Enumeration Mutation During UIView transitionWithView - iphone

Question

I'm experience an occasional crash of my iPhone application where I'm getting the following exception
NSGenericException', reason: '*** Collection <CALayerArray: 0x26f6b0> was mutated while being enumerated.
With the stack trace on the crashing thread of
Thread 0 Crashed:
0 libSystem.B.dylib 0x00078ac8 __kill + 8
1 libSystem.B.dylib 0x00078ab8 kill + 4
2 libSystem.B.dylib 0x00078aaa raise + 10
3 libSystem.B.dylib 0x0008d03a abort + 50
4 libstdc++.6.dylib 0x00044a20 __gnu_cxx::__verbose_terminate_handler() + 376
5 libobjc.A.dylib 0x00005958 _objc_terminate + 104
6 libstdc++.6.dylib 0x00042df2 __cxxabiv1::__terminate(void (*)()) + 46
7 libstdc++.6.dylib 0x00042e46 std::terminate() + 10
8 libstdc++.6.dylib 0x00042f16 __cxa_throw + 78
9 libobjc.A.dylib 0x00004838 objc_exception_throw + 64
10 CoreFoundation 0x0009f850 __NSFastEnumerationMutationHandler + 208
11 libobjc.A.dylib 0x0000a51a objc_enumerationMutation + 18
12 UIKit 0x00007bfe -[UIView(Hierarchy) _makeSubtreePerformSelector:withObject:withObject:copySublayers:] + 142
13 UIKit 0x00007c2e -[UIView(Hierarchy) _makeSubtreePerformSelector:withObject:withObject:copySublayers:] + 190
14 UIKit 0x00007cd2 -[UIView(Hierarchy) _makeSubtreePerformSelector:withObject:] + 22
15 UIKit 0x00007628 -[UIView(Internal) _addSubview:positioned:relativeTo:] + 304
16 UIKit 0x000074e8 -[UIView(Hierarchy) addSubview:] + 16
17 UIKit 0x0006c350 +[UIViewControllerWrapperView wrapperViewForView:frame:] + 232
18 UIKit 0x00077d0c -[UINavigationController _startTransition:fromViewController:toViewController:] + 468
19 UIKit 0x00077abc -[UINavigationController _startDeferredTransitionIfNeeded] + 176
20 UIKit 0x00077a00 -[UINavigationController viewWillLayoutSubviews] + 8
21 UIKit 0x0006dca8 -[UILayoutContainerView layoutSubviews] + 132
22 UIKit 0x0000fbc0 -[UIView(CALayerDelegate) _layoutSublayersOfLayer:] + 20
23 CoreFoundation 0x0003e2e4 -[NSObject(NSObject) performSelector:withObject:] + 16
24 QuartzCore 0x0000f942 -[CALayer layoutSublayers] + 114
25 QuartzCore 0x0000f6fa CALayerLayoutIfNeeded + 178
26 QuartzCore 0x000094c4 CA::Context::commit_transaction(CA::Transaction*) + 204
27 QuartzCore 0x000092da CA::Transaction::commit() + 186
28 QuartzCore 0x0002d9b6 CA::Transaction::observer_callback(__CFRunLoopObserver*, unsigned long, void*) + 46
29 CoreFoundation 0x00030236 __CFRUNLOOP_IS_CALLING_OUT_TO_AN_OBSERVER_CALLBACK_FUNCTION__ + 10
30 CoreFoundation 0x000300aa __CFRunLoopDoObservers + 406
31 CoreFoundation 0x000276b4 __CFRunLoopRun + 848
32 CoreFoundation 0x00027270 CFRunLoopRunSpecific + 224
33 CoreFoundation 0x00027178 CFRunLoopRunInMode + 52
34 GraphicsServices 0x000045ec GSEventRunModal + 108
35 GraphicsServices 0x00004698 GSEventRun + 56
36 UIKit 0x0000411c -[UIApplication _run] + 396
37 UIKit 0x00002128 UIApplicationMain + 664
38 iDriveGreen 0x00003026 main (main.m:13)
39 iDriveGreen 0x00002ff0 start + 32
This crash is being triggered after the following code is executed.
StopRouteViewController *stopVC = [[StopRouteViewController alloc] init];
[UIView transitionWithView:self.navigationController.view
duration:0.5
options:UIViewAnimationOptionTransitionFlipFromLeft
animations:^{
[self.navigationController pushViewController:stopVC animated:NO];
}
completion:NULL];
[stopVC release];
Does this look blatantly wrong to anyone? My current thought is that is is either tied to stopVC being released before it is pushed or with transitioning with navigationController.view while at the same time pushing a new viewController to the navigationController.
Since this only occurs occasionally, I'd like to have a little more confidence before I commit a potential fix.

Answer 1

Yes, this is incorrect usage of the API. -[UINavigationController pushViewController:animated:] handles animation on its own. Even if you pass NO as the second argument, it is still manipulating the view hierarchy, which is what's causing your crash.
Basically, there is no reason to put a call to -[UINavigationController pushViewController:animated:] in an animation block, as you have done. If you want to animate the push of your controller, pass YES as the second argument.