在私有/后台队列上创建NSManagedObjectContext：怎么办？ [英] Creating a NSManagedObjectContext on a private/background queue: how to do?

问题描述

我很困惑如何在主线程以外的其他线程上创建 MOC 。

在文档中，可以读

这样做的后果是上下文假定默认所有者是
分配它的线程或队列 - 这是由调用其init方法的线程
决定的。因此，您不应该在一个线程上初始化
上下文，然后将其传递给不同的线程。

另一方面，我已经看到代码，其中辅助 MOC 是通过以下方式创建在主线程：

  NSManagedObjectContext * parentContext = [[NSManagedObjectContext alloc] initWithConcurrencyType：NSPrivateQueueConcurrencyType]; 
 
 [parentContext performBlockAndWait：^ {
 [parentContext setUndoManager：nil]; // no point in it supporting undo 
 [parentContext setPersistentStoreCoordinator：coordinator]; 
}]; 
  

那么，什么是创建辅助 MOC ？也许我应该准确地说，这个辅助 MOC 是项目的中心类的 @property （ AppDelegate ）。

解决方案

文档最多含糊不清。

在我的测试中，您不需要使用队列将 NSManagedObjectContext 附加到其父级或 NSPersistentStoreCoordinator 。

如果你正在做一个 NSConfinmentConcurrencyType

如果你正在做一个 NSPrivateQueueConcurrencyType

/ code>我在创建它的线程上设置父或协调器。它是限制或限制到私有队列的 NSManagedObjectContext 的用法。我定义的用法是执行抓取，删除对象等。配置 NSManagedObjectContext 不受限制。

这当然不在文档中，但是当访问 NSManagedObjectContext 错误地引起异常时，通过测试返回结果。

I am confused about how to create a MOC on other threads than the main thread.

On one hand, in the doc, one can read

A consequence of this is that a context assumes the default owner is the thread or queue that allocated it—this is determined by the thread that calls its init method. You should not, therefore, initialize a context on one thread then pass it to a different thread.

But on the other hand, I have seen code where an auxiliary MOC is created the following way, on the main thread:

    NSManagedObjectContext *parentContext = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSPrivateQueueConcurrencyType];

    [parentContext performBlockAndWait:^{
        [parentContext setUndoManager:nil]; // no point in it supporting undo
        [parentContext setPersistentStoreCoordinator:coordinator];
    }];

So, what is the good way to create an auxiliary MOC? Maybe I should precise that this auxiliary MOC is a @property of a central class of the project (AppDelegate for example).

解决方案

The docs are ambiguous at best.

In my testing, you do not need to use a queue to attach the NSManagedObjectContext to its parent or the NSPersistentStoreCoordinator.

If you are doing a NSConfinmentConcurrencyType I set the parent or coordinator on the thread that created it (since that is the thread that can use it).

If you are doing a NSPrivateQueueConcurrencyType I set the parent or coordinator on the thread that created it as well. It is the usage of the NSManagedObjectContext that is confined or restricted to the private queue. I define the usage as executing a fetch, deleting an object, etc. Configuring the NSManagedObjectContext is not restricted.

This of course is not in the documentation but the results were produced through testing back when accessing a NSManagedObjectContext incorrectly caused an exception.

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