Core data 核心数据：在多线程iOS应用程序中实现多个NSManagedObject和一个NSFetchedResultsController会让人非常困惑

我有一个例程，可以在后台获取RSS条目，并将它们插入我的NSManagedObjectContext（如果还没有）

我的问题是该对象找不到重复或崩溃，这取决于我使用的

NSManagedObjectContext

。。。请帮帮我

这是简化的

.h

    @interface AsyncFetchEngine : NSObject <NSXMLParserDelegate,NSFetchedResultsControllerDelegate>
    @property (strong, nonatomic) dispatch_queue_t rssParserQueue;
    @property (strong, nonatomic) NSMutableArray *uRLsToFetch;
    @property (strong, nonatomic) NSManagedObjectContext *managedObjectContext;
    @property (strong, nonatomic) NSManagedObjectContext *childManagedObjectContext;
    @property (strong, nonatomic) NSFetchedResultsController *fetchedResultsController;

    - (Boolean) isAlreadyInTheFetchQueue:(Feed *)feed;
    - (void) fetchPosts:(Feed *)feed;
    - (void) createPostInFeed:(Feed*)feed withTitle:(NSString *)title withContent:(NSString *)content withURL:(NSString *)url withDate:(NSDate *)date;

获取方法： 注意：不确定使用哪个MOC来确定localFeed，_managedObjectContext会使应用程序崩溃

    - (void) fetchPosts:(Feed *)feed
    {
        if (!_childManagedObjectContext.parentContext) {
            [_childManagedObjectContext setParentContext:self.managedObjectContext];
        }

        if ([self isAlreadyInTheFetchQueue:feed]) {
            NSLog(@"AsyncFetchEngine::fetchPosts> \"%@\" is already in the fetch queue", feed.name);
            return;
        }
        [_uRLsToFetch addObject:feed];
        NSURL *url=[NSURL URLWithString:feed.rss];
        NSURLRequest *req = [[NSURLRequest alloc] initWithURL:url];
        if (![NSURLConnection canHandleRequest:req]) {
            return;
        }

        Feed *localFeed = ((Feed *)[_childManagedObjectContext existingObjectWithID:[feed objectID] error:nil]);

        dispatch_async(_rssParserQueue, ^{
            NSLog(@"AsyncFetchEngine::fetchPosts> Opening %@", feed.rss);

            [RSSParser parseRSSFeedForRequest:req success:^(NSArray *feedItems)
             {
                 for(RSSItem *i in feedItems)
                 {
                     [self createPostInFeed:localFeed withTitle:i.title withContent:(i.content?i.content:i.itemDescription) withURL:[i.link absoluteString] withDate:(i.pubDate?i.pubDate:[NSDate date])];
                 }
                 NSLog(@"AsyncFetchEngine::fetchPosts> Found %d items", [feedItems count]);
                 [_uRLsToFetch removeObject:feed];
             }
                                      failure:^(NSError *error)
             {
                 NSLog(@"AsyncFetchEngine::fetchPosts> RSSParser lost it: %@", [error localizedDescription]);
             }];
        });
    }

    - (Boolean) isAlreadyInTheFetchQueue:(Feed *)feed
    {
        Feed *f=nil;
        for (f in _uRLsToFetch) {
            if ([f isEqual:feed]){
                return YES;
            }
        }
        return NO;
    }

NSFECTRESSULTSCONTROLLER，我需要这样吗

    - (NSFetchedResultsController *)fetchedResultsController
    {
        if (_fetchedResultsController != nil) {
            return _fetchedResultsController;
        }

        NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
        // Edit the entity name as appropriate.

    // Note: I originally tried to use the main MOC here, but it also used to crash the app.

        NSEntityDescription *entity = [NSEntityDescription entityForName:@"Post" inManagedObjectContext:_childManagedObjectContext];
        [fetchRequest setEntity:entity];

        // Set the batch size to a suitable number.
        [fetchRequest setFetchBatchSize:20];

        // Edit the sort key as appropriate.
        NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"date" ascending:NO];
        NSArray *sortDescriptors = @[sortDescriptor];

        [fetchRequest setSortDescriptors:sortDescriptors];
        /* NSPredicate *predicate =[NSPredicate predicateWithFormat:@"feed.rss LIKE '%@'",  _detailItem.rss];
         [fetchRequest setPredicate:predicate]; */

        // Edit the section name key path and cache name if appropriate.
        // nil for section name key path means "no sections".
        NSFetchedResultsController *aFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:self.managedObjectContext sectionNameKeyPath:nil cacheName:nil];
        aFetchedResultsController.delegate = self;
        _fetchedResultsController = aFetchedResultsController;

        return _fetchedResultsController;
    }

根据转储堆栈，它通常在这种方法中的某个地方崩溃。 如果它没有崩溃，我将我的帖子添加到（空）类别中

    - (void)createPostInFeed:(Feed*)feed withTitle:(NSString *)title withContent:(NSString *)content withURL:(NSString *)url withDate:(NSDate *)date
    {
        [_childManagedObjectContext performBlockAndWait:^{
            NSError *error = nil;
            if (![self.fetchedResultsController performFetch:&error]) {
                NSLog(@"Error in refetch: %@",[error localizedDescription]);
                abort();
            }
        }];
        NSLog(@"AsyncFetchEngine.h: Searching similar posts among %d", [[self.fetchedResultsController fetchedObjects] count]);
        Boolean found=NO;
        NSPredicate *predicate=[NSPredicate predicateWithFormat:@"title == %@ AND url == %@ AND feed == %@", title, url, feed];
        NSArray *similarPosts = [_fetchedResultsController.fetchedObjects filteredArrayUsingPredicate:predicate];

        if ([similarPosts count] > 0)
        {
            NSLog(@"\n\n\n\t\tAsyncFetchEngine::fetchPosts> Skipping %@ (%@)", title, url);
        } else {
            NSLog(@"\n\n\n\t\tAsyncFetchEngine::fetchPosts> Putting new post in %@", feed.name);
            NSEntityDescription *postEntityDescription = [NSEntityDescription entityForName:@"Post"
                                                                         inManagedObjectContext:_childManagedObjectContext];
            [_childManagedObjectContext performBlock:^{
                Post *initPost = (Post *)[[NSManagedObject alloc]
                                          initWithEntity:postEntityDescription
                                          insertIntoManagedObjectContext:_childManagedObjectContext];
                initPost.title = title;
                initPost.url = url;
                initPost.excerpt = content;
                initPost.date = date;
                initPost.read = nil;
                initPost.feed = feed;

                NSError *error;
                if (![_childManagedObjectContext save:&error])
                {
                    NSLog(@"[createPost] Error saving context: %@", error);
                }
                NSLog(@"Created: %@ (%@)", title, url);
                //[[NSNotificationCenter defaultCenter] postNotificationName:@"NewPostAdded" object:self];
            }];

        }
    }

因此，我的问题是：

• 当我有多个MOC时，我是否从主控室取回并给孩子写信
• 我应该如何分别使用以上这些

---

谢谢

回答我自己的问题是为了最终帮助另一个新手

使用Coredata检查NSOperationQueue。 有一个很好的例子

    - (void)createPostInFeed:(Feed*)feed withTitle:(NSString *)title withContent:(NSString *)content withURL:(NSString *)url withDate:(NSDate *)date
    {
        [_childManagedObjectContext performBlockAndWait:^{
            NSError *error = nil;
            if (![self.fetchedResultsController performFetch:&error]) {
                NSLog(@"Error in refetch: %@",[error localizedDescription]);
                abort();
            }
        }];
        NSLog(@"AsyncFetchEngine.h: Searching similar posts among %d", [[self.fetchedResultsController fetchedObjects] count]);
        Boolean found=NO;
        NSPredicate *predicate=[NSPredicate predicateWithFormat:@"title == %@ AND url == %@ AND feed == %@", title, url, feed];
        NSArray *similarPosts = [_fetchedResultsController.fetchedObjects filteredArrayUsingPredicate:predicate];

        if ([similarPosts count] > 0)
        {
            NSLog(@"\n\n\n\t\tAsyncFetchEngine::fetchPosts> Skipping %@ (%@)", title, url);
        } else {
            NSLog(@"\n\n\n\t\tAsyncFetchEngine::fetchPosts> Putting new post in %@", feed.name);
            NSEntityDescription *postEntityDescription = [NSEntityDescription entityForName:@"Post"
                                                                         inManagedObjectContext:_childManagedObjectContext];
            [_childManagedObjectContext performBlock:^{
                Post *initPost = (Post *)[[NSManagedObject alloc]
                                          initWithEntity:postEntityDescription
                                          insertIntoManagedObjectContext:_childManagedObjectContext];
                initPost.title = title;
                initPost.url = url;
                initPost.excerpt = content;
                initPost.date = date;
                initPost.read = nil;
                initPost.feed = feed;

                NSError *error;
                if (![_childManagedObjectContext save:&error])
                {
                    NSLog(@"[createPost] Error saving context: %@", error);
                }
                NSLog(@"Created: %@ (%@)", title, url);
                //[[NSNotificationCenter defaultCenter] postNotificationName:@"NewPostAdded" object:self];
            }];

        }
    }