即使在锁定后线程崩溃了 <__NSArrayM: 0x7f881a6b1900> 在枚举时发生了变异？

Question

这是我的代码，我正在根据我的条件删除多个值

-(void)collectionView:(UICollectionView *)collectionView didSelectItemAtIndexPath:(NSIndexPath *)indexPath
{
    PhotoCan *cell=[collectionView cellForItemAtIndexPath:indexPath];
    UIImage *getimg=[dicPhotoStore objectForKey:@(indexPath.row)];
    BOOL integer=[dic objectForKey:@(indexPath.row)];
    if(integer)
    {

        for(id img in arrFinalStore)
        {
            if(img==getimg)
            {


                NSLock *arrayLock = [[NSLock alloc] init];
                [arrayLock lock];
                    [arrFinalStore removeObject:img];
                NSLog(@"crash inside");
                [arrayLock unlock];

            }

        }
        @synchronized(self)
        {
            [dic removeObjectForKey:@(indexPath.row)];
            [dicPhotoStore removeObjectForKey:@(indexPath.row)];
        }
        NSLog(@"crashoutside");
        NSLog(@"inside false");
    }
    else
    {
        [dicPhotoStore setObject:cell.imgView.image forKey:@(indexPath.row)];
        [arrFinalStore addObject:cell.imgView.image];
        [dic setObject:@"1" forKey:@(indexPath.row)];
    }
    [_collection reloadData];
}

我了解到在尝试找出这个错误时出了点问题，请帮助我解决这个问题。

这是错误：

*** Terminating app due to uncaught exception 'NSGenericException', reason: '*** Collection <__NSArrayM: 0x7f881a6b1900> was mutated while being enumerated.'
*** First throw call stack:
(
    0   CoreFoundation                      0x000000010299fe65 __exceptionPreprocess + 165
    1   libobjc.A.dylib                     0x0000000102418deb objc_exception_throw + 48
    2   CoreFoundation                      0x000000010299f7c4 __NSFastEnumerationMutationHandler + 132
    3   PhotoCollageCanvas                  0x000000010056878f -[photoAssets collectionView:didSelectItemAtIndexPath:] + 767
    4   UIKit                               0x0000000103afb4a7 -[UICollectionView _selectItemAtIndexPath:animated:scrollPosition:notifyDelegate:] + 701
    5   UIKit                               0x0000000103b1d049 -[UICollectionView touchesEnded:withEvent:] + 574
    6   UIKit                               0x00000001034b6ef7 forwardTouchMethod + 349
    7   UIKit                               0x00000001034b6fc0 -[UIResponder touchesEnded:withEvent:] + 49
    8   UIKit                               0x00000001034b6ef7 forwardTouchMethod + 349
    9   UIKit                               0x00000001034b6fc0 -[UIResponder touchesEnded:withEvent:] + 49
    10  UIKit                               0x0000000103783ede _UIGestureRecognizerUpdate + 10279
    11  UIKit                               0x0000000103319f8a -[UIWindow _sendGesturesForEvent:] + 1137
    12  UIKit                               0x000000010331b1c0 -[UIWindow sendEvent:] + 849
    13  UIKit                               0x00000001032c9b66 -[UIApplication sendEvent:] + 263
    14  UIKit                               0x00000001032a3d97 _UIApplicationHandleEventQueue + 6844
    15  CoreFoundation                      0x00000001028cba31 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ + 17
    16  CoreFoundation                      0x00000001028c195c __CFRunLoopDoSources0 + 556
    17  CoreFoundation                      0x00000001028c0e13 __CFRunLoopRun + 867
    18  CoreFoundation                      0x00000001028c0828 CFRunLoopRunSpecific + 488
    19  GraphicsServices                    0x00000001058d8ad2 GSEventRunModal + 161
    20  UIKit                               0x00000001032a9610 UIApplicationMain + 171
    21  Photo                               0x0000000100566a5f main + 111
    22  libdyld.dylib                       0x000000010697b92d start + 1
    23  ???                                 0x0000000000000001 0x0 + 1
)

Answer 1

遍历数组时无法删除元素

            [arrFinalStore removeObject:img];

只需使用 [arrFinalStore removeObject:img];

Answer 2

你认为那把锁有什么用？它完全什么都不做。你创建了一个锁，锁定它，解锁它。由于该代码是唯一可以访问锁的代码，因此该锁不可能阻止任何人做任何事情。

而且它无论如何也解决不了你的问题。有人正在枚举那个数组。任何尝试修改它，正如您尝试的那样，当它被枚举时，都会崩溃。

您的代码是（删除了行）

    for(id img in arrFinalStore)
    {
        [arrFinalStore removeObject:img];
    }

该代码绝对会崩溃，没有什么可以阻止它崩溃。迭代时不能从数组中删除对象。

Answer 3

不是锁的问题。但问题是在迭代时您正在尝试删除元素，这意味着您进行并发修改会引发异常。

这是您可以使用的示例

for (item in originalArrayOfItems) {
if ([item shouldBeDiscarded])
    [discardedItems addObject:item];}

[originalArrayOfItems removeObjectsInArray:discardedItems];

Answer 4

遍历数组时无法删除元素，因此可以创建包含所有不需要对象的临时数组，然后调用 - (void)removeObjectsInArray:(NSArray<ObjectType> *)otherArray

所以你的代码是：

NSMutableArray *tempArray = [NSMutableArray array];
for(id img in arrFinalStore)
{
    if(img==getimg)
    {
        [tempArray addObject:img];
    }
}
[arrFinalStore removeObjectsInArray:tempArray];

您也可以使用简单的 for (int i = arrfinalstoer.count - 1; i > 0; --i) 进行枚举。

即使在锁定后线程崩溃了 <__NSArrayM: 0x7f881a6b1900> 在枚举时发生了变异？

Even though after lock the threads get crashed <__NSArrayM: 0x7f881a6b1900> was mutated while being enumerated?

objective-c

thread-safety

nsmutablearray

nslock

ios