Ios FetchedResultController中没有节

我插入并保存托管对象：

  MyAppDelegate *appDelegate = (MyAppDelegate *)[[UIApplication sharedApplication] delegate];
  NSManagedObjectContext *context = [appDelegate managedObjectContext];

  MyCity* city = (MyCity*)[NSEntityDescription insertNewObjectForEntityForName:@"City" inManagedObjectContext:context];
  city.cityId = dict[@"id"];
  city.cityName = dict[@"name"];

  NSError *error;
  if (![context save:&error]) {
    NSLog(@"error: %@", [error localizedDescription]);
  }

我执行FRC请求：

  _fetchedResultsController = nil;
  if (![[self fetchedResultsController] performFetch:&error]) {
    NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
  }

这是我的财务报告准则：

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

  MyAppDelegate *appDelegate = (MyAppDelegate *)[[UIApplication sharedApplication] delegate];
  NSManagedObjectContext *context = [appDelegate managedObjectContext];

  NSEntityDescription *entity = [NSEntityDescription entityForName:@"City"
                                          inManagedObjectContext: context];
  NSSortDescriptor *sd1 = [[NSSortDescriptor alloc] initWithKey:@"cityName" ascending:YES];
  NSArray *sortDescriptors = [NSArray arrayWithObjects:sd1, nil];

  NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
  [fetchRequest setEntity:entity];
  [fetchRequest setSortDescriptors:sortDescriptors];
  [fetchRequest setFetchBatchSize:10];

  NSFetchedResultsController *theFetchedResultsController =
  [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest
                                    managedObjectContext:context
                                      sectionNameKeyPath: @"cityName"
                                               cacheName: @"cache"];
  [self setFetchedResultsController: theFetchedResultsController];
  _fetchedResultsController.delegate = self;

  return _fetchedResultsController;
}

在

performFetch

之后，我看到：

_fetchedResultsController.fetchedObjects //array of MyCity objects
_fetchedResultsController.sections //empty array

为什么fetchedResultsController.sections为空

当我不使用

[context save:&error]

时，我可以在_fetchedResultsController.sections中看到对象数组

---

在我的代码中保存上下文是否有问题？如何保存nsmanagedobject和nsmanagedcontext？

可能

dict

为空，因此

cityName

为空，并且没有节标题

此外，您应该持有对托管对象上下文的引用，而不是反复转到应用程序委托获取它

我还建议您在不使用

fetchBatchSize

和

cache:nil

的情况下测试代码，并在以后进行优化

还要注意的是，通常的模式是在返回FRC之前懒洋洋地创建FRC时进行获取。然后，您可以

nil

it out来生成获取，或者对现有实例调用

performFetch