删除对象时为null indexPaths

时间:2013-10-10 02:00:10

标签: ios core-data nsfetchedresultscontroller

我无法解决这个问题,但是当我从NSFetchedResultsController删除对象时,我似乎有一个空索引路径。

当我删除我的对象时,我这样做:

- (void)tableView:(UITableView *)tableView commitEditingStyle:(UITableViewCellEditingStyle)editingStyle forRowAtIndexPath:(NSIndexPath *)indexPath {
    if (editingStyle == UITableViewCellEditingStyleDelete) {
        // Delete the object
        NSManagedObjectContext *context = [self.fetchedResultsController managedObjectContext];
        [context deleteObject:[self.fetchedResultsController objectAtIndexPath:indexPath]];

        [self saveContext];
    }
}

设置NSFetchedResultsController

- (NSFetchedResultsController *)fetchedResultsController {
    if (_fetchedResultsController != nil) {
        return _fetchedResultsController;
    }
    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
    [fetchRequest setFetchBatchSize:20];

    NSEntityDescription *entity = [NSEntityDescription entityForName:@"Route" inManagedObjectContext:self.managedObjectContext];
    [fetchRequest setEntity:entity];

    NSSortDescriptor *nameSort = [[NSSortDescriptor alloc] initWithKey:@"name" ascending:YES selector:@selector(localizedCaseInsensitiveCompare:)];
    NSArray *sortDescriptors = @[nameSort];
    [fetchRequest setSortDescriptors:sortDescriptors];

    NSFetchedResultsController *aFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:self.managedObjectContext sectionNameKeyPath:nil cacheName:@"Routes"];
    self.fetchedResultsController = aFetchedResultsController;
    self.fetchedResultsController.delegate = self;

    NSError *error = nil;
    if (![self.fetchedResultsController performFetch:&error]) {
        NSLog(@"Unresolved error with NSFetchedResultsController: %@", [error description]);
        abort();
    }

    return _fetchedResultsController;
}

这是发生故障的地方:

- (void)controller:(NSFetchedResultsController *)controller didChangeObject:(id)anObject atIndexPath:(NSIndexPath *)indexPath forChangeType:(NSFetchedResultsChangeType)type newIndexPath:(NSIndexPath *)newIndexPath {

    switch (type) {
            // Data was inserted - insert the data into the table view
        case NSFetchedResultsChangeInsert: {
            [self.savedRoutesTableView insertRowsAtIndexPaths:@[newIndexPath] withRowAnimation:UITableViewRowAnimationAutomatic];

            break;
        }
            // Data was deleted - delete the data from the table view
        case NSFetchedResultsChangeDelete: {
            [self.savedRoutesTableView deleteRowsAtIndexPaths:@[indexPath] withRowAnimation:UITableViewRowAnimationAutomatic];
            break;
        }
        case NSFetchedResultsChangeUpdate: {
            SavedRoutesTableViewCell *cell = (SavedRoutesTableViewCell *)[self.savedRoutesTableView cellForRowAtIndexPath:indexPath];
            [cell configureCellWithRoute:[controller objectAtIndexPath:newIndexPath]];
            break;
        }
        case NSFetchedResultsChangeMove: {
            [self.savedRoutesTableView deleteRowsAtIndexPaths:@[indexPath] withRowAnimation:UITableViewRowAnimationAutomatic];
            [self.savedRoutesTableView insertRowsAtIndexPaths:@[newIndexPath] withRowAnimation:UITableViewRowAnimationAutomatic];
            break;
        }
        default:
            break;
    }
}

在didChangeObject方法中,我的indexPath和newIndexPath都是nil。我可以NSLog我的对象,我确实看到了实体。它在[self.savedRoutesTableView deleteRowsAtIndexPaths:@[indexPath] withRowAnimation:UITableViewRowAnimationAutomatic];方法中崩溃,但有例外:

CoreData: error: Serious application error.  Exception was caught during Core Data change processing.  This is usually a bug within an observer of NSManagedObjectContextObjectsDidChangeNotification.  *** -[__NSPlaceholderArray initWithObjects:count:]: attempt to insert nil object from objects[0] with userInfo (null)

保存此对象时,我将其保存为:

self.route.name = routeName;
NSManagedObjectContext *tempContext = [self.route managedObjectContext];

[tempContext performBlock:^{
        NSError *error = nil;
        if (![tempContext save:&error]) {
            NSLog(@"an error occurred: %@", [error localizedDescription]);
        }

        [self.managedObjectContext performBlock:^{
            NSError *error = nil;
            if (![_managedObjectContext save:&error]) {
                NSLog(@"error in main context: %@", [error localizedDescription]);
            }
        }];
    }];

我不确定在哪里调试它,因为NSFetchedResultsController只是没有返回已删除对象的indexPath。有什么想法吗?提前谢谢。

修改 好吧,我发现导致错误的罪魁祸首,但我不知道为什么会这样。基本上我有一个ViewController,它接收来自主MOC的Route实体,如果它正在编辑路径,或者如果你正在创建一个新路由,它会插入一个新实体。所以在那个viewController中,如果我正在编辑路由,因为我正在尝试使用两个MOC,一个temp和一个main用于其父级,所以如果用户决定取消而不创建新路由,我可以轻松丢弃东西,我需要通过该路由转移到其他上下文,以制作我工作的其他代码。所以“转移”看起来像:

    NSManagedObjectContext *moc = _route.managedObjectContext;
    NSManagedObjectID *routeId = [_route objectID];
    self.tempContext = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSPrivateQueueConcurrencyType];
    self.tempContext.parentContext = moc;
    NSManagedObject *localRoute = [self.tempContext objectWithID:routeId];
    self.route = localRoute;

使用此代码,我在现有路径上添加位置现在可以使位置处于相同的上下文中,但不知何故,它会混淆从主MOC中删除现有路径。不确定为什么以及最佳解决方案是什么。

2 个答案:

答案 0 :(得分:0)

NSManagedObjectContext *moc = _route.managedObjectContext;
NSManagedObjectID *routeId = [_route objectID];
self.tempContext = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSPrivateQueueConcurrencyType];
self.tempContext.parentContext = moc;
NSManagedObject *localRoute = [self.tempContext objectWithID:routeId];
self.route = localRoute;

必须获得与路线相关的上下文。

答案 1 :(得分:0)

遇到同样的问题并通过确保NSFetchedResultsController始终使用相同的NSManagedContext来解决它。例如,如果您使用fetch控制器从数据库中获取对象,并且稍后要删除该对象,请确保获取控制器使用在获取期间使用的相同托管上下文。

NSFetchedResultsController针对使用UITableView进行了优化,UITableView是用户界面组件,用户界面应始终由主线程处理,因此每次进入fetch时都无需创建新的NSManagedContext ...因此实现此代码应该解决这个问题:

@synthesize fetchedResultsController = __fetchedResultsController; @synthesize managedObjectContext = __managedObjectContext;

- (NSManagedObjectContext *)managedObjectContext
{
    if (__managedObjectContext != nil)
    {
        return __managedObjectContext;
    }

    NSPersistentStoreCoordinator *coordinator = ap.persistentStoreCoordinator;
    if (coordinator != nil)
    {
        __managedObjectContext = [[NSManagedObjectContext alloc] init];
        [__managedObjectContext setPersistentStoreCoordinator:coordinator];
    }
    return __managedObjectContext;
}

ap是指向AppDelegate的指针:

ap = [[UIApplication sharedApplication] delegate];

这段代码的作用是创建一个MOC实例,然后重用它。警告:这不是线程安全的,它不一定是(因为你应该只使用它与主线程),所以如果你错过它它将无法正常工作......

使用:

- (NSFetchedResultsController *)fetchedResultsController
{
    if (__fetchedResultsController != nil)
    {
        return __fetchedResultsController;
    }
    //create __fetchedResultsController
    // do some fetching
    return __fetchedResultsController;
}

所以当你想要填充表时:

- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
{
    return [[self.fetchedResultsController sections] count];
}
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
    return [__fetchedResultsController.fetchedObjects count];
}

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    static NSString *CellIdentifier = @"Cell";

    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
    if (cell == nil) {
        cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier];
    }

    NSManagedObject *managedObject = [__fetchedResultsController objectAtIndexPath:indexPath];

    cell.textLabel.text = [managedObject valueForKey:@"smth."];

    return cell;
}

如果您的数据集发生了变化:

__fetchedResultsController = nil;
[tableView reloadData]

包括NSFetchedResultsControllers委托方法在内的所有方法都可以正常工作,没有nil indexPaths等等......

希望我能帮助别人......