Question

在尝试了解有关Core Data和多线程的更多信息时，我编写了一个无法保存到核心数据的应用程序。首先是一些背景。在我的视图出现之前，我创建了托管上下文。这发生在主线：

- (void)viewWillAppear:(BOOL)animated
{
    [super viewWillAppear:animated];
    if (!self.managedObjectContext) [self useDocument];

}

- (void)useDocument
{
    NSURL *url = [[[NSFileManager defaultManager] URLsForDirectory:NSDocumentDirectory inDomains:NSUserDomainMask] lastObject];
    url = [url URLByAppendingPathComponent:MY_DOCUMENT];
    UIManagedDocument *document = [[UIManagedDocument alloc] initWithFileURL:url];

    if (![[NSFileManager defaultManager] fileExistsAtPath:[url path]]) {
        [document saveToURL:url
           forSaveOperation:UIDocumentSaveForCreating
          completionHandler:^(BOOL success) {
              if (success) {
                  NSLog(@"@@@AMRO--->managedObjectContext has been setup");
                  self.managedObjectContext = document.managedObjectContext;
                  [self refresh];
              }
          }];
    } else if (document.documentState == UIDocumentStateClosed) {
        [document openWithCompletionHandler:^(BOOL success) {
            if (success) {
                NSLog(@"@@@AMRO--->managedObjectContext has been opened");
                self.managedObjectContext = document.managedObjectContext;
                [self refresh];
            }
        }];
    } else {
        NSLog(@"@@@AMRO--->managedObjectContext has been set");
        self.managedObjectContext = document.managedObjectContext;
    }
}

当我的视图出现时，我使用这种方法从客户端获取数据。该我这样做的原因是因为我不希望我的视图被阻止作为我的客户端刷新正在发生：

        dispatch_queue_t fetchQ = dispatch_queue_create("Client Fetch", NULL);
        dispatch_async(fetchQ, ^{
            [self.managedObjectContext performBlock:^{
               dispatch_async(dispatch_get_main_queue(), ^{
                    [self reload];
                    dispatch_async(fetchQ, ^{
                        [self refreshClientInformation];
                    });
                });
            }];
        });

对refreshClientInformation的调用大约需要2分钟才能检索但是，我希望视图在此期间加载任何我有。上述方法阻止了我尽管有明确的调用，但能够保存到上下文 refreshClientInformation中的[self.managedContext save:&error] 每次客户端数据更新后。 refreshPersonalClientInformations在“客户端获取”线程队列中执行。

- (void) refreshPersonalClientInformation
{
    NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:@"CLIENT"];
    request.sortDescriptors = @[[NSSortDescriptor sortDescriptorWithKey:@"stationId" ascending:YES]];
    NSDate *twoHoursAgo = [NSDate dateWithTimeIntervalSinceNow:-2*60*60];
    request.predicate = [NSPredicate predicateWithFormat:@"conditionsUpdated < %@", twoHoursAgo];
    NSError *error = nil;

    int counter = 0;

    // Execute the fetch
    NSArray *matches = [self.managedObjectContext executeFetchRequest:request error:&error];

    // Check what happened in the fetch
    if (!matches) {  // nil means fetch failed;
        NSLog(@"ERROR: Fetch failed to find CLIENT %@ in database", DEFAULT);
    } else if (![matches count]) { // none found, so lets retrieve it below
        return;
    } else {
        for (CLIENT *client in matches) {
            NSDictionary *clientDict = [ClientFetcher clientInfo:client.clientId];

            client.name = [clientDict[NAME] description];

            client.age = [clientDict[AGE] description];
            client.updated = [NSDate date];
            if (![self.managedObjectContext save:&error]) {
                NSLog(@"@@@@@@@@@@@@@@@@@@@@@@@@@@AMRO Unresolved error %@, %@", error, [error userInfo]);
            }

            //Have to rate limit requests at no more than 10 per minute.
            NSLog(@"Sleeping for 6s");
            sleep(6);
            NSLog(@"Done sleeping for 6s");
        }
    }
}

我甚至尝试通过执行以下操作在refreshPersonalClientInfo中运行save：

 dispatch_async(dispatch_get_main_queue(), ^{
     [self.managedObjectContext save:nil];
 });

但这没有用，没有发现错误

作为一项实验，当我的视图出现时，我将线程调用更改为此核心数据最终得到保存，问题是我的视图被阻止了，我必须这样做在检索数据时等待很长时间。另外，当我最终说出来时，我的意思是在我拨打[self.managedContext save:nil]之后不会发生这种情况，但是几分钟之后：

        dispatch_queue_t fetchQ = dispatch_queue_create("Client Fetch", NULL);
        dispatch_async(fetchQ, ^{
            [self.managedObjectContext performBlock:^{
                [self refreshPersonalClientInformation];
                dispatch_async(dispatch_get_main_queue(), ^{
                    [self reload];
                });
            }];
        });

有关如何在后台线程中检索我的信息的任何建议并且能够将数据保存到磁盘，同时我仍然可以访问我的UI吗？

Answer 1

您最好创建子上下文以在后台执行所有操作：

dispatch_queue_t fetchQ = dispatch_queue_create("Client Fetch", NULL);
    dispatch_async(fetchQ, ^{
        NSManagedObjectContext *context = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSPrivateQueueConcurrencyType];
        context.parentContext = self.managedObjectContext;
        [context performBlock:^{
            [self refreshPersonalClientInformation];
            dispatch_async(dispatch_get_main_queue(), ^{
                [self reload];
            });
         }];
    });

核心数据管理上下文不在多线程环境中保存

1 个答案: