title: iOS 11. What the KVO_IS_RETAINING_ALL_OBSERVERS_OF_THIS_OBJECT_IF_IT_CRASHES_AN_OBSERVER_WAS_OVERRELEASED_OR_SMASHED is mean?
body: <p>In the new iOS11, I get some strange exceptions. I do not understand why this is happening. In the previous iOS, there was no such exception. Log attached:</p>
  
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
  <div class="snippet-code">
  <pre class="snippet-code-html lang-html prettyprint-override"><code>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</code></pre>
  </div>
  </div>
  </p>
  
  <p>Who ever encountered this? What is it and how to defeat it?</p>