ios - 什么样的事情会导致 viewWillLayoutSubviews 在后台线程中运行？

Question

我在我的应用程序中检测到罕见的崩溃。堆栈跟踪没有帮助。它与我的代码没有直接关系:

*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[NSAttributeDictionary textContainerForAttributedString:containerSize:lineFragmentPadding:]: unrecognized selector sent to instance 0x1b8d89c0'

Last Exception Backtrace:
0   CoreFoundation                      0x2e23bfd3 __exceptionPreprocess + 131
1   libobjc.A.dylib                     0x38ab2ccf objc_exception_throw + 38
2   CoreFoundation                      0x2e23f967 -[NSObject(NSObject) doesNotRecognizeSelector:] + 202
3   CoreFoundation                      0x2e23e253 ___forwarding___ + 706
4   CoreFoundation                      0x2e18d7f8 __forwarding_prep_0___ + 24
5   UIFoundation                        0x35e77a25 __NSStringDrawingEngine + 12204
6   UIFoundation                        0x35e749a7 -[NSString(NSExtendedStringDrawing) drawWithRect:options:attributes:context:] + 150
7   UIKit                               0x30a70d21 -[UILabel _drawTextInRect:baselineCalculationOnly:] + 4224
8   UIKit                               0x30ad7009 -[UILabel drawTextInRect:] + 500
9   UIKit                               0x30ad6e0b -[UILabel drawRect:] + 78
10  UIKit                               0x30ad6da5 -[UIView(CALayerDelegate) drawLayer:inContext:] + 372
11  QuartzCore                          0x307042c1 -[CALayer drawInContext:] + 100
12  QuartzCore                          0x306ede3f CABackingStoreUpdate_ + 1854
13  QuartzCore                          0x307c8d6d ___ZN2CA5Layer8display_Ev_block_invoke + 52
14  QuartzCore                          0x306ed6f3 x_blame_allocations + 82
15  QuartzCore                          0x306ed39b CA::Layer::display_() + 1106
16  QuartzCore                          0x306d103d CA::Layer::display_if_needed(CA::Transaction*) + 208
17  QuartzCore                          0x306d0cd5 CA::Layer::layout_and_display_if_needed(CA::Transaction*) + 24
18  QuartzCore                          0x306d06df CA::Context::commit_transaction(CA::Transaction*) + 230
19  QuartzCore                          0x306d04ef CA::Transaction::commit() + 314
20  QuartzCore                          0x306fda83 CA::Transaction::release_thread(void*) + 162
21  libsystem_pthread.dylib             0x390dd68d _pthread_tsd_cleanup + 164
22  libsystem_pthread.dylib             0x390dd40b _pthread_exit + 86
23  libsystem_pthread.dylib             0x390de17d pthread_exit + 28
24  Foundation                          0x2eb7846f +[NSThread exit] + 10
25  Foundation                          0x2ec24a7d __NSThread__main__ + 1092
26  libsystem_pthread.dylib             0x390de919 _pthread_body + 140
27  libsystem_pthread.dylib             0x390de88b _pthread_start + 102
28  libsystem_pthread.dylib             0x390dcaa4 thread_start + 8

因此，我尝试添加更多调试信息以了解有关崩溃的更多信息。我可以找到 viewWillLayoutSubviews 的踪迹。它在后台被调用。如果我检测到它在后台，我可以退出该功能。但这是一个肮脏的黑客。我想通过阻止“things”在后台线程中调用应用程序 viewWillLayoutSubviews 来正确修复它。

我还没有找到那些“东西”，因为堆栈跟踪没有帮助。

frame #1: 0x32946d16 UIKit`-[UIView(CALayerDelegate) layoutSublayersOfLayer:] + 314
frame #2: 0x325c462a QuartzCore`-[CALayer layoutSublayers] + 142
frame #3: 0x325bfe3a QuartzCore`CA::Layer::layout_if_needed(CA::Transaction*) + 350
frame #4: 0x325bfccc QuartzCore`CA::Layer::layout_and_display_if_needed(CA::Transaction*) + 16
frame #5: 0x325bf6de QuartzCore`CA::Context::commit_transaction(CA::Transaction*) + 230
frame #6: 0x325bf4ee QuartzCore`CA::Transaction::commit() + 314
frame #7: 0x325eca82 QuartzCore`CA::Transaction::release_thread(void*) + 162
frame #8: 0x3af0568c libsystem_pthread.dylib`_pthread_tsd_cleanup + 164
frame #9: 0x3af0540a libsystem_pthread.dylib`_pthread_exit + 86
frame #10: 0x3af0617c libsystem_pthread.dylib`pthread_exit + 28
frame #11: 0x30a6746e Foundation`+[NSThread exit] + 10
frame #12: 0x30b13a7c Foundation`__NSThread__main__ + 1092
frame #13: 0x3af06918 libsystem_pthread.dylib`_pthread_body + 140
frame #14: 0x3af0688a libsystem_pthread.dylib`_pthread_start + 102`

那些“东西”可以是什么？

Answer 1

当你在后台调用一些必须在主线程上运行的东西时，就会发生这种崩溃。

找到确切的线路几乎是不可能的。我发现结果中有很多 NSLog 行和 [NSThread isMainThread] 行。

调用 UI 元素上的几乎所有内容(尤其是那些需要计算/更改大小的元素，触发 viewWillLayoutSubviews。在我的例子中，它是 UIImageViews 和 UILabels。

如果您找不到在后台进行 UI 更新的位置，请检查您是否在后台发布了 NSNotification。