核心数据 - 在多线程之间共享NSManagedObjects [英] Core Data - sharing NSManagedObjects among multiple threads

问题描述

我遭受了在多个线程中使用单个MOC的所有后果 - 我的应用程序在随机点崩溃，因为MOC是在主线程中创建的，我还使用它在另一个线程中填充DB。
虽然代码是同步的（@synchronize）使用全局单例的应用程序崩溃。
我读到，使用单独的MOC为每个线程将使事情确定，但我还读，它被认为也是一个坏的方法来共享线程的NSManagedObjects。

I suffered all the consequences of using a single MOC in multiple threads - my app crashes at random points because the MOC is created in the main thread and I also use it to fill the DB in another thread. Though the code is synchronized (@synchronize) using a global singleton the app crashes. I read that using a separate MOC for each thread will make things ok but I also read that it is considered also a bad approach to share NSManagedObjects across threads.

我的用例如下：
1）从服务器加载并解析XML，在解析期间，我在数据库中插入每个新的NSManagedObject。这一切发生在一个单独的线程。
2）从主线程，用户与从数据库读取数据的UI交互。

My use case is the following: 1)I load and parse XML from a server and during the parsing I insert each new NSManagedObject in the database. This all happens in a separate thread. 2)From the main thread the user interacts with the UI which reads data from the database.

在这两个线程中，我使用NSManagedObjects。你怎么建议我解决这个问题？我失败多次已经。

In both threads I use NSManagedObjects. How would you suggest me to fix this? I failed multiple times already.

大多数情况下，应用程序创建了错误，表明我正在修改一个集合，枚举它，这是不真实的代码是同步的，而我我重复它没有修改发生，反之亦然 - 而我修改它我不迭代，我保存一旦我完成。

Most often the app creashed with error suggesting that I am modifying a collection while enumerating it which is not true as the code is synchronized and while I am iterating it no modifying happens and vice versa - while I modify it I don't iterate and I save once I am done.

推荐答案

p>每个线程使用一个 NSManagedObjectContext 。如果你在线程之间通信，传递 NSManagedObjectID ，这是线程安全的，并从你的线程上下文中重新获取对象。在我的应用程序中，我有时甚至为每个控制器使用一个上下文。

Use one NSManagedObjectContext per thread. If you communicate between threads, pass the NSManagedObjectID, which is thread safe, and fetch the object again from you thread context. In my apps I sometimes even use one context per controller.

要管理不同的上下文，注册 NSManagedObjectContextDidChangeNotification 。在此通知处理中，您可以通过 mergeChangesFromContextDidSaveNotification：方法将通知传递给每个上下文。此方法是线程保存，并使上下文更新其状态。

To manage the different contexts, register an Observer for the NSManagedObjectContextDidChangeNotification. Within this notification handling, you pass the notification to each of your contexts via the mergeChangesFromContextDidSaveNotification: method. This method is thread save and makes the context update its state.

之后，您必须刷新您的视图。如果你有一个基于表视图的应用程序，请查看 NSFetchedResultsController 。这有助于您使用适当的动画自动更新表。如果您不使用表格视图，则必须自己实现UI更新。

After this you have to refresh your views. If you have a table view based application, have a look at NSFetchedResultsController. This helps you update the table automatically with appropriate animations. If you don't use table views, you have to implement the UI update yourself.

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