ios - 如何在持久存储更改后刷新 fetchedResultsController

Question

在编程方面，我是一个周末勇士，所以我可能做错了什么......

我有一个 Split View Controller 、核心数据、nsfetchedResultsController，一切都很好。我现在可以选择让用户创建 persistentStore.sqlite 文件的备份文件。当用户从备份文件恢复时，tableview 不反射(reflect)任何变化。最重要的是，从那时起无法从 TableView 添加/删除中进行任何持久更改。当我退出应用程序并重新启动它时，备份的所有数据都在那里并且一切正常。

如何强制 tableview 从 fetched results controller 获取现在的新信息？或者我该如何强制

以下是我迄今为止尝试过但未成功的一些散点:

MasterViewController.m

- (void)viewDidLoad
{
    context = [[OSCDStackManager sharedManager] managedObjectContext];
}

[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(reloadFetchedResults) name:OSFilesUpdatedNotification object:nil];

- (void)reloadFetchedResults:(NSNotification*)note {
    NSError *error = nil;
    if (![[self fetchedResultsController] performFetch:&error]) {
        NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
        abort();
    }
    if (note) {
        [self.tableView reloadData];
    }
}


- (void)controllerDidChangeContent:(NSFetchedResultsController *)controller
{
    NSError *error = nil;
    [self.fetchedResultsController performFetch:&error];
    [self.tableView endUpdates];
    [self.tableView reloadData];
}

从 tableview 上的手动刷新下拉...

-(void) updateTable{
    context = [[OSCDStackManager sharedManager] managedObjectContext];
    NSError *error = nil;
    [self.fetchedResultsController performFetch:&error];
    //[self.tableView endUpdates];
    [self.tableView reloadData];
    [self.refreshControl endRefreshing];
}

- (void)viewWillAppear:(BOOL)animated  {
    [self.tableView reloadData];
}


- (NSFetchedResultsController *)fetchedResultsController
{
    context = [[OSCDStackManager sharedManager] managedObjectContext];
    if (_fetchedResultsController != nil) {
        return _fetchedResultsController;
    }
    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
    NSEntityDescription *entity = [NSEntityDescription entityForName:@"Event" inManagedObjectContext:context];
    [fetchRequest setEntity:entity];
    [fetchRequest setFetchBatchSize:20];
    NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"name" ascending:YES];
    NSArray *sortDescriptors = @[sortDescriptor];
    [fetchRequest setSortDescriptors:sortDescriptors];
    NSFetchedResultsController *aFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:context sectionNameKeyPath:nil cacheName:nil];
    //[NSFetchedResultsController deleteCacheWithName:@"cache"];
    aFetchedResultsController.delegate = self;
    self.fetchedResultsController = aFetchedResultsController;
    NSError *error = nil;
    if (![self.fetchedResultsController performFetch:&error]) {
        NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
        abort();
    }
    return _fetchedResultsController;
} 

即使这是我邻居的应用程序，我也不愿意告诉他在备份后终止并重新启动该应用程序...

解决方案 最终成为以下两个答案的组合，

- (void)reloadFetchedResults{
    self.fetchedResultsController = nil;
    [NSFetchedResultsController deleteCacheWithName:@"cache"];
    NSError *error = nil;
    if (![self.fetchedResultsController performFetch:&error]) {
        NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
        abort();
    }
    [self.tableView reloadData];
}

Answer 1

你有没有删除缓存？

您需要先将缓存名称设置为 fetchedResultsController(注意末尾的 cacheName 参数):

_fetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:query
                                                                managedObjectContext:context
                                                                  sectionNameKeyPath:nil
                                                                           cacheName:@"CACHE_NAME"];

然后在进行更新时删除缓存:

[NSFetchedResultsController deleteCacheWithName:@"CACHE_NAME"];

执行此操作后，通过执行以下操作再次从核心数据加载:

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