当我的 UITextField 之一具有焦点并且一个离开应用程序时，当一个人返回应用程序时，它会可靠地崩溃并出现下面的堆栈跟踪。我不相信当应用程序重新进入前台时我有任何特定的代码可以运行。由于没有任何元素引用我的代码，我不知道如何处理这个错误。提前谢谢了！！！
山姆
#0 0x01e2c09b in objc_msgSend ()
#1 0x011e744d in -[CALayer actionForKey:] ()
#2 0x011e27bd in actionForKey(CALayer*, CA::Transaction*, NSString*) ()
#3 0x011e2735 in CA::Layer::begin_change(CA::Transaction*, unsigned int, objc_object*&) ()
#4 0x011e661f in CA::Layer::remove_sublayer(CA::Transaction*, CALayer*) ()
#5 0x011e6cd1 in CA::Layer::insert_sublayer(CA::Transaction*, CALayer*, unsigned long) ()
#6 0x011e7136 in -[CALayer addSublayer:] ()
#7 0x158fd468 in __49-[UIKeyboardSliceTransitionView initializeLayers]_block_invoke_0 ()
#8 0x02570e7c in __NSArrayEnumerate ()
#9 0x02570a16 in -[NSArray enumerateObjectsWithOptions:usingBlock:] ()
#10 0x02570925 in -[NSArray enumerateObjectsUsingBlock:] ()
#11 0x158fd160 in -[UIKeyboardSliceTransitionView initializeLayers] ()
#12 0x158fd0b3 in -[UIKeyboardSliceTransitionView initWithFrame:] ()
#13 0x158fcf36 in -[TIRivenFactory transitionView] ()
#14 0x01605810 in -[UIKeyboardLayoutStar refreshForRivenPreferences] ()
#15 0x01606280 in -[UIKeyboardLayoutStar setKeyboardName:appearance:] ()
#16 0x0160ac8b in -[UIKeyboardLayoutStar showKeyboardType:appearance:orientation:withShift:] ()
#17 0x014e7c2a in -[UIKeyboardImpl updateLayout] ()
#18 0x014e4a8f in -[UIKeyboardImpl setDelegate:force:] ()
#19 0x014e44ae in -[UIKeyboardImpl setDelegate:] ()
#20 0x017196d3 in -[UIKeyboardAutomatic willResume:] ()
#21 0x00cb74f9 in __57-[NSNotificationCenter addObserver:selector:name:object:]_block_invoke_0 ()
#22 0x025d10c5 in ___CFXNotificationPost_block_invoke_0 ()
#23 0x0252befa in _CFXNotificationPost ()
#24 0x00bebbb2 in -[NSNotificationCenter postNotificationName:object:userInfo:] ()
#25 0x013760ba in -[UIApplication _sendWillEnterForegroundCallbacks] ()
#26 0x01376588 in -[UIApplication _handleApplicationResumeEvent:] ()
#27 0x01376e74 in -[UIApplication handleEvent:withNewEvent:] ()
#28 0x01377beb in -[UIApplication sendEvent:] ()
#29 0x01369698 in _UIApplicationHandleEvent ()
#30 0x02097df9 in _PurpleEventCallback ()
#31 0x024faf3f in __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ ()
#32 0x024fa96f in __CFRunLoopDoSources0 ()
#33 0x0251d734 in __CFRunLoopRun ()
#34 0x0251cf44 in CFRunLoopRunSpecific ()
#35 0x0251ce1b in CFRunLoopRunInMode ()
#36 0x020967e3 in GSEventRunModal ()
#37 0x02096668 in GSEventRun ()
#38 0x01366ffc in UIApplicationMain ()
#39 0x000028ad in main at /Users/pg/code/PortBuilder/PortBuilder/main.m:9
#40 0x000027d5 in start ()