NSFetchedResultsController在objectAtIndexPath上崩溃？

问题描述

尝试访问 NSFetchedResultsController 中的对象时，我遇到崩溃。

  2013-11-10 15：15：06.568 Social [11503：70b] CoreData：error：严重的应用程序错误。在核心数据更改处理期间捕获异常。这通常是NSManagedObjectContextObjectsDidChangeNotification的观察器中的错误。 ***  -  [__ NSArrayI objectAtIndex：]：索引2超出空数组的范围与userInfo（null）
 2013-11-10 15：15：06.570 Social [11503：70b] ***由于未捕获而终止应用程序exception'NSRangeException'，reason：'***  -  [__ NSArrayI objectAtIndex：]：index 2超出空数组的范围
  

viewDidLoad

   - （void）viewDidLoad 
 {
 [super viewDidLoad]; 
 
 self.resultController = [DataEngine sharedInstance] .postsFetchedResultController; 
 self.resultController.delegate = self; 
 [self.resultController performFetch：nil]; 
 
 [self.tableView reloadData]; 
 
 [[DataEngine sharedInstance] fetchInBackground]; 
} 
  

结果控制员委托
$ b

  #pragma mark  -  NSFetchedResultsControllerDelegate方法 -  
 
  - （void）controllerWillChangeContent：（NSFetchedResultsController *）controller 
 {
 [self.tableView beginUpdates]; 
} 
 
  - （void）controllerDidChangeContent：（NSFetchedResultsController *）controller 
 {
 [self.tableView endUpdates]; 
} 
 
  - （void）controller：（NSFetchedResultsController *）controller 
 didChangeObject：（id）anObject 
 atIndexPath：（NSIndexPath *）indexPath 
 forChangeType ：（NSFetchedResultsChangeType）type 
 newIndexPath：（NSIndexPath *）newIndexPath 
 {
 switch（type）
 {
 case NSFetchedResultsChangeInsert：
 [self.tableView insertRowsAtIndexPaths ：@ [indexPath] 
 withRowAnimation：UITableViewRowAnimationAutomatic]; 
 break; 
 
 case NSFetchedResultsChangeUpdate：
 [self.tableView reloadRowsAtIndexPaths：@ [indexPath] 
 withRowAnimation：UITableViewRowAnimationAutomatic]; 
 break; 
 
 case NSFetchedResultsChangeDelete：
 [self.tableView deleteRowsAtIndexPaths：@ [indexPath] 
 withRowAnimation：UITableViewRowAnimationAutomatic]; 
 break; 
 
 case NSFetchedResultsChangeMove：
 [self.tableView moveRowAtIndexPath：indexPath toIndexPath：newIndexPath]; 
 break; 
 
默认值：
 break; 
} 
} 
  

表视图 p>

  #pragma mark  -  UITableView Delegate& Dataset  -  
 
  - （NSInteger）tableView：（UITableView *）tableView numberOfRowsInSection：（NSInteger）section 
 {
 return self.resultController.fetchedObjects.count; 
} 
 
  - （UITableViewCell *）tableView：（UITableView *）tableView cellForRowAtIndexPath：（NSIndexPath *）indexPath 
 {
 return [self cellForRowAtIndexPath：indexPath]; 
} 
  

解决方案

在我的一个NSManagedObject子类我有下面的代码，导致的问题。 NSSets在NSManagedObejcts上自动初始化，不需要初始化它们。

   - （void）awakeFromFetch 
 {
 if（！self.comments）
 self.comments = [NSMutableSet set]; 
 
 if（！self.medias）
 self.medias = [NSMutableSet set];另一个问题是，在插入indexPath是null的时候，我不得不使用newIndexPath，而不是使用newIndexPath来代替。 
  case NSFetchedResultsChangeInsert：
 [self.tableView insertRowsAtIndexPaths：@ [newIndexPath] 
 withRowAnimation：UITableViewRowAnimationAutomatic]; 
 break; 
  
 
I'm getting a crash when trying to access an object in NSFetchedResultsController.
2013-11-10 15:15:06.568 Social[11503:70b] CoreData: error: Serious application error.  Exception was caught during Core Data change processing.  This is usually a bug within an observer of NSManagedObjectContextObjectsDidChangeNotification.  *** -[__NSArrayI objectAtIndex:]: index 2 beyond bounds for empty array with userInfo (null)
2013-11-10 15:15:06.570 Social[11503:70b] *** Terminating app due to uncaught exception 'NSRangeException', reason: '*** -[__NSArrayI objectAtIndex:]: index 2 beyond bounds for empty array'
viewDidLoad
- (void)viewDidLoad
{
    [super viewDidLoad];

    self.resultController = [DataEngine sharedInstance].postsFetchedResultController;
    self.resultController.delegate = self;
    [self.resultController performFetch:nil];

    [self.tableView reloadData];

    [[DataEngine sharedInstance] fetchInBackground];
}
Result Controller Delegate
#pragma mark - NSFetchedResultsControllerDelegate Methods -

- (void)controllerWillChangeContent:(NSFetchedResultsController *)controller
{
    [self.tableView beginUpdates];
}

- (void)controllerDidChangeContent:(NSFetchedResultsController *)controller
{
    [self.tableView endUpdates];
}

- (void)controller:(NSFetchedResultsController *)controller
   didChangeObject:(id)anObject
       atIndexPath:(NSIndexPath *)indexPath
     forChangeType:(NSFetchedResultsChangeType)type
      newIndexPath:(NSIndexPath *)newIndexPath
{
    switch (type)
    {
        case NSFetchedResultsChangeInsert:
            [self.tableView insertRowsAtIndexPaths:@[indexPath]
                                  withRowAnimation:UITableViewRowAnimationAutomatic];
            break;

        case NSFetchedResultsChangeUpdate:
            [self.tableView reloadRowsAtIndexPaths:@[indexPath]
                                  withRowAnimation:UITableViewRowAnimationAutomatic];
            break;

        case NSFetchedResultsChangeDelete:
            [self.tableView deleteRowsAtIndexPaths:@[indexPath]
                                  withRowAnimation:UITableViewRowAnimationAutomatic];
            break;

        case NSFetchedResultsChangeMove:
            [self.tableView moveRowAtIndexPath:indexPath toIndexPath:newIndexPath];
            break;

        default:
            break;
    }
}
table view
#pragma mark - UITableView Delegate & Datasrouce -

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
    return self.resultController.fetchedObjects.count;
}

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    return [self cellForRowAtIndexPath:indexPath];
}
 解决方案 
In one of my NSManagedObject subclasses I had the follwiing code which was causing the issue. NSSets are automatically initialized on NSManagedObejcts and there is no need to initialize them.
- (void)awakeFromFetch
{
    if (!self.comments)
        self.comments = [NSMutableSet set];

    if (!self.medias)
        self.medias = [NSMutableSet set];
}
Another problem was that during insert indexPath is null, I had to use newIndexPath instead
case NSFetchedResultsChangeInsert:
    [self.tableView insertRowsAtIndexPaths:@[newIndexPath]
                          withRowAnimation:UITableViewRowAnimationAutomatic];
    break;
                        
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