ios - 获取 NSGenericException 原因为 : '*** Collection was mutated while being enumerated.'

Question

我得到这个 NSGenericException 原因是 Collection <NSConcreteHashTable: 0x282c34140> was mutated while being enumerated 即使我实际上并没有在我的代码中使用快速枚举。

当 NSFetchedResultsController 委托(delegate)作为我的核心数据对象中的一个属性被调用时，会触发此崩溃，最终调用此方法:

- (void)mutateCoordinatesOfClashingAnnotations:(NSArray *)annotations {

    NSDictionary *coordinateValuesToAnnotations = [self groupAnnotationsByLocationValue:annotations]; // returns a dictionary with key: coordinate (saved as NSValue) -> NSMutableArray of MKAnnotation objects

    for (int i=0; i<coordinateValuesToAnnotations.allKeys.count; i++) {
        NSValue *coordinateValue = coordinateValuesToAnnotations.allKeys[i];
        NSMutableArray *outletsAtLocation = coordinateValuesToAnnotations[coordinateValue];

        [self repositionAnnotations:outletsAtLocation];
    }
}

- (void)repositionAnnotations:(NSMutableArray *)annotations {

    for (int i = 0; i < annotations.count; i++) {

        double heading = radiansBetweenAnnotations * i;
        CLLocationCoordinate2D newCoordinate = [self calculateNewCoordinate];

        id <MKAnnotation> annotation = annotations[i];
        annotation.coordinate = newCoordinate; // this is where it crashes
    }
}

基本上，我正在尝试更改 MKAnnotation 对象(实际上也是一个 CoreData NSManagedObject)的“坐标”值，最终导致崩溃。奇怪的是，我得到了 'collection was mutated while being enumerated' 错误，即使上面的代码中没有任何“快速枚举”。我的意思是，我正在更改可变数组中对象的一个​​属性，该数组本身就是字典的一部分。

不幸的是，由于“注释”是一个 NSManagedObject，我不能只是从数组中“复制”它，然后更改复制的值并替换数组中的对象。

崩溃报告如下所示:

*** Terminating app due to uncaught exception 'NSGenericException', reason: '*** Collection <NSConcreteHashTable: 0x282c34140> was mutated while being enumerated.'

Last Exception Backtrace:
0   CoreFoundation                       0x00000001c058696c __exceptionPreprocess + 224
1   libobjc.A.dylib                      0x00000001c029f028 objc_exception_throw + 56
2   CoreFoundation                       0x00000001c05862d4 __NSFastEnumerationMutationHandler + 120
3   libobjc.A.dylib                      0x00000001c02b21a4 objc_enumerationMutation + 28
4   Foundation                           0x00000001c08706a8 -[NSConcreteHashTable countByEnumeratingWithState:objects:count:] + 72
5   MapKit                               0x00000001ce114b64 -[MKAnnotationManager observeValueForKeyPath:ofObject:change:context:] + 804
6   Foundation                           0x00000001c093bf14 NSKeyValueNotifyObserver + 288
7   Foundation                           0x00000001c093e01c NSKeyValueDidChange + 332
8   Foundation                           0x00000001c093b740 NSKeyValueDidChangeWithPerThreadPendingNotifications + 148
9   CoreData                             0x00000001c5006e38 _PF_ManagedObject_DidChangeValueForKey + 76
10  Foundation                           0x00000001c093784c NSKVOForwardInvocation + 336
11  CoreFoundation                       0x00000001c058adc0 ___forwarding___ + 676
12  CoreFoundation                       0x00000001c058d3a0 _CF_forwarding_prep_0 + 92
13  CJournal                             0x00000001049fc930 -[MapViewShared repositionAnnotations:] (MapViewShared.m:656)
14  CJournal                             0x00000001049fc580 -[MapViewShared mutateCoordinatesOfClashingAnnotations:] (MapViewShared.m:616)
15  CJournal                             0x0000000104a1fa98 -[MapViewController controllerDidChangeContent:] (MapViewController.m:1104)
16  CoreData                             0x00000001c50572a4 __82-[NSFetchedResultsController(PrivateMethods) _core_managedObjectContextDidChange:]_block_invoke + 5868
17  CoreData                             0x00000001c5015aac developerSubmittedBlockToNSManagedObjectContextPerform + 160
18  CoreData                             0x00000001c4ee01c4 -[NSManagedObjectContext performBlockAndWait:] + 208
19  CoreData                             0x00000001c4ee981c -[NSFetchedResultsController(PrivateMethods) _core_managedObjectContextDidChange:] + 120
20  Foundation                           0x00000001c095106c __57-[NSNotificationCenter addObserver:selector:name:object:]_block_invoke_2 + 24
21  CoreFoundation                       0x00000001c04de99c __CFNOTIFICATIONCENTER_IS_CALLING_OUT_TO_AN_OBSERVER__ + 24
22  CoreFoundation                       0x00000001c04de9ec ___CFXRegistrationPost1_block_invoke + 64
23  CoreFoundation                       0x00000001c04ddce4 _CFXRegistrationPost1 + 392
24  CoreFoundation                       0x00000001c04dd97c ___CFXNotificationPost_block_invoke + 104
25  CoreFoundation                       0x00000001c0456910 -[_CFXNotificationRegistrar find:object:observer:enumerator:] + 1420
26  CoreFoundation                       0x00000001c04dd2ac _CFXNotificationPost + 1264
27  Foundation                           0x00000001c083fbfc -[NSNotificationCenter postNotificationName:object:userInfo:] + 60
28  CoreData                             0x00000001c4eed264 -[NSManagedObjectContext(_NSInternalNotificationHandling) _postObjectsDidChangeNotificationWithUserInfo:] + 512
29  CoreData                             0x00000001c4ee95fc -[NSManagedObjectContext(_NSInternalChangeProcessing) _createAndPostChangeNotification:deletions:updates:refreshes:deferrals:wasMerge:] + 1244
30  CoreData                             0x00000001c4ee886c -[NSManagedObjectContext(_NSInternalChangeProcessing) _processRecentChanges:] + 980
31  CoreData                             0x00000001c501b48c _performRunLoopAction + 376
32  CoreFoundation                       0x00000001c0501524 __CFRUNLOOP_IS_CALLING_OUT_TO_AN_OBSERVER_CALLBACK_FUNCTION__ + 32
33  CoreFoundation                       0x00000001c04fc1c4 __CFRunLoopDoObservers + 416
34  CoreFoundation                       0x00000001c04fc774 __CFRunLoopRun + 1288
35  CoreFoundation                       0x00000001c04fbf40 CFRunLoopRunSpecific + 476
36  GraphicsServices                     0x00000001ca779534 GSEventRunModal + 104
37  UIKitCore                            0x00000001c4674a60 UIApplicationMain + 1936
38  CJournal                             0x00000001048d8c44 main (main.m:20)
39  libdyld.dylib                        0x00000001c037ae18 start + 0

有人可以帮我在这里找到问题吗？我使用的是什么我看不到的“枚举”？还是有其他事情发生？

Answer 1

当您更改坐标时，它看起来像 MKAnnotationManager观察变化，然后通过枚举计算其哈希表，也许您已经在枚举注释。
在任何情况下，您都不应该将模型对象添加到 View 中，这会破坏 MVC。 Controller 的工作是通过注释对象获取模型并将其格式化为 View 。一种方法是创建 MKPointAnnotation来自您的fetchedObjects (或创建一个 MKPointAnnotation 子类并使用您的模型对象将其存储在弱属性中进行初始化)并将它们添加到 map 中。在 FRC 的 didChangeObject您可以从模型对象更新注释。 map 的注释 View 正在对注释的坐标进行 KVO，因此它会自动更新其在 map 上的位置。在您的模型对象上创建一个类别(参见 docs )以存储延迟加载的注释(使用 objc_setAssociatedObject )。