iOS 11. KVO_IS_RETAINING_ALL_OBSERVERS_OF_THIS_OBJECT_IF_IT_CRASHES_AN_OBSERVER_WAS_OVERRELEASED_OR_SMASHED是什么意思？

Question

在新的iOS11中,我得到了一些奇怪的例外.我不明白为什么会这样.在之前的iOS中,没有这样的例外.附加日志:

Crashed: com.apple.main-thread
0  libobjc.A.dylib                0x180a5e7e8 object_isClass + 16
1  Foundation                     0x181f013e8 KVO_IS_RETAINING_ALL_OBSERVERS_OF_THIS_OBJECT_IF_IT_CRASHES_AN_OBSERVER_WAS_OVERRELEASED_OR_SMASHED + 68
2  Foundation                     0x181eff8ec NSKeyValueWillChangeWithPerThreadPendingNotifications + 300
3  QuartzCore                     0x18555a6dc CAAnimation_setter(CAAnimation*, unsigned int, _CAValueType, void const*) + 156
4  QuartzCore                     0x18555d388 -[CAPropertyAnimation setKeyPath:] + 32
5  UIKit                          0x18a9b1a08 -[UIImageView startAnimating] + 876
6  UIKit                          0x18a9b0e78 -[UIActivityIndicatorView startAnimating] + 48
7  UIKit                          0x18a9b0174 -[UIActivityIndicatorView _didMoveFromWindow:toWindow:] + 212
8  UIKit                          0x18a95845c -[UIView(Internal) _didMoveFromWindow:toWindow:] + 712
9  UIKit                          0x18a95845c -[UIView(Internal) _didMoveFromWindow:toWindow:] + 712
10 UIKit                          0x18a95845c -[UIView(Internal) _didMoveFromWindow:toWindow:] + 712
11 UIKit                          0x18a95845c -[UIView(Internal) _didMoveFromWindow:toWindow:] + 712
12 UIKit                          0x18a95845c -[UIView(Internal) _didMoveFromWindow:toWindow:] + 712
13 UIKit                          0x18a95845c -[UIView(Internal) _didMoveFromWindow:toWindow:] + 712
14 UIKit                          0x18a95845c -[UIView(Internal) _didMoveFromWindow:toWindow:] + 712
15 UIKit                          0x18a95845c -[UIView(Internal) _didMoveFromWindow:toWindow:] + 712
16 UIKit                          0x18a957918 __45-[UIView(Hierarchy) _postMovedFromSuperview:]_block_invoke + 156
17 Foundation                     0x181e7c59c -[NSISEngine withBehaviors:performModifications:] + 168
18 UIKit                          0x18a95778c -[UIView(Hierarchy) _postMovedFromSuperview:] + 824
19 UIKit                          0x18a96339c -[UIView(Internal) _addSubview:positioned:relativeTo:] + 1728
20 UIKit                          0x18abb3158 __53-[_UINavigationParallaxTransition animateTransition:]_block_invoke_2 + 1660
21 UIKit                          0x18a969a84 +[UIView(Animation) performWithoutAnimation:] + 104
22 UIKit                          0x18ab23864 __53-[_UINavigationParallaxTransition animateTransition:]_block_invoke + 264
23 UIKit                          0x18ac418a4 +[UIView(Internal) _performBlockDelayingTriggeringResponderEvents:] + 220
24 UIKit                          0x18ab2321c -[_UINavigationParallaxTransition animateTransition:] + 1112
25 UIKit                          0x18aae1720 -[UINavigationController _startCustomTransition:] + 3444
26 UIKit                          0x18aa02e04 -[UINavigationController _startDeferredTransitionIfNeeded:] + 712
27 UIKit                          0x18aa02a34 -[UINavigationController __viewWillLayoutSubviews] + 124
28 UIKit                          0x18aa0295c -[UILayoutContainerView layoutSubviews] + 188
29 UIKit                          0x18a959000 -[UIView(CALayerDelegate) layoutSublayersOfLayer:] + 1256
30 QuartzCore                     0x1855290b4 -[CALayer layoutSublayers] + 184
31 QuartzCore                     0x18552d194 CA::Layer::layout_if_needed(CA::Transaction*) + 332
32 QuartzCore                     0x18549bf24 CA::Context::commit_transaction(CA::Transaction*) + 336
33 QuartzCore                     0x1854c2340 CA::Transaction::commit() + 540
34 QuartzCore                     0x1854c3180 CA::Transaction::observer_callback(__CFRunLoopObserver*, unsigned long, void*) + 92
35 CoreFoundation                 0x1814f38b8 __CFRUNLOOP_IS_CALLING_OUT_TO_AN_OBSERVER_CALLBACK_FUNCTION__ + 32
36 CoreFoundation                 0x1814f1270 __CFRunLoopDoObservers + 412
37 CoreFoundation                 0x1814f182c __CFRunLoopRun + 1292
38 CoreFoundation                 0x1814122d8 CFRunLoopRunSpecific + 436
39 GraphicsServices               0x1832a3f84 GSEventRunModal + 100
40 UIKit                          0x18a9bf880 UIApplicationMain + 208

曾经遇到过这个？它是什么以及如何打败它？

Answer 1

它与KVO = Key-Value Observing有关.检查您是否正在调用该功能

object.addObserver(self, forKeyPath:..., options:..., context:...)

某处; 那是你的KVO观察者.该类还将覆盖该函数

observeValue(forKeyPath:of:change:context:)

正如错误信息所示,如果你在这里遇到崩溃,那就意味着观察者被"过度释放"或"被粉碎".我认为这只是意味着它仍在观察关键路径时被释放.

怎么解决？

斯威夫特3

如果您需要在Swift 3中修复它(就像我一样),请确保在您removeObserver不再对观察关键路径感兴趣时调用.最简单的方法是向deinit观察者添加一个方法:

deinit {
    object.removeObserver(self, forKeyPath:#keyPath(same.as.in.addObserver))
}

确保object使用您使用的相同引用替换和键路径addObserver!

更多信息:https://cocoacasts.com/key-value-observing-kvo-and-swift-3/

Swift 4/iOS

从Swift 4/iOS 11中你可以使用块,就像这个问题一样:在Swift 4中,如何删除基于块的KVO观察者？

您可以像这样添加观察者,而不是使用observeValue方法:

var observer: NSKeyValueObservation? = foo.observe(.value, options: [.new]) { (foo, change) in
   print(change.newValue)     // whatever needs to happen when the value changes
}

在iOS中,您仍应保留对观察者的引用并invalidate在适当的时间(例如在其中deinit或在其中)对其进行调用viewWillDisappear.

Swift 4/macOS

如果您正在为macOS 10.13或更高版本开发,在某些情况下它们不再需要被删除.从文档引用:

轻松的键值观察注销要求

在10.13之前,如果在autonotifying对象的-dealloc完成运行后仍然注册了任何观察者,KVO将抛出异常.另外,如果所有观察者都被删除了,但是在dealloc期间一些观察者被从另一个线程中删除了,那么异常将被错误地抛出.该要求已在10.13中放宽,但有两个条件:

• 该对象必须使用KVO自动调整,而不是手动调用-will和-didChangeValueForKey :(即它不应该从+自动返回NONotifiesObserversForKey :)
• 对象不得覆盖内部KVO状态的(私有)访问器

如果所有这些都是真的,那么-dealloc返回后的任何剩余观察者将被KVO清理; 这比重复调用-removeObserver方法更有效.

资料来源:https://developer.apple.com/library/archive/releasenotes/Foundation/RN-Foundation/index.html