Crash when presenting a ViewController from modally presented ViewController - ios

Question

In our production app we do have crash reports on presenting a ViewController from a modally presented `ViewController.
We have a BackgroundForegroundDelegate. Whenever the app enters the background it'll present a Lockscreen on top of the current ViewController.
AppDelegate:
func applicationDidEnterBackground(_ application: UIApplication) {
backgroundForegroundDelegate?.applicationDidEnterBackground()
}
func applicationWillEnterForeground(_ application: UIApplication) {
backgroundForegroundDelegate?.applicationWillEnterForeground()
}
LockScreenViewController:
class LockScreenViewController: UIViewController {
override func viewDidLoad() {
super.viewDidLoad()
let blurEffectView = UIVisualEffectView(effect: UIBlurEffect(style: .light))
blurEffectView.frame = self.view.bounds
blurEffectView.autoresizingMask = [.flexibleWidth, .flexibleHeight]
view.addSubview(blurEffectView)
view.sendSubview(toBack: blurEffectView)
}
}
The TabBarController, which is the backgroundForegroundDelegate, will do the following to present that LockScreen:
lazy var lockScreenViewController = UIStoryboard(name: "Login", bundle: nil).instantiateViewController(withIdentifier: "LockScreenViewController")
func applicationDidEnterBackground() {
let visibleViewController = (self.selectedViewController as? UINavigationController)?.visibleViewController
(visibleViewController as? BackgroundForegroundDelegate)?.applicationDidEnterBackground()
lockScreenViewController.modalPresentationStyle = .overFullScreen
let window = UIApplication.shared.keyWindow!
if let modalVC = window.rootViewController?.presentedViewController {
// HERE it does crash
modalVC.present(lockScreenViewController, animated: false,
completion: nil)
} else {
window.rootViewController!.present(lockScreenViewController, animated: false, completion: nil)
}
}
I marked the line where the crashs occured.
We couldn't reproduce it on the same phone with the same OS.
What can go wrong here and how can we make it "safe"?
Crash Report:
Hardware Model: iPhone8,1
Process: MyApp [13594]
Path: /private/var/containers/Bundle/Application/**/MyApp.app/MyApp
Identifier: *hidden*
Version: 1565 (1.2.0)
Code Type: ARM-64 (Native)
Role: Foreground
Parent Process: launchd [1]
Coalition: *hidden*
Date/Time: 2017-09-24 14:46:10.5972 +0200
Launch Time: 2017-09-24 14:43:55.8968 +0200
OS Version: iPhone OS 11.0 (15A372)
Baseband Version: 4.00.01
Report Version: 104
Exception Type: EXC_CRASH (SIGABRT)
Exception Codes: 0x0000000000000000, 0x0000000000000000
Exception Note: EXC_CORPSE_NOTIFY
Triggered by Thread: 0
Last Exception Backtrace:
0 CoreFoundation 0x18261fd38 __exceptionPreprocess + 124 (NSException.m:166)
1 libobjc.A.dylib 0x181b34528 objc_exception_throw + 56 (objc-exception.mm:521)
2 UIKit 0x18bda189c -[UIViewController _presentViewController:withAnimationController:completion:] + 4828 (UIViewController.m:6945)
3 UIKit 0x18bda4074 __63-[UIViewController _presentViewController:animated:completion:]_block_invoke_2 + 68 (UIViewController.m:7453)
4 UIKit 0x18ba3ca84 +[UIView(Animation) performWithoutAnimation:] + 104 (UIView.m:11718)
5 UIKit 0x18bda3fc8 __63-[UIViewController _presentViewController:animated:completion:]_block_invoke + 220 (UIViewController.m:7451)
6 UIKit 0x18bda4488 -[UIViewController _performCoordinatedPresentOrDismiss:animated:] + 528 (UIViewController.m:7531)
7 UIKit 0x18bda3ea4 -[UIViewController _presentViewController:animated:completion:] + 188 (UIViewController.m:7462)
8 UIKit 0x18bb0e55c -[UIViewController presentViewController:animated:completion:] + 160 (UIViewController.m:7475)
9 MyApp 0x1041794cc _T013MyApp24TabBarControllerC29applicationDidEnterBackgroundyyF + 472 (TabBarController.swift:81)
10 MyApp 0x10417ace8 _T013MyApp24TabBarControllerCAA28BackgroundForegroundDelegateA2aDP019applicationDidEnterG0yyFTW + 20 (TabBarController.swift:0)
11 MyApp 0x104151aa0 _T013MyApp11AppDelegateC29applicationDidEnterBackgroundySo13UIApplicationCFTo + 192 (AppDelegate.swift:76)
12 UIKit 0x18bc9b648 __47-[UIApplication _applicationDidEnterBackground]_block_invoke + 180 (UIApplication.m:6096)
13 UIKit 0x18bd9e338 +[UIViewController _performWithoutDeferringTransitions:] + 128 (UIViewController.m:6538)
14 UIKit 0x18bc9b538 -[UIApplication _applicationDidEnterBackground] + 104 (UIApplication.m:6088)
15 UIKit 0x18bf2531c -[__UICanvasLifecycleMonitor_Compatability deactivateEventsOnly:withContext:forceExit:completion:] + 860 (_UICanvasLifecycleMonitor.m:375)
16 UIKit 0x18c68d760 __82-[_UIApplicationCanvas _transitionLifecycleStateWithTransitionContext:completion:]_block_invoke + 380 (_UIApplicationCanvas.m:0)
17 UIKit 0x18c68d58c -[_UIApplicationCanvas _transitionLifecycleStateWithTransitionContext:completion:] + 448 (_UIApplicationCanvas.m:156)
18 UIKit 0x18c4099c0 __125-[_UICanvasLifecycleSettingsDiffAction performActionsForCanvas:withUpdatedScene:settingsDiff:fromSettings:transitionContext:]_block_invoke + 220 (_UICanvasLifecycleSettingsDiffAction.m:210)
19 UIKit 0x18c59efc8 _performActionsWithDelayForTransitionContext + 112 (_UICanvasSettingsDiffAction.m:34)
20 UIKit 0x18c409870 -[_UICanvasLifecycleSettingsDiffAction performActionsForCanvas:withUpdatedScene:settingsDiff:fromSettings:transitionContext:] + 252 (_UICanvasLifecycleSettingsDiffAction.m:181)
21 UIKit 0x18c1f3850 -[_UICanvas scene:didUpdateWithDiff:transitionContext:completion:] + 364 (_UICanvas.m:517)
22 UIKit 0x18c098bd8 -[UIApplicationSceneClientAgent scene:handleEvent:withCompletion:] + 468 (UIApplicationSceneClientAgent.m:77)
23 FrontBoardServices 0x184cc221c __80-[FBSSceneImpl updater:didUpdateSettings:withDiff:transitionContext:completion:]_block_invoke.362 + 212 (FBSSceneImpl.m:571)
24 libdispatch.dylib 0x181fa5048 _dispatch_client_callout + 16 (object.m:502)
25 libdispatch.dylib 0x181fac6c8 _dispatch_block_invoke_direct$VARIANT$mp + 288 (queue.c:3025)
26 FrontBoardServices 0x184cf5a04 __FBSSERIALQUEUE_IS_CALLING_OUT_TO_A_BLOCK__ + 36 (FBSSerialQueue.m:164)
27 FrontBoardServices 0x184cf56a8 -[FBSSerialQueue _performNext] + 404 (FBSSerialQueue.m:196)
28 FrontBoardServices 0x184cf5c44 -[FBSSerialQueue _performNextFromRunLoopSource] + 56 (FBSSerialQueue.m:232)
29 CoreFoundation 0x1825c8358 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ + 24 (CFRunLoop.c:1982)
30 CoreFoundation 0x1825c82d8 __CFRunLoopDoSource0 + 88 (CFRunLoop.c:2017)
31 CoreFoundation 0x1825c7b60 __CFRunLoopDoSources0 + 204 (CFRunLoop.c:2053)
32 CoreFoundation 0x1825c5738 __CFRunLoopRun + 1048 (CFRunLoop.c:2920)
33 CoreFoundation 0x1824e62d8 CFRunLoopRunSpecific + 436 (CFRunLoop.c:3245)
34 GraphicsServices 0x184377f84 GSEventRunModal + 100 (GSEvent.c:2245)
35 UIKit 0x18ba92880 UIApplicationMain + 208 (UIApplication.m:3948)
36 MyApp 0x1040c100c main + 56 (ContactsService.swift:16)
37 libdyld.dylib 0x18200a56c start + 4
Thread 0 name:
Thread 0 Crashed:
0 libsystem_kernel.dylib 0x0000000182139348 __pthread_kill + 8
1 libsystem_pthread.dylib 0x000000018224d354 pthread_kill$VARIANT$mp + 396 (pthread.c:1484)
2 libsystem_c.dylib 0x00000001820a8fd8 abort + 140 (abort.c:91)
3 libc++abi.dylib 0x0000000181b0c068 abort_message + 132 (abort_message.cpp:75)
4 libc++abi.dylib 0x0000000181b0c210 default_terminate_handler() + 304 (cxa_default_handlers.cpp:68)
5 libobjc.A.dylib 0x0000000181b34810 _objc_terminate() + 124 (objc-exception.mm:657)
6 libc++abi.dylib 0x0000000181b2454c std::__terminate(void (*)()) + 16 (cxa_handlers.cpp:66)
7 libc++abi.dylib 0x0000000181b245b8 std::terminate() + 60 (cxa_handlers.cpp:97)
8 libdispatch.dylib 0x0000000181fa505c _dispatch_client_callout + 36 (object.m:505)
9 libdispatch.dylib 0x0000000181fac6c8 _dispatch_block_invoke_direct$VARIANT$mp + 288 (queue.c:3025)
10 FrontBoardServices 0x0000000184cf5a04 __FBSSERIALQUEUE_IS_CALLING_OUT_TO_A_BLOCK__ + 36 (FBSSerialQueue.m:164)
11 FrontBoardServices 0x0000000184cf56a8 -[FBSSerialQueue _performNext] + 404 (FBSSerialQueue.m:196)
12 FrontBoardServices 0x0000000184cf5c44 -[FBSSerialQueue _performNextFromRunLoopSource] + 56 (FBSSerialQueue.m:232)
13 CoreFoundation 0x00000001825c8358 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ + 24 (CFRunLoop.c:1982)
14 CoreFoundation 0x00000001825c82d8 __CFRunLoopDoSource0 + 88 (CFRunLoop.c:2017)
15 CoreFoundation 0x00000001825c7b60 __CFRunLoopDoSources0 + 204 (CFRunLoop.c:2053)
16 CoreFoundation 0x00000001825c5738 __CFRunLoopRun + 1048 (CFRunLoop.c:2920)
17 CoreFoundation 0x00000001824e62d8 CFRunLoopRunSpecific + 436 (CFRunLoop.c:3245)
18 GraphicsServices 0x0000000184377f84 GSEventRunModal + 100 (GSEvent.c:2245)
19 UIKit 0x000000018ba92880 UIApplicationMain + 208 (UIApplication.m:3948)
20 MyApp 0x00000001040c100c main + 56 (ContactsService.swift:16)
21 libdyld.dylib 0x000000018200a56c start + 4
Thread 1 name:
Thread 1:
0 libsystem_kernel.dylib 0x0000000182118bc4 mach_msg_trap + 8
1 libsystem_kernel.dylib 0x0000000182118a3c mach_msg + 72 (mach_msg.c:103)
2 CoreFoundation 0x00000001825c7ce4 __CFRunLoopServiceMachPort + 196 (CFRunLoop.c:2613)
3 CoreFoundation 0x00000001825c58b0 __CFRunLoopRun + 1424 (CFRunLoop.c:2969)
4 CoreFoundation 0x00000001824e62d8 CFRunLoopRunSpecific + 436 (CFRunLoop.c:3245)
5 Foundation 0x0000000182f0e6e4 -[NSRunLoop(NSRunLoop) runMode:beforeDate:] + 304 (NSRunLoop.m:367)
6 Foundation 0x0000000182f2dafc -[NSRunLoop(NSRunLoop) runUntilDate:] + 96 (NSRunLoop.m:411)
7 UIKit 0x000000018c5de02c -[UIEventFetcher threadMain] + 136 (UIEventFetcher.m:422)
8 Foundation 0x000000018300f860 __NSThread__start__ + 996 (NSThread.m:1181)
9 libsystem_pthread.dylib 0x000000018224c32c _pthread_body + 308 (pthread.c:740)
10 libsystem_pthread.dylib 0x000000018224c1f8 _pthread_start + 312 (pthread.c:799)
11 libsystem_pthread.dylib 0x000000018224ac38 thread_start + 4
Thread 2 name:
Thread 2:
0 libsystem_kernel.dylib 0x0000000182118bc4 mach_msg_trap + 8
1 libsystem_kernel.dylib 0x0000000182118a3c mach_msg + 72 (mach_msg.c:103)
2 CoreFoundation 0x00000001825c7ce4 __CFRunLoopServiceMachPort + 196 (CFRunLoop.c:2613)
3 CoreFoundation 0x00000001825c58b0 __CFRunLoopRun + 1424 (CFRunLoop.c:2969)
4 CoreFoundation 0x00000001824e62d8 CFRunLoopRunSpecific + 436 (CFRunLoop.c:3245)
5 Foundation 0x0000000182f0e6e4 -[NSRunLoop(NSRunLoop) runMode:beforeDate:] + 304 (NSRunLoop.m:367)
6 Foundation 0x0000000182f6062c -[NSRunLoop(NSRunLoop) run] + 88 (NSRunLoop.m:389)
7 MyApp 0x00000001041c7330 +[GAI threadMain:] + 64 (GAI.m:228)
8 Foundation 0x000000018300f860 __NSThread__start__ + 996 (NSThread.m:1181)
9 libsystem_pthread.dylib 0x000000018224c32c _pthread_body + 308 (pthread.c:740)
10 libsystem_pthread.dylib 0x000000018224c1f8 _pthread_start + 312 (pthread.c:799)
11 libsystem_pthread.dylib 0x000000018224ac38 thread_start + 4
Thread 3:
0 libsystem_kernel.dylib 0x0000000182139dbc __workq_kernreturn + 8
1 libsystem_pthread.dylib 0x000000018224afb0 _pthread_wqthread + 884 (pthread.c:0)
2 libsystem_pthread.dylib 0x000000018224ac30 start_wqthread + 4
Thread 4:
0 libsystem_pthread.dylib 0x000000018224ac2c start_wqthread + 0 (pthread.c:2447)
Thread 5:
0 libsystem_pthread.dylib 0x000000018224ac2c start_wqthread + 0 (pthread.c:2447)
Thread 6 name:
Thread 6:
0 libsystem_kernel.dylib 0x0000000182118bc4 mach_msg_trap + 8
1 libsystem_kernel.dylib 0x0000000182118a3c mach_msg + 72 (mach_msg.c:103)
2 libdispatch.dylib 0x0000000181fbacf4 _dispatch_mach_send_and_wait_for_reply + 644 (mach.c:831)
3 libdispatch.dylib 0x0000000181fbb19c dispatch_mach_send_with_result_and_wait_for_reply$VARIANT$mp + 56 (mach.c:1958)
4 libxpc.dylib 0x00000001822879cc xpc_connection_send_message_with_reply_sync + 196 (connection.c:802)
5 BaseBoard 0x0000000184aed634 -[BSXPCMessage sendSynchronouslyToConnection:error:] + 76 (BSXPCMessage.m:189)
6 BaseBoard 0x0000000184ae9dac -[BSBaseXPCClient _sendMessage:withReplyHandler:waitForReply:waitDuration:] + 320 (BSBaseXPCClient.m:233)
7 AssertionServices 0x0000000184b3cc10 -[BKSAssertionClientMultiplexer sendEvent:withAssertionType:forEventType:responseHandler:] + 272 (BKSAssertionClientMultiplexer.m:87)
8 AssertionServices 0x0000000184b36a98 -[BKSProcessAssertionClient sendCreateEvent:error:] + 116 (BKSProcessAssertionClient.m:53)
9 AssertionServices 0x0000000184b3a4c8 -[BKSAssertion _clientQueue_acquireAssertion] + 136 (BKSAssertion.m:293)
10 AssertionServices 0x0000000184b3a0fc __45-[BKSAssertion _registerAssertionAndAcquire:]_block_invoke + 80 (BKSAssertion.m:235)
11 libdispatch.dylib 0x0000000181fa5088 _dispatch_call_block_and_release + 24 (init.c:994)
12 libdispatch.dylib 0x0000000181fa5048 _dispatch_client_callout + 16 (object.m:502)
13 libdispatch.dylib 0x0000000181faee48 _dispatch_queue_serial_drain$VARIANT$mp + 528 (inline_internal.h:2500)
14 libdispatch.dylib 0x0000000181faf7d8 _dispatch_queue_invoke$VARIANT$mp + 340 (queue.c:5302)
15 libdispatch.dylib 0x0000000181fb0200 _dispatch_root_queue_drain_deferred_wlh$VARIANT$mp + 400 (queue.c:5920)
16 libdispatch.dylib 0x0000000181fb84a0 _dispatch_workloop_worker_thread$VARIANT$mp + 644 (source.c:2515)
17 libsystem_pthread.dylib 0x000000018224afe0 _pthread_wqthread + 932 (pthread.c:2207)
18 libsystem_pthread.dylib 0x000000018224ac30 start_wqthread + 4
Thread 7:
0 libsystem_pthread.dylib 0x000000018224ac2c start_wqthread + 0 (pthread.c:2447)
Thread 8 name:
Thread 8:
0 libsystem_kernel.dylib 0x0000000182118bc4 mach_msg_trap + 8
1 libsystem_kernel.dylib 0x0000000182118a3c mach_msg + 72 (mach_msg.c:103)
2 CoreFoundation 0x00000001825c7ce4 __CFRunLoopServiceMachPort + 196 (CFRunLoop.c:2613)
3 CoreFoundation 0x00000001825c58b0 __CFRunLoopRun + 1424 (CFRunLoop.c:2969)
4 CoreFoundation 0x00000001824e62d8 CFRunLoopRunSpecific + 436 (CFRunLoop.c:3245)
5 CFNetwork 0x0000000182c4fb40 +[NSURLConnection(Loader) _resourceLoadLoop:] + 404 (NSURLConnection.mm:367)
6 Foundation 0x000000018300f860 __NSThread__start__ + 996 (NSThread.m:1181)
7 libsystem_pthread.dylib 0x000000018224c32c _pthread_body + 308 (pthread.c:740)
8 libsystem_pthread.dylib 0x000000018224c1f8 _pthread_start + 312 (pthread.c:799)
9 libsystem_pthread.dylib 0x000000018224ac38 thread_start + 4
Thread 0 crashed with ARM Thread State (64-bit):
x0: 0x0000000000000000 x1: 0x0000000000000000 x2: 0x0000000000000000 x3: 0x00000001c42ea5b7
x4: 0x0000000181b29afd x5: 0x000000016bd425a0 x6: 0x000000000000006e x7: 0xffffffffffffffec
x8: 0x0000000008000000 x9: 0x0000000004000000 x10: 0x000000018225163c x11: 0x0000000000000003
x12: 0xffffffffffffffff x13: 0x0000000000000001 x14: 0x00000001820bf557 x15: 0x0000000000000010
x16: 0x0000000000000148 x17: 0x00000000ffffffff x18: 0x0000000000000000 x19: 0x0000000000000006
x20: 0x00000001b2fe3b80 x21: 0x000000016bd425a0 x22: 0x0000000000000303 x23: 0x00000001b2fe3c60
x24: 0x0000000000002403 x25: 0x0000000000002303 x26: 0x0000000000000001 x27: 0x0000000000000000
x28: 0x00000001c41fc808 fp: 0x000000016bd42500 lr: 0x000000018224d354
sp: 0x000000016bd424d0 pc: 0x0000000182139348 cpsr: 0x00000000

Answer 1

Every time I need to present multiple modals I end up using addChildViewController() to add the vc's.
The I'm animating the childViewController.view in from the bottom edge of the screen to immitate the systems modal presentation animation. 👍
If you want to use the systems present() method make sure you really present on the top most view controller.