Question

我已启用com.apple.CoreData.ConcurrencyDebug 1来检查Core Data并发错误。我在Swift类中有以下代码段：

lazy var context: NSManagedObjectContext! = {
    var appDelegate = UIApplication.sharedApplication().delegate as! AppDelegate
    return appDelegate.managedObjectContext!
}()

func getAllEntitiesToRootContext() -> [MyEntity]? {
    let fetchRequest = NSFetchRequest(entityName:"MyEntity")

    do {
        let fetchedResults = try context.executeFetchRequest(fetchRequest) as! [MyEntity]

        if fetchedResults.count > 0 {
            return fetchedResults
        } else {
            return nil
        }
    } catch let error as NSError {
        print("could not fetch \(error), \(error.userInfo)")
        return nil
    }
}

如果我正确理解，我从AppDelegate获得的上下文与主线程相关联，对吧？

然而，从我所拥有的另一个Objective-C课程中，我做到了：

self.myEntitiesArray = [mySwiftClass getAllEntitiesToRootContext];

我收到此错误日志：

CoreData：错误：当前线程不是此NSManagedObjectContext（0x1a25f8a0）的已识别所有者。在executeFetchRequest期间非法访问：错误：

我不明白为什么......我应该将这样的上下文与主线程相关联，并且我从主线程中调用getAllEntitiesToRootContext ...

我需要帮助。提前致谢

编辑：这些是Core Data中与AppDelegate相关的方法：

- (NSManagedObjectContext *)managedObjectContext
{
   // Returns the managed object context for the application (which is already bound to the persistent store coordinator for the application.)
   if (_managedObjectContext != nil) {
       return _managedObjectContext;
   }

   NSPersistentStoreCoordinator *coordinator = [self persistentStoreCoordinator];
   if (!coordinator) {
       return nil;
   }
   _managedObjectContext = [[NSManagedObjectContext alloc] init];
   [_managedObjectContext setPersistentStoreCoordinator:coordinator];
   return _managedObjectContext;
}

- (NSPersistentStoreCoordinator *)persistentStoreCoordinator
{
   // The persistent store coordinator for the application. This implementation creates and return a coordinator, having added the store for the application to it.
   if (_persistentStoreCoordinator != nil) {
       return _persistentStoreCoordinator;
   }

   // Create the coordinator and store

   _persistentStoreCoordinator = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:[self managedObjectModel]];
   NSURL *storeURL = [[self applicationDocumentsDirectory] URLByAppendingPathComponent:@"MyApp.sqlite"];
   NSError *error = nil;
   NSString *failureReason = @"There was an error creating or loading the application's saved data.";
   if (![_persistentStoreCoordinator addPersistentStoreWithType:NSSQLiteStoreType configuration:nil URL:storeURL options:nil error:&error]) {
       // Report any error we got.
       NSMutableDictionary *dict = [NSMutableDictionary dictionary];
       dict[NSLocalizedDescriptionKey] = @"Failed to initialize the application's saved data";
       dict[NSLocalizedFailureReasonErrorKey] = failureReason;
       dict[NSUnderlyingErrorKey] = error;
       error = [NSError errorWithDomain:@"YOUR_ERROR_DOMAIN" code:9999 userInfo:dict];
       // Replace this 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 _persistentStoreCoordinator;
}

- (NSManagedObjectModel *)managedObjectModel
{
   // The managed object model for the application. It is a fatal error for the application not to be able to find and load its model.
   if (_managedObjectModel != nil) {
      return _managedObjectModel;
   }
   NSURL *modelURL = [[NSBundle mainBundle] URLForResource:@"MyApp" withExtension:@"momd"];
  _managedObjectModel = [[NSManagedObjectModel alloc] initWithContentsOfURL:modelURL];
 return _managedObjectModel;
}

编辑2：我正在使用Xcode 7并在iOS 9设备中进行测试。

编辑3：如果我停用com.apple.CoreData.ConcurrencyDebug 1，我会从getAllEntitiesToRootContext()获取对象...我真的不明白，为什么会发生这种情况？

编辑4：我做了一些测试。如果我从Objective-C班级执行此操作：

- (void)getEntities
{
   AppDelegate *appDelegate = [[UIApplication sharedApplication] delegate];
   NSManagedObjectContext *mainContext = appDelegate.managedObjectContext;

   NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] initWithEntityName:@"MyEntity"];
   NSArray *entities = [mainContext executeFetchRequest:fetchRequest error:nil];

   for (NSManagedObject *item in entities) {
       NSLog(@"Name: %@", ((MyEntity *)item).name);
   }
}

我在调用executeFetchRequest时有时没有错误，并且日志控制台中显示了实体的名称。其他时候我也得到类似于我上面发布的核心数据错误，我在做的时候也得到了：

- (NSArray *)getEntities
{
   MyEntityDao *myEntityDao = [[MyEntityDao alloc] init];
   self.myEntities = [[myEntityDao getAllEntitiesToRootContext] mutableCopy];

   return [[NSArray arrayWithArray:self.myEntities] copy];
}

其中MyEntityDao是定义Swift和lazy var context的{{1}}类，我收到了上面发布的核心数据错误...为什么？这两个代码片段不相同吗？为什么我有时说主线程不是我从getAllEntitiesToRootContext()检索的MOC的所有者？

我真的需要帮助...

Answer 1

context.executeFetchRequest(fetchRequest)做什么？那段代码是什么样的？

在某些时候，您处于主队列以外的其他队列中。

您收到的错误表示您违反了线程限制。如果您在Xcode中有异常和错误的断点，它将显示违反规则的确切代码行以及执行它的队列。

Xcode停在什么行代码？

当Xcode停止时你在哪个队列？

我不建议关闭调试标志，它可以帮助您并让您找到线程错误。关闭它只是隐藏问题，并将导致生产中的问题与用户数据。更好地投入时间，了解正在发生的事情并正确地纠正它。

Answer 2

似乎在调用getAllEntitiesToRootContext()之前，在某些情况下我从一个不是主线程的队列中检索AppDelegate中定义的上下文，导致该上下文被初始化的原因是什么其他队列......

我感谢Leo的评论和Marcus S. Zarra的回答，谢谢。

在主线程中非法访问托管对象上下文，为什么？

2 个答案: