NSManagedObjectController沒有在從addsManagedObjectContext更改合併

Question

我想通過調用mergeChangesFromContextDidSaveNotification與CoreData NSFetchedResultsController通過調用addingManagedObjectContext到我的主managedObjectContext中的更改。像這樣：

- (void)addGoalViewController:(AddGoalViewController *)controller didFinishWithSave:(BOOL)save { 
    if (save) { 
     NSNotificationCenter *dnc = [NSNotificationCenter defaultCenter]; 
     [dnc addObserver:self 
       selector:@selector(addControllerContextDidSave:) 
        name:NSManagedObjectContextDidSaveNotification 
        object:addingManagedObjectContext]; 

     NSLog(@"Before save - addingManagedObjectContext - Number of registered objects: %d", [[addingManagedObjectContext registeredObjects] count]); 
     NSLog(@"Before save - addingManagedObjectContext - Number of inserted objects: %d", [[addingManagedObjectContext insertedObjects] count]); 
     NSLog(@"Before save - addingManagedObjectContext - Number of updated objects: %d", [[addingManagedObjectContext updatedObjects] count]); 
     NSLog(@"Before save - addingManagedObjectContext - Number of deleted objects: %d", [[addingManagedObjectContext deletedObjects] count]); 

     // Save the new object to the adding managed object context 
     NSError *error = nil; 
     if ([addingManagedObjectContext hasChanges] && [addingManagedObjectContext save:&error] == NO) { 
      // Update to handle the error appropriately. 
      NSLog(@"Unresolved error %@, %@", error, [error userInfo]); 
      exit(-1); // Fail 
     } 

     NSLog(@"After save - addingManagedObjectContext - Number of registered objects: %d", [[addingManagedObjectContext registeredObjects] count]); 
     NSLog(@"After save - addingManagedObjectContext - Number of inserted objects: %d", [[addingManagedObjectContext insertedObjects] count]); 
     NSLog(@"After save - addingManagedObjectContext - Number of updated objects: %d", [[addingManagedObjectContext updatedObjects] count]); 
     NSLog(@"After save - addingManagedObjectContext - Number of deleted objects: %d", [[addingManagedObjectContext deletedObjects] count]); 

     // Remove the adding context observer 
     [dnc removeObserver:self name:NSManagedObjectContextDidSaveNotification object:addingManagedObjectContext]; 
    } 
    // Reset the adding context back to its default state 
    [addingManagedObjectContext reset]; 

    // Release the adding managed object context. 
    self.addingManagedObjectContext = nil; 

    // Dismiss the add goal view to return to the main list 
    [self dismissModalViewControllerAnimated:YES]; 
} 

我正在關注CoreDataBooks示例當我嘗試合併更改但儘管它不起作用。這裏是我的合併代碼：

- (void)addControllerContextDidSave:(NSNotification *)saveNotification { 
    NSManagedObjectContext* context = [fetchedResultsController managedObjectContext]; 
    // Merging changes causes the fetched results controller to update its results 
    NSLog(@"Before merge - managedObjectContext - Number of registered objects: %d", [[context registeredObjects] count]); 
    NSLog(@"Before merge - managedObjectContext - Number of inserted objects: %d", [[context insertedObjects] count]); 
    NSLog(@"Before merge - managedObjectContext - Number of updated objects: %d", [[context updatedObjects] count]); 
    NSLog(@"Before merge - managedObjectContext - Number of deleted objects: %d", [[context deletedObjects] count]); 
    [context mergeChangesFromContextDidSaveNotification:saveNotification]; 
    NSLog(@"After merge - managedObjectContext - Number of registered objects: %d", [[context registeredObjects] count]); 
    NSLog(@"After merge - managedObjectContext - Number of inserted objects: %d", [[context insertedObjects] count]); 
    NSLog(@"After merge - managedObjectContext - Number of updated objects: %d", [[context updatedObjects] count]); 
    NSLog(@"After merge - managedObjectContext - Number of deleted objects: %d", [[context deletedObjects] count]); 
} 

不幸的是，它似乎並沒有被添加對象到我的主要管理對象的情況下，將其添加到我的addingManagedObjectContext但合併後，應該將它們合併到主管理對象上下文。但是，我的主管理對象上下文中的註冊對象數保持爲0.保存後，請參閱addingManagedObjectContext中的1個註冊對象。這應該是我的主要managedObjectContext，因爲我合併它，但它不是。它堅持在我的addsManagedObjectContext中。

我已經看過了蘋果類引用文件，從我讀它好像

Before save - addingManagedObjectContext - Number of registered objects: 1 
Before save - addingManagedObjectContext - Number of inserted objects: 1 
Before save - addingManagedObjectContext - Number of updated objects: 1 
Before save - addingManagedObjectContext - Number of deleted objects: 0 
Before merge - managedObjectContext - Number of registered objects: 0 
Before merge - managedObjectContext - Number of inserted objects: 0 
Before merge - managedObjectContext - Number of updated objects: 0 
Before merge - managedObjectContext - Number of deleted objects: 0 
After merge - managedObjectContext - Number of registered objects: 0 
After merge - managedObjectContext - Number of inserted objects: 0 
After merge - managedObjectContext - Number of updated objects: 0 
After merge - managedObjectContext - Number of deleted objects: 0 
After save - addingManagedObjectContext - Number of registered objects: 1 
After save - addingManagedObjectContext - Number of inserted objects: 0 
After save - addingManagedObjectContext - Number of updated objects: 0 
After save - addingManagedObjectContext - Number of deleted objects: 0 

正如你從這個輸出是該對象添加到addingManagedObjectContext看到，但它不合並該對象轉換爲主managedObjectContext。相反，該對象保留在addingManagedObjectContext中。從Apple Class Reference看來，這似乎不應該發生。相反，它應該將對象合併到managedObjectContext中。並且似乎沒有任何方法可以檢查mergeChangesFromContextDidSaveNotification錯誤。

Answer 1

我的理解是，NSFetchedResultsController應該自動更新和合並上下文中的數據。如果在保存第二個上下文之前，您的對象位於獲取結果控制器的上下文中，那麼應該正在監視這些更新。

- (void)controllerDidChangeContent:(NSFetchedResultsController *)controller 

根據蘋果的文檔：

通知的接收器獲取的成果控制器已完成一個或處理您可以通過設置控制器上的代表和實現該方法檢查了這一點自己由於添加，移除，移動或更新而導致的更多更改。

有關詳細信息：NSFetchedResultsControllerDelegate