NSManagedObjectContext没有看到更改（“hasChanges”始终为false） [英] NSManagedObjectContext does not see changes ("hasChanges" always false)

问题描述

我有我认为是一个非常简单的设置使用核心数据：一个 NSManagedObjectContext 和两个 NSFetchedResultsController 。该应用程序有自己的子类 NSManagedObject 。

我所做的是或多或少以下（伪代码/流）：

  1。创建NSFetchRequest 
  - >使用它NSFetchedResultsController 
（和附加一个NSFetchedResultsControllerDelegate）
 2.从商店获取对象
 3.创建另一个NSFetchRequest（在/ from /具有相同的上下文）
  - >使用它第二个NSFetchedResultsController 
 4.获取对象的子集
 5.通过
更改一个对象[[[secondFetchedResultsController fetchedObjects] objectAtIndex：0] 
 setWhateverSyncedProperty：differentValue] 
 6.保存NSManagedObjectContext（ - >无错误）
 7.重启app  - >更改丢失
  

我认为我在文档中读到的是a）第一个FetchedResultsController的委托应该得到一个 controller：didChangeObject：atIndexPath：forChangeType：newIndexPath：事件和b）NSManagedObjectContext将更改保存到持久存储。这不会发生。

我也希望 NSManagedObjectContext 可以看到即当我调用hasChanges时返回 YES 。它不是。这可能也是不保存任何东西到永久存储的原因：它认为没有更改。

奇怪的是，当我NSLog的上下文的内容我请参阅已更改对象。因此变化在内存中...

最后但并非最不重要：当调用

  [[self managedObjectContext] refreshObject：[[[self fetchedResultsController] fetchedObjects] objectAtIndex：2] mergeChanges：YES]; 
  

委托获取 didChangeObject -message！

我有一种感觉，这可能与 hasChanges 下的键值相关注释 ：//developer.apple.com/library/ios/#documentation/Cocoa/Reference/CoreDataFramework/Classes/NSManagedObjectContext_Class/NSManagedObjectContext.htmlrel =nofollow> NSManagedObjectContext类参考，但我不grok

顺便说一下，我的想法和/或提示非常感谢。我在iPhone模拟器和XCode 3.2.5。

解决方案

请确保您的属性 @dynamic ，而不是 @synthesize

I have what I thought is a very simple setup using core data: one NSManagedObjectContext and two NSFetchedResultsControllers. The app has its own subclass of NSManagedObject.

What I do is more or less the following (pseudo code/flow):

1. create an NSFetchRequest
    -> with it an NSFetchedResultsController
       (and attach an NSFetchedResultsControllerDelegate)
2. fetch the objects from the store
3. create another NSFetchRequest (in/from/with the same context)
    -> with it a second NSFetchedResultsController
4. fetch a subset of objects
5. change an object via
    [[[secondFetchedResultsController fetchedObjects] objectAtIndex:0]
            setWhateverSyncedProperty:differentValue]
6. save the NSManagedObjectContext (-> no error)
7. restart app -> changes lost

What I think I read in the documentation is that a) the first FetchedResultsController's delegate should get an controller:didChangeObject:atIndexPath:forChangeType:newIndexPath: event and b) the NSManagedObjectContext saved the changes to the persistent store. Nothing of this happens.

I would also expect the NSManagedObjectContext to "see" the changes just before the save, i.e. return YES when I call "hasChanges" on it. It does not. This probably also is the reason for not saving anything to the persistent store: it thinks there are no changes.

Strangely enough though, when I "NSLog" the Context's contents I see the changed object. So the change is in memory...

Last but not least: when calling

[[self managedObjectContext] refreshObject:[[[self fetchedResultsController] fetchedObjects] objectAtIndex:2] mergeChanges:YES];

the delegate gets the didChangeObject-message!

I have a feeling that this could be related to the "Key-Value relevant notes" under hasChanges in the NSManagedObjectContext Class Reference but I don't grok the concept, I guess.

Any ideas and/or hints are greatly appreciated.

By the way: I am in iPhone simulator and on XCode 3.2.5.

解决方案

It happened to me before. make sure your properties are @dynamic and not @synthesize

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