objective-c - didChangeObject : not called of NSFetchedResultsController

Question

我几乎尝试了所有方法，但无法弄清楚哪里出了问题。我有一个 NSFetchedResultsController 并从核心数据中获取一些帖子。然后我有一种方法，可以将新帖子插入同一上下文并保存上下文。通常情况下，现在应该调用 didChangeObject: 方法，但实际上并没有。我有一个类似的 View Controller ，我在不同的表(=nsmanaged 对象)上做了基本相同的操作，并且成功调用了 didChangeObject: 方法。

到目前为止我尝试了什么:

• 为此 View Controller 创建了另一个上下文

• 移除了 NSFetchedResultsController 的缓存

以下方法从核心数据数据库中提取数据并将其“存储”到 NSFetchedResultsController(变量:controller)中。

//reloading newsgroups from coredata
- (void)reloadNewsgroupsFromCoreData
{    
    //creating fetch request
    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] initWithEntityName:@"Post"];

    //sorting by transient date (hour and secons cutted off)
    NSSortDescriptor *sortByDate = [[NSSortDescriptor alloc] initWithKey:@"dateCreatedTransient" ascending:NO];
    NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:sortByDate, nil];
    [fetchRequest setSortDescriptors:sortDescriptors];

    //where clause
    [fetchRequest setPredicate:[NSPredicate predicateWithFormat:@"ref_subscribed_newsgroup == %@ AND references == nil", self.newsgroup]];

    //setting fetchrequest
    self.controller = [[NSFetchedResultsController alloc]
                       initWithFetchRequest:fetchRequest
                       managedObjectContext:self.context
                       sectionNameKeyPath:@"dateCreatedForSections"
                       cacheName:nil]; //todo, maybe add a cache here!

    //fetch
    NSError *error;
    [self.controller performFetch:&error];

    if (error) {
        NSLog(@"%@", error);
    }
}

此外，根据文档，我将 NSFetchedResultsController 的委托(delegate)设置为我的 View Controller (这与上述 fetch 方法所在的位置相同)。

在viewDidLoad中:

self.controller.delegate = self;

然后我实现了协议(protocol)中的方法，还有 didChangeObject:

- (void)controller:(NSFetchedResultsController *)controller didChangeObject:(id)anObject atIndexPath:(NSIndexPath *)indexPath forChangeType:(NSFetchedResultsChangeType)type newIndexPath:(NSIndexPath *)newIndexPath {    
    UITableView *tableView = self.tableView;   

  // I HAVE ADDED A BREAKPOINT HERE BUT IT NEVER STOPS HERE.

    switch(type) {

        case NSFetchedResultsChangeInsert:
            [tableView insertRowsAtIndexPaths:[NSArray arrayWithObject:newIndexPath] withRowAnimation:UITableViewRowAnimationFade];

            break;
        case NSFetchedResultsChangeDelete:
            [tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade];
            break;

        case NSFetchedResultsChangeUpdate:
            [self configureCell:[tableView cellForRowAtIndexPath:indexPath]
                    atIndexPath:indexPath];

            break;

        case NSFetchedResultsChangeMove:
            [tableView deleteRowsAtIndexPaths:[NSArray
                                               arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade];
            [tableView insertRowsAtIndexPaths:[NSArray
                                               arrayWithObject:newIndexPath] withRowAnimation:UITableViewRowAnimationFade];
            break;
    }

}

然后我有另一种方法将一些帖子存储到核心数据中。我认为这很重要:此方法是通过另一个线程的委托(delegate)调用的。 (服务器连接使用 performSelectorOnMainThread:... 调用它)

- (void)storeIntoCoreData:(NSArray*)postsArray
{ 
...
        Post *entity = [NSEntityDescription insertNewObjectForEntityForName: @"Post" inManagedObjectContext:context];

        entity.inReply = dummy.in_reply;
        entity.body = dummy.body;
        entity.email = dummy.email;
        entity.from = dummy.from;
        entity.messageIdentifier = dummy.message_identifier;
        entity.references = dummy.references;
        entity.subject = dummy.subject;
        entity.dateCreated = dummy.date;
        entity.unread = [NSNumber numberWithInt:1];
...
    [self.context save:&error];
    if (error)
    {
        NSLog(@"error: %@", error);
    }

// IMPORTANT: CURRENTLY I AM CALLING THIS METHOD AGAIN HERE, WHICH 
// FETCHES ALL POSTS OUT OF CORE DATA.
// THIS IS SO UGLY AND NOT PERFORMANT. 
// THEN I INVOKE RELOADDATA ON THE TABLEVIEW TO RELOAD THE ENTIRE TABLE
// BUT THERE WAS JUST ONE INSERT SO A ENTIRE RELOAD WOULD NOT BE NECESSARY. 
    [self reloadNewsgroupsFromCoreData];
    [self.tableView reloadData];

// I HAVE TO DO THIS BECAUSE THE didChangeObject METHOD GETS NOT CALLED.
}

有没有人提示或建议哪里可能是错的？

感谢和问候，克里斯

Answer 1

问题是您在 viewDidLoad 中设置 Controller 委托(delegate)，然后在 reloadNewsgroupsFromCoreData 中分配一个新 Controller 。您新分配的 Controller 没有设置委托(delegate)。尝试直接在 reloadNewsgroupsFromCoreData 中设置委托(delegate)。

您通常不希望在数据发生变化时分配新的 NSFetchedResultsController。使用 NSFetchedResultsController 的全部目的是在发生变化时通过 NSFetchedResultsControllerDelegate 获取委托(delegate)消息。如果您的获取请求发生变化，您只需要分配一个新的 NSFetchedResultsController。我建议再看看 Apple Docs .