UIKitCore Crash When Entering Foreground

Question

Hey friends, I have a crash that's been plaguing me for some time now that I've made no progress on, so I'm throwing a hail-mary here.General information:- This stack trace is taken from Fabric/Firebase.- It is only happening on iOS13, across all versions of iOS 13 that appear active for our users, from 13.1.3 up to and including 13.3.0- It's happening to all live versions of our application that support iOS 13 (it is affecting versions that were released before iOS 13 came out, so it's not something we introduced recently)- It has impacted around 10k of our users in the last month and is by far the most prevalent crash we're experiencing.- The app is a messaging app- Though the stack trace includes a lot of scene delegate frames, our app has not implemented a UISceneDelegate, everything still goes through our UIAppDelegate implementation only.Debugging Information:- I've been unable to reproduce the crash, either with the live AppStore build or running locally through Xcode on device or simulator- I've set symbolic breakpoint on -[UIView(Internal) _addSubview:positioned:relativeTo:], which is called a ton, but haven't seen a stack trace with similar elements to the stack trace of this crash when resuming the app from background.- Since the symbolic breakpoint is set on an internal function, I'm unaware of any logging I could include to gain additional information- The last (or nearly last) entry in our crash logging is a record of applicationDidEnterBackground: being called, so I initially assumed the app was simply crashing in the background, but then noticed that each of the stack traces include -[UIApplication _sendWillEnterForegroundCallbacks], so I'm led to believe that this is happening when the user resumes the app from a backgrounded state.I generally understand what the crash code means and that objc_msgSend means a message is being sent to a deallocated object, but without being able to reproduce I don't know of any course of action I can take to move towards resolving this. Any clues or pointers or information or ideas you might have would be greatly appreciated. Cheers.Stack Trace:Crashed: com.apple.main-threadEXC_BAD_ACCESS KERN_INVALID_ADDRESS 0x0000000000000010Crashed: com.apple.main-thread0  libobjc.A.dylib                0x18325cfb0 objc_msgSend + 161  UIKitCore                      0x187ae2ba0 -[UIView(Internal) _addSubview:positioned:relativeTo:] + 5402  UIKitCore                      0x18741c61c -[UIInputWindowController changeToInputViewSet:] + 16563  UIKitCore                      0x18741d0d4 __43-[UIInputWindowController setInputViewSet:]_block_invoke + 644  UIKitCore                      0x187adbfc0 +[UIView(Animation) performWithoutAnimation:] + 1045  UIKitCore                      0x18741cdd8 -[UIInputWindowController setInputViewSet:] + 7326  UIKitCore                      0x187417358 -[UIInputWindowController performOperations:withAnimationStyle:] + 607  UIKitCore                      0x1871325c4 -[UIInputResponderController setKeyWindowSceneInputViews:animationStyle:] + 21848  UIKitCore                      0x187131d14 -[UIInputResponderController setInputViews:animationStyle:] + 2169  UIKitCore                      0x1871343b4 -[UIInputResponderController forceOrderOutAutomaticExceptAccessoryView] + 48410 UIKitCore                      0x1879ff32c -[UIKeyboardAutomatic willResume:] + 73211 Foundation                     0x18391306c __57-[NSNotificationCenter addObserver:selector:name:object:]_block_invoke_2 + 2812 CoreFoundation                 0x1834a099c __CFNOTIFICATIONCENTER_IS_CALLING_OUT_TO_AN_OBSERVER__ + 2813 CoreFoundation                 0x1834a09ec ___CFXRegistrationPost1_block_invoke + 6814 CoreFoundation                 0x18349fce4 _CFXRegistrationPost1 + 39615 CoreFoundation                 0x18349f97c ___CFXNotificationPost_block_invoke + 10816 CoreFoundation                 0x183418910 -[_CFXNotificationRegistrar find:object:observer:enumerator:] + 142417 CoreFoundation                 0x18349f2ac _CFXNotificationPost + 126818 Foundation                     0x183801bfc -[NSNotificationCenter postNotificationName:object:userInfo:] + 6419 UIKitCore                      0x18764d06c -[UIApplication _sendWillEnterForegroundCallbacks] + 28420 UIKitCore                      0x186dce420 __101-[_UISceneLifecycleMultiplexer _evalTransitionToSettings:fromSettings:forceExit:withTransitionStore:]_block_invoke_2 + 178021 UIKitCore                      0x18727e9f8 _UIScenePerformActionsWithLifecycleActionMask + 11222 UIKitCore                      0x186dcdc90 __101-[_UISceneLifecycleMultiplexer _evalTransitionToSettings:fromSettings:forceExit:withTransitionStore:]_block_invoke + 21223 UIKitCore                      0x186dcd6c0 -[_UISceneLifecycleMultiplexer _performBlock:withApplicationOfDeactivationReasons:fromReasons:] + 30424 UIKitCore                      0x186dcdaac -[_UISceneLifecycleMultiplexer _evalTransitionToSettings:fromSettings:forceExit:withTransitionStore:] + 75225 UIKitCore                      0x186dcd330 -[_UISceneLifecycleMultiplexer uiScene:transitionedFromState:withTransitionContext:] + 34026 UIKitCore                      0x186dd1ab0 __186-[_UIWindowSceneFBSSceneTransitionContextDrivenLifecycleSettingsDiffAction _performActionsForUIScene:withUpdatedFBSScene:settingsDiff:fromSettings:transitionContext:lifecycleActionType:]_block_invoke_2 + 19627 UIKitCore                      0x18729887c ___UISceneSettingsDiffActionPerformChangesWithTransitionContext_block_invoke + 2828 UIKitCore                      0x1871aac9c +[BSAnimationSettings(UIKit) tryAnimatingWithSettings:actions:completion:] + 86829 UIKitCore                      0x187298834 _UISceneSettingsDiffActionPerformChangesWithTransitionContext + 26030 UIKitCore                      0x186dd17c8 __186-[_UIWindowSceneFBSSceneTransitionContextDrivenLifecycleSettingsDiffAction _performActionsForUIScene:withUpdatedFBSScene:settingsDiff:fromSettings:transitionContext:lifecycleActionType:]_block_invoke + 15231 UIKitCore                      0x18729871c _UISceneSettingsDiffActionPerformActionsWithDelayForTransitionContext + 10832 UIKitCore                      0x186dd1624 -[_UIWindowSceneFBSSceneTransitionContextDrivenLifecycleSettingsDiffAction _performActionsForUIScene:withUpdatedFBSScene:settingsDiff:fromSettings:transitionContext:lifecycleActionType:] + 39233 UIKitCore                      0x186c399a0 __64-[UIScene scene:didUpdateWithDiff:transitionContext:completion:]_block_invoke + 64034 UIKitCore                      0x186c38464 -[UIScene _emitSceneSettingsUpdateResponseForCompletion:afterSceneUpdateWork:] + 25635 UIKitCore                      0x186c396d0 -[UIScene scene:didUpdateWithDiff:transitionContext:completion:] + 23636 UIKitCore                      0x187632c10 -[UIApplication workspace:didCreateScene:withTransitionContext:completion:] + 56437 UIKitCore                      0x1871ccb9c -[UIApplicationSceneClientAgent scene:didInitializeWithEvent:completion:] + 37638 FrontBoardServices             0x18872ae10 -[FBSSceneImpl _callOutQueue_agent_didCreateWithTransitionContext:completion:] + 45239 FrontBoardServices             0x188751aa0 __86-[FBSWorkspaceScenesClient sceneID:createWithParameters:transitionContext:completion:]_block_invoke.168 + 11640 FrontBoardServices             0x188735ef4 -[FBSWorkspace _calloutQueue_executeCalloutFromSource:withBlock:] + 24041 FrontBoardServices             0x188751734 __86-[FBSWorkspaceScenesClient sceneID:createWithParameters:transitionContext:completion:]_block_invoke + 34442 libdispatch.dylib              0x1831edfd8 _dispatch_client_callout + 2043 libdispatch.dylib              0x1831f0d1c _dispatch_block_invoke_direct + 26444 FrontBoardServices             0x188778254 __FBSSERIALQUEUE_IS_CALLING_OUT_TO_A_BLOCK__ + 4845 FrontBoardServices             0x188777f00 -[FBSSerialQueue _queue_performNextIfPossible] + 43246 FrontBoardServices             0x18877846c -[FBSSerialQueue _performNextFromRunLoopSource] + 3247 CoreFoundation                 0x1834c4108 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ + 2848 CoreFoundation                 0x1834c405c __CFRunLoopDoSource0 + 8449 CoreFoundation                 0x1834c37c8 __CFRunLoopDoSources0 + 18450 CoreFoundation                 0x1834be694 __CFRunLoopRun + 106851 CoreFoundation                 0x1834bdf40 CFRunLoopRunSpecific + 48052 GraphicsServices               0x18d73b534 GSEventRunModal + 10853 UIKitCore                      0x187636a60 UIApplicationMain + 194054 Remind101                      0x10232aa8c main + 16 (main.m:16)55 libdyld.dylib                  0x18333ce18 start + 4(16 other threads appear dormant)

ptsochantaris · Answer

We&#x27;ve been seeing this too - it&#x27;s the number one crash in our app currently. I created a thread about it  while back here:https://forums.developer.apple.com/message/392520#392520There are also threads about this issue that are very likely either related or the same problem, here:https://forums.developer.apple.com/message/386327#386327https://forums.developer.apple.com/message/401926#401926And there are probably more... I created a DTS request about it a while ago, Apple just refunded the DTS credit for it and pasted some generic copy about using Xcode bug tools to diagnose the (so far locally unreproducable) issue.I really wish someone would look into it because like I said it&#x27;s the #1 crash in our app, it feels like an iOS bug, and any hints on how it could be worked-around would be super-helpful...

ptsochantaris · Answer

Just to add, our experience matches almost exactly the points you describe, the points which coincide:- It is only happening on iOS13, across all versions of iOS 13 that appear active for our users, from 13.2.0 and up- It&#x27;s happening to all live versions of our application that support iOS 13 (it is affecting versions that were released before iOS 13 came out, so it&#x27;s not something we introduced recently)- Though the stack trace includes a lot of scene delegate frames, our app has not implemented a UISceneDelegate, everything still goes through our UIAppDelegate implementation only

ptsochantaris · Answer

Have filed radar FB7562386 in case it also catched someone&#x27;s eye on a tech team.

meccatol6 · Answer

We have the same problems in our project.I guess it&#x27;s because we used &#x27;inputAccessoryView&#x27; wrong way.I used it by method override. In that method, I checked some cconditions for returning inputAccessoryView.Depends on the condition, it returned inputAccessoryView or nil.Another VC that uses inputAccessoryView in our app is not making the crash.If you want to reproduce that crash, just tap textview or textfield that shown with inputAccessoryView, and then change iPhone status to multi-tasking mode and slide up your app for terminating.I could reproduce that crashes on my phone.We&#x27;ll change the usage of this way to fix the crash.I hope this will be helpful.