具有 fetchedResultsController 的表视图在应用程序重新启动或视图重新加载之前不会更新新内容

Question

我的表视图没有被nsfetchedresultscontroller中拉取的数据填充，直到应用程序重新启动或我转到另一个视图控制器并返回。我以前从未遇到过这个问题，很奇怪。

法典：

- (void)viewDidLoad {
    [super viewDidLoad];
    self.tableView.contentInset = UIEdgeInsetsMake(0, 0, 60, 0);
    [super viewDidLoad];

    NSError *error;
    if (![[self fetchedResultsController] performFetch:&error]) {
        // Update to handle the error appropriately.
        NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
        exit(-1);  // Fail
    }

    UIRefreshControl *refresh = [[UIRefreshControl alloc] init];
    [refresh addTarget:self
                action:@selector(refresh)
      forControlEvents:UIControlEventValueChanged];
    self.refreshControl = refresh;
    UITableViewController *tableVC = [[UITableViewController alloc]initWithStyle:UITableViewStylePlain];
    [tableVC setTableView:self.tableView];
    tableVC.refreshControl = self.refreshControl;
    [self.tableView setContentOffset:CGPointMake(0.0f, -60.0f)
                                          animated:YES];
    [self getPosts];

    // Do any additional setup after loading the view.
}

getPosts 提取表视图的所有帖子并将它们保存到 coredata 中。

-(void)getPosts
{
    [self.refreshControl beginRefreshing];
    [self.postsController getPostsFeedWithCompletion:^(BOOL complete, NSArray *posts) {
        [self.refreshControl endRefreshing];
    } failure:^(NSString *message) {
        [self.refreshControl endRefreshing];
        ALAlertBanner *alert = [ALAlertBanner alertBannerForView:self.view
                                                           style:ALAlertBannerStyleFailure
                                                        position:ALAlertBannerPositionTop
                                                           title:@"Error"
                                                        subtitle:@"Error retrieving posts, please try again."];
        [alert show];
    }];
}

getPostsFeedWithComplete方法：

-(void)getPostsFeedWithCompletion:(void (^)(BOOL complete, NSArray *posts))complete
                          failure:(void (^)(NSString *message))failure
{
    [[APIManager sharedManager] getPath:@"posts/feed"
                             parameters:nil
                                success:^(AFHTTPRequestOperation *operation, id responseObject) {
                                    DLog(@"response: %@", responseObject);
                                    NSArray __block *posts;
                                    [MagicalRecord saveWithBlock:^(NSManagedObjectContext *localContext){
                                        posts = [self createPosts:responseObject[@"posts"] inContext:localContext];
                                    } completion:^(BOOL success, NSError *error) {
                                        if(complete){
                                            complete(YES, posts);
                                        }
                                    }];
                                }
                                failure:^(AFHTTPRequestOperation *operation, NSError *error) {
                                    DLog(@"error: %@", error);
                                    if(failure){
                                        failure(@"Error retrieving posts");
                                    }
                                }];
}

这是 nsfetchedresultsController 实例化

- (NSFetchedResultsController *)fetchedResultsController {
    if (_fetchedResultsController != nil) {
        return _fetchedResultsController;
    }
    NSManagedObjectContext *context = [NSManagedObjectContext MR_contextForCurrentThread];
    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
    NSEntityDescription *entity = [NSEntityDescription
                                   entityForName:@"Post" inManagedObjectContext:context];
    [fetchRequest setEntity:entity];
    NSArray  *following = [[SessionManager getInstance].currentLoggedInUser.follows allObjects];
    NSMutableArray *predicateArray = [NSMutableArray array];
    NSDate *now = [NSDate date];
    [predicateArray addObject:[NSPredicate predicateWithFormat:@"account IN %@", following]];
    [predicateArray addObject:[NSPredicate predicateWithFormat:@"expiration > %@", now]];
    NSCompoundPredicate *filterPredicate = [NSCompoundPredicate andPredicateWithSubpredicates:predicateArray];
    [fetchRequest setPredicate:filterPredicate];
    [fetchRequest setFetchBatchSize:20];

    NSSortDescriptor *sort = [[NSSortDescriptor alloc]
                              initWithKey:@"expiration" ascending:YES];
    [fetchRequest setSortDescriptors:[NSArray arrayWithObject:sort]];
    [fetchRequest setFetchBatchSize:20];
    NSFetchedResultsController *theFetchedResultsController =
    [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest
                                        managedObjectContext:context
                                          sectionNameKeyPath:nil
                                                   cacheName:nil];
    self.fetchedResultsController = theFetchedResultsController;
    _fetchedResultsController.delegate = self;
    return _fetchedResultsController;
}

这是来自MagicalRecord Save的日志：

[NSManagedObjectContext(MagicalSaves) MR_saveWithOptions:completion:](0x7ffcea601bd0) → Saving <NSManagedObjectContext (0x7ffcea601bd0): *** UNNAMED ***> on *** BACKGROUND THREAD ***
[NSManagedObjectContext(MagicalSaves) MR_saveWithOptions:completion:](0x7ffcea601bd0) → Save Parents? 1
[NSManagedObjectContext(MagicalSaves) MR_saveWithOptions:completion:](0x7ffcea601bd0) → Save Synchronously? 1
[NSManagedObjectContext(MagicalRecord) MR_contextWillSave:](0x7ffcea601bd0) Context UNNAMED is about to save. Obtaining permanent IDs for new 22 inserted objects
[NSManagedObjectContext(MagicalSaves) MR_saveWithOptions:completion:](0x7ffceba008f0) → Saving <NSManagedObjectContext (0x7ffceba008f0): *** DEFAULT ***> on *** BACKGROUND THREAD ***
[NSManagedObjectContext(MagicalSaves) MR_saveWithOptions:completion:](0x7ffceba008f0) → Save Parents? 1
[NSManagedObjectContext(MagicalSaves) MR_saveWithOptions:completion:](0x7ffceba008f0) → Save Synchronously? 1
[NSManagedObjectContext(MagicalRecord) MR_contextWillSave:](0x7ffceba008f0) Context DEFAULT is about to save. Obtaining permanent IDs for new 22 inserted objects
[NSManagedObjectContext(MagicalSaves) MR_saveWithOptions:completion:](0x7ffcea746c10) → Saving <NSManagedObjectContext (0x7ffcea746c10): *** BACKGROUND SAVING (ROOT) ***> on *** MAIN THREAD ***
[NSManagedObjectContext(MagicalSaves) MR_saveWithOptions:completion:](0x7ffcea746c10) → Save Parents? 1
[NSManagedObjectContext(MagicalSaves) MR_saveWithOptions:completion:](0x7ffcea746c10) → Save Synchronously? 1
[NSManagedObjectContext(MagicalRecord) MR_contextWillSave:](0x7ffcea746c10) Context BACKGROUND SAVING (ROOT) is about to save. Obtaining permanent IDs for new 22 inserted objects
_70-[NSManagedObjectContext(MagicalSaves) MR_saveWithOptions:completion:]_block_invoke21(0x7ffcea746c10) → Finished saving: <NSManagedObjectContext (0x7ffcea746c10): *** BACKGROUND SAVING (ROOT) ***> on *** MAIN THREAD ***

Answer 1

原来这是我的谓词的问题。
NSArray *follow在FRC的getter中被硬设置，但在getPosts api调用完成之前它是空的。