iphone - 错误 '*** Collection <__NSCFDictionary: 0x563560> was mutated while being enumerated.'

Question

此代码导致错误，可能是什么问题？
我读过一些关于锁的东西，不可变对象(immutable对象)在多个线程上使用时很容易崩溃。但我真的不知道那是怎么回事......

-(void)cleanUpAllHexagons{

    //Cleaning up all hexagons from previous level
    NSLog(@"cleaning hexagons");
    NSString *spriteKey;
    NSString *touchAreaKey;

    NSMutableDictionary *existingHexagons = [[GameStateSingleton sharedMySingleton]getExistingHexagons];

        for (int i= 0; i < [existingHexagons count]; i++){
            spriteKey = [NSString stringWithFormat:@"hexagon%d",i];

            for (spriteKey in existingHexagons) {
                NSLog(@"the spritekey = %@",spriteKey);
                NSLog(@"%@", existingHexagons);
                NSLog(@"%@", [[existingHexagons valueForKey:spriteKey]objectForKey:@"realSprite"]);
                [self removeChild:[[existingHexagons valueForKey:spriteKey]objectForKey:@"realSprite"] cleanup:YES];
                [existingHexagons removeObjectForKey:spriteKey];
            } 


            hexTouchAreas = [[GameStateSingleton sharedMySingleton]getSharedHexTouchAreas];

            touchAreaKey = [NSString stringWithFormat:@"hexTouchArea%d",i];

            for (touchAreaKey in hexTouchAreas) {
                NSLog(@"the touchAreakey = %@",touchAreaKey);
                NSLog(@"%@", [hexTouchAreas valueForKey:touchAreaKey]);
                [self removeChild: [hexTouchAreas valueForKey:touchAreaKey] cleanup:YES];
            } 

        }  


}

Answer 1

要枚举这种情况下的所有键，您可以使用

for (spriteKey in [existingHexagons allKeys])

因此，您可以在枚举时修改字典。但是，如果您要删除所有键，您不应该在循环后使用 removeAllObjects 清空字典吗？代替方法？