Ios 使用NSFetchedResultsController从数据库中提取会导致应用程序冻结

在我的应用程序中，在处理来自服务器的大数据时出现了冻结问题。我真的很困惑这个问题，最后我尝试了使用父子策略对coredata进行后台保存。在那之后，应用程序的速度比之前快了一点，但仍然存在小冻结。所以我认为现在的问题可能是因为获取核心数据。那么有没有办法在后台获取coredata呢？ 我已经被搜索了链接

但这对我没有帮助

   -(NSFetchedResultsController*)fetchedResultsController
 {


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

NSString *loginUser=[[NSUserDefaults standardUserDefaults] valueForKey:@"currentUser"];

AppDelegate *sharedDelegate = (AppDelegate *)[[UIApplication sharedApplication] delegate];
NSManagedObjectContext *context = [sharedDelegate managedObjectContext];
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
[fetchRequest setReturnsObjectsAsFaults:NO];
NSEntityDescription *entity = [NSEntityDescription entityForName:@"ThreadInfo"
                                          inManagedObjectContext:context];
[fetchRequest setEntity:entity];

NSSortDescriptor *sort = [[NSSortDescriptor alloc]
                          initWithKey:@"threadDate" ascending:NO];
[fetchRequest setSortDescriptors:[NSArray arrayWithObject:sort]];


NSPredicate *threadPredicate = [NSPredicate predicateWithFormat:@"userEmail == %@",loginUser];
// NSPredicate *providerPredicate = [NSPredicate predicateWithFormat:@"isReceiver == YES"];
//  NSPredicate *compoundPredicate = [NSCompoundPredicate andPredicateWithSubpredicates: @[threadPredicate, providerPredicate]];

[fetchRequest setPredicate:threadPredicate];
[fetchRequest setFetchBatchSize:5];
NSFetchedResultsController *theFetchedResultsController =
[[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest
                                    managedObjectContext:context sectionNameKeyPath:nil
                                               cacheName:nil];
_fetchedResultsController = theFetchedResultsController;
_fetchedResultsController.delegate = self;

return _fetchedResultsController;

}

Appdelegate

         - (void)saveContext
 {
NSError *error = nil;
NSManagedObjectContext *managedObjectContext = self.managedObjectContext;
if (managedObjectContext != nil) {
    if ([managedObjectContext hasChanges] && ![managedObjectContext save:&error]) {
                  NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
        abort();

  }
 }
 }

  #pragma mark - Core Data stack


- (NSManagedObjectContext *)managedObjectContext
 {


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


NSPersistentStoreCoordinator *coordinator = [self persistentStoreCoordinator];
if (coordinator != nil) {
    //        _managedObjectContext = [[NSManagedObjectContext alloc] init];
    _managedObjectContext = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSPrivateQueueConcurrencyType];

    [_managedObjectContext setPersistentStoreCoordinator:coordinator];
}
return _managedObjectContext;

 }

// Returns the managed object model for the application.
// If the model doesn't already exist, it is created from the application's model.
- (NSManagedObjectModel *)managedObjectModel
{
if (_managedObjectModel != nil) {
    return _managedObjectModel;
}

   NSURL *modelURL = [[NSBundle mainBundle] URLForResource:@"IXCoreDataModel" withExtension:@"momd"];
  _managedObjectModel = [[NSManagedObjectModel alloc] initWithContentsOfURL:modelURL];
  return _managedObjectModel;
}


- (NSPersistentStoreCoordinator *)persistentStoreCoordinator
  {

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

NSURL *storeURL = [[self applicationDocumentsDirectory]   URLByAppendingPathComponent:@"Inxed.sqlite"];

 NSError *error = nil;
_persistentStoreCoordinator = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:[self managedObjectModel]];
if (![_persistentStoreCoordinator addPersistentStoreWithType:NSSQLiteStoreType configuration:nil URL:storeURL options:nil error:&error]) {
    /*
     */
    NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
    abort();
}

return _persistentStoreCoordinator;
}

 #pragma mark - Application's Documents directory

// Returns the URL to the application's Documents directory.
   - (NSURL *)applicationDocumentsDirectory
    {

   return [[[NSFileManager defaultManager] URLsForDirectory:NSDocumentDirectory   inDomains:NSUserDomainMask] lastObject];

  }

冻结时，我通过暂停应用程序在下面的行中发现了问题

   - (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath

   {
    ThreadInfo *info=[_fetchedResultsController objectAtIndexPath:indexPath];// THIS LINE TAKES TOO MUCH TIME


if([info.isSystemMessage boolValue]){

    return 178+90+25;


} else {
     return 300;
 }

您正在处理大量数据，但一次获取所有数据，不要将数据量限制在有用的范围内。因此，在初始化

NSFetchedResultsController

时，您可能不需要提取真实对象，使用错误，它们基本上是可以的

//FRC请求
NSFetchRequest*fetchRequest=[NSFetchRequest new]；
fetchRequest.returnsObjectsAsFaults=是；//多余的，我只想说清楚
fetchRequest.fetchBatchSize=20；//甚至更少，这取决于用户可见的数据量

然后，如所示，使用

估计高度

。这允许FRC猜测您要查看的数据的大致部分，当计算出实际高度时（如您所做的），数据就在手边

---

下一件事：索引数据。您的

isSystemMessage

是否已编制索引？应该是这样。

怎么帮不了你？你做过任何分析来发现你的性能问题吗？用导致冻结的行更新了问题。请检查我已经检查了代码，但你知道我是新手，这让我更困惑。我想要的只是如何修改“fetchedResultsController”方法来处理后台抓取？不要再需要后台线程了。请看使用估计高度。