSEventRunModal
24 UIKit                          0x0000000186f02f40 UIApplicationMain
25 Team Stream                    0x0000000100047480 main (main.m:13)
26 libdyld.dylib                  0x0000000194742a08 start

Steps to Reproduce:
Create a UINavigationController with a UIScrollView and enable hidesBarsOnSwipe (sample project attached).

Not sure if this is related, but in viewWillAppear: for the controller at the bottom of the navigation stack, we set hidesBarsOnScroll to true. In viewWillAppear: for other controllers pushed on top of it, we set it to false. So we only hide bars when scrolling the root view controler.

Expected Results:
Given that it's all UIKit code, I would expect the invalid state to be a no-op, perhaps logged to the console.

Actual Results:
UIKit raises an exception and crashes the process

Version:
iOS 8+

Notes:
This crash also occurs in iOS 9. 



Configuration:
Occurs on iPhone, iPod Touch and iPad

Attachments:
'HideBarsOnSwipeCrash.zip' was successfully uploaded.