核心数据，UITableView和UISegmentedControl

4 回答

• 0

  您可以使用 NSFetchedResultsController ，当您单击片段时，只需设置不同的perdicate并再次执行提取 .

  回复于 2024-04-29T13:41:48+08:00
• 6

  我会为每个段使用单独的 NSFetchedResultsController . 这将允许您利用每个段的内置缓存并提高性能 .

  除了Apple的文档（和我的书）之外，您还可以从我在PragPub杂志上的文章_2662198中阅读它们 .

  回复于 2024-04-29T13:41:48+08:00
• 0

  为每个过滤器使用三个不同的阵列是个好主意 . 将它们缓存到某处，以便在用户选择过滤器时无延迟 . 要从CoreData商店中查找您要查找的信息，请使用NSPredicate .

  回复于 2024-04-29T13:41:48+08:00
• 0

  我使用上面Marcus的指南实现了这个（我是新手，所以它可能不是最好的方法） . 我有一个段控制器，有三个选项，分别用于'打开'，'进行中'和'关闭' .

  在ViewController.h中，为每个段选项创建一个iVar，为将存储当前控制器的主控制器创建一个iVar .

  @property (nonatomic, retain) NSFetchedResultsController *fetchedResultsController;
  
  @property (nonatomic, retain) NSFetchedResultsController *inprogressFetchedResultsController;
  @property (nonatomic, retain) NSFetchedResultsController *openFetchedResultsController;
  @property (nonatomic, retain) NSFetchedResultsController *closedFetchedResultsController;
  

  在ViewController.m中，您需要为延迟加载这些控制器创建方法，所以我总共有三个 . 除了谓词和cacheName之外，它们基本相同，我只在下面显示了一个 .

  - (NSFetchedResultsController *)closedFetchedResultsController
  {
      if (_closedFetchedResultsController != nil) {
          return _closedFetchedResultsController;
      }
  
      NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
  
      // Edit the entity name as appropriate.
      NSEntityDescription *entity = [NSEntityDescription entityForName:@"Ticket" inManagedObjectContext:self.managedObjectContext];
      [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:@"priority.name" ascending:NO];
      NSArray *sortDescriptors = @[sortDescriptor];
  
      [fetchRequest setSortDescriptors:sortDescriptors];
      NSPredicate *predicate = [NSPredicate predicateWithFormat:@"status = 'Closed'"];
      [fetchRequest setPredicate:predicate];
  
      NSFetchedResultsController *aFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:self.managedObjectContext sectionNameKeyPath:@"priority.name" cacheName:@"ClosedTickets"];
      aFetchedResultsController.delegate = self;
  
      self.closedFetchedResultsController = aFetchedResultsController;
  
      NSError *error = nil;
      if (![self.closedFetchedResultsController performFetch:&error]) {
          // Replace this implementation with code to handle the error appropriately.
          // abort() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.
          NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
          abort();
      }
  
      return _closedFetchedResultsController;
  }
  

  为您的段创建一个IBAction，以便在更改它时更改获取的结果控制器并重新加载表 .

  - (IBAction)statusChanged:(id)sender {
      switch (self.segmentControl.selectedSegmentIndex) {
          case 0:
              self.fetchedResultsController = self.inprogressFetchedResultsController;
              break;
          case 1:
              self.fetchedResultsController = self.openFetchedResultsController;
              break;
          case 2:
              self.fetchedResultsController = self.closedFetchedResultsController;
              break;
          default:
              break;
  
      }
      [self.tableView reloadData];
  }
  

  而已！

  注：我还将此行添加到我的ViewDidLoad方法中，以便它最初将正确的选项加载到fetchedResultsController中 .

  self.fetchedResultsController = self.inprogressFetchedResultsController;
  

  回复于 2024-04-29T13:41:48+08:00