ios - NSFetchedResultsController 尝试将第 1 行插入第 0 节，但在使用 userInfo(null)更新后第 0 节中只有 0 行

Question

我将 NSFetchedResultsController 与 UITableViewController 一起使用。我成功地将新对象添加到分离 View 中的核心数据，

ParseStarterProjectAppDelegate *appDelegate = [[UIApplication sharedApplication] delegate];
NSManagedObjectContext *context = [appDelegate managedObjectContext];
NSManagedObject *newWorkout;
newWorkout = [NSEntityDescription insertNewObjectForEntityForName:@"Workouts" inManagedObjectContext:context];
[newWorkout setValue:_workOutType forKey:@"type"];
[newWorkout setValue:_boostDate forKey:@"date"];
[newWorkout setValue:_workoutText forKey:@"text"];
[newWorkout setValue:_trainerLabelOutlet.text forKey:@"text"];
NSError *error;
if (![context save:&error]) {
    NSLog(@"Whoops, couldn't save: %@", [error localizedDescription]);
}else{
    NSLog(@"saved to core data");
}

但是我得到这个错误:在调用 -controllerDidChangeContent: 期间从 NSFetchedResultsController 的委托(delegate)捕获了一个异常。尝试将第 1 行插入第 0 节，但在使用 userInfo (null) 更新后第 0 节中只有 0 行

UITableViewController中的代码:

- (NSManagedObjectContext *)managedObjectContext {
    NSManagedObjectContext *context = nil;
    id delegate = [[UIApplication sharedApplication] delegate];
    if ([delegate performSelector:@selector(managedObjectContext)]) {
        context = [delegate managedObjectContext];
    }
    return context;
}


- (NSFetchedResultsController *)fetchedResultsController {

    if (_fetchedResultsController != nil) {
        return _fetchedResultsController;
    }

    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
    NSEntityDescription *entity = [NSEntityDescription
                                   entityForName:@"Workouts" inManagedObjectContext:self.managedObjectContext];
    [fetchRequest setEntity:entity];
    NSSortDescriptor *sort = [[NSSortDescriptor alloc] initWithKey:@"date" ascending:NO];
    [fetchRequest setSortDescriptors:[NSArray arrayWithObject:sort]];
    [fetchRequest setFetchBatchSize:20];
    NSFetchedResultsController *theFetchedResultsController =
    [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest
                                        managedObjectContext:self.managedObjectContext sectionNameKeyPath:nil
                                                   cacheName:@"Root"];
    self.fetchedResultsController = theFetchedResultsController;
    _fetchedResultsController.delegate = self;
    return _fetchedResultsController;
}

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

- (void)viewDidUnload {
    self.fetchedResultsController = nil;
}

#pragma mark - Table view data source

- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
{
    // Return the number of sections.
    return [[self.fetchedResultsController sections] count];
}

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
    id  sectionInfo = [[_fetchedResultsController sections] objectAtIndex:section];
    return [sectionInfo numberOfObjects];
}

- (void)configureCell:(UITableViewCell *)cell atIndexPath:(NSIndexPath *)indexPath {
    WorkoutObject *workout = [_fetchedResultsController objectAtIndexPath:indexPath];
    cell.textLabel.text = workout.text;
    NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
    [dateFormatter setDateFormat:@"yyy-MM-dd   HH:mm"];
    NSString *dateString = [dateFormatter stringFromDate:workout.date];
    cell.detailTextLabel.text = dateString;
}

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    static NSString *CellIdentifier = @"Cell";
    CustomTableViewCell *cell =[tableView dequeueReusableCellWithIdentifier:CellIdentifier];
    // Set up the cell...
    [self configureCell:cell atIndexPath:indexPath];
    return cell;    
}

- (void)controllerWillChangeContent:(NSFetchedResultsController *)controller {
    // The fetch controller is about to start sending change notifications, so prepare the table view for updates.
    [self.tableView beginUpdates];
}

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

    UITableView *tableView = self.tableView;

    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;
    }
}

- (void)controller:(NSFetchedResultsController *)controller didChangeSection:(id )sectionInfo atIndex:(NSUInteger)sectionIndex forChangeType:(NSFetchedResultsChangeType)type {

    switch(type) {

        case NSFetchedResultsChangeInsert:
            [self.tableView insertSections:[NSIndexSet indexSetWithIndex:sectionIndex] withRowAnimation:UITableViewRowAnimationFade];
            break;

        case NSFetchedResultsChangeDelete:
            [self.tableView deleteSections:[NSIndexSet indexSetWithIndex:sectionIndex] withRowAnimation:UITableViewRowAnimationFade];
            break;
    }
}

- (void)controllerDidChangeContent:(NSFetchedResultsController *)controller {
    // The fetch controller has sent all current change notifications, so tell the table view to process all updates.
    [self.tableView endUpdates];
}

有人知道问题出在哪里吗？在过去的两天里，我试图自己弄清楚，但我无能为力。谢谢

Answer 1

我只是遇到了同样的问题 - 在我的例子中，结果证明是因为 TableView 数据源和委托(delegate)没有分配给属性检查器的导出部分中 Storyboard 上的 View Controller 。因此，没有调用 numberOfRowsForSection 和 numberOfSectionsInTableView。