NSFetchedResultsController加载整个数据和不良性能

Question

我有一个包含8000多个条目的大型数据库。我想在tableview中加载并列出。我用了NSFetchedResultsController。除了糟糕的表现之外，它的工作正常。我找到了教程here

并在performFetch:方法中添加了viewDidLoad:方法。但是加载视图需要2-3秒。

这是我的代码。

- (void)loadFetchResultsController {
    NSError *error;
    if (![[self fetchedResultsController] performFetch:&error]) {
        // Update to handle the error appropriately.
        NSLog(@"Error occurs while fetching the foods with fetch results controller %@, %@", error, [error userInfo]);
        exit(-1);
    }
}

- (NSFetchedResultsController *)fetchedResultsController
{
    if (isSearching)
    {
        [NSFetchedResultsController deleteCacheWithName:@"SearchResults"];
    }
    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
    NSEntityDescription *entity = [NSEntityDescription
                                   entityForName:@"Food" inManagedObjectContext:_managedObjectContext];
    NSPredicate *hiddenPredicate = [NSPredicate predicateWithFormat:@"hidden == %@",[NSNumber numberWithBool:NO]];
    if (isSearching)
    {
        hiddenPredicate = [NSPredicate predicateWithFormat:@"(hidden == %@) AND (name contains[cd] %@ OR foodDescription contains[cd] %@)",[NSNumber numberWithBool:NO], searchTerm,searchTerm];
    }
    [fetchRequest setEntity:entity];
    [fetchRequest setPredicate:hiddenPredicate];

    NSSortDescriptor *sort = [[NSSortDescriptor alloc]
                              initWithKey:@"name" ascending:YES];
    [fetchRequest setSortDescriptors:[NSArray arrayWithObject:sort]];

    [fetchRequest setFetchBatchSize:20];

    NSFetchedResultsController *theFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:_managedObjectContext sectionNameKeyPath:@"name.stringGroupByFirstInitial" cacheName:(isSearching) ? @"SearchResults" : @"Root"];
    _fetchedResultsController = theFetchedResultsController;
    _fetchedResultsController.delegate = self;

    return _fetchedResultsController;
}

我使用了这些工具，发现调用performFetch：方法会在viewDidLoad:调用时第一次加载整个数据。

我的food数据模型是这样的：

任何提高性能和摆脱延迟的想法..任何帮助都将不胜感激。

Answer 1

我认为您需要为获取请求设置提取限制，而不仅仅是批量大小。尝试调用[fetchRequest setFetchLimit：20];看看是否有帮助。这应该导致获取前20个记录。然后，当用户滚动浏览您的数据时，请进行其他获取请求以获取更多数据。