僅當CoreData對象發生更改時纔會通知？

Question

每次我與我的服務器同步時，我刷新我的CoreData對象的所有字段。

即使沒有任何變化，我仍然會在我的代碼的其他地方收到NSManagedObjectContextObjectsDidChangeNotification。

• 這是預期的行爲嗎？
• 我該如何防止這種情況發生，並且只有在某些事情已經發生變化時纔會得到通知？

當我在刷新對象後添加下面的代碼時，事情就像我想要的那樣工作。但爲什麼CoreData不能解決這個問題？

if (object.changedValues.count == 0) 
{ 
    [object.managedObjectContext refreshObject:object mergeChanges:NO]; 
} 

Answer 1

• 是，即使值不會改變新寫道：在管理對象上下文仍在發生。因此，NSManagedObjectContextObjectsDidChangeNotification預計將被解僱。

考慮使用NSFetchedResultsController爲：

@interface CoreDataHelper : NSObject <NSFetchedResultsControllerDelegate> 

@property (nonatomic, readonly) NSManagedObjectContext *context; 

+ (instancetype)sharedInstance; 

@end 

@implementation 
@synthesize context = _context; 

+ (instancetype)sharedInstance{ 
    static dispatch_once_t once; 
    static CoreDataHelper *sharedInstance; 
    dispatch_once(&once, ^{ 
     sharedInstance = [self new]; 
    }); 
    return sharedInstance; 
} 

- (NSManagedObjectContext *)context{ 

    if (_context != nil) { 
     return _context; 
    } 

    NSPersistentStoreCoordinator *coordinator = [self persistentStoreCoordinator]; // you know what goes in PSC here, right? 
    if (!coordinator) { 
     NSLOG(@"Argh! coordinator == nil"); 
     return nil; 
    } 

    _context = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSPrivateQueueConcurrencyType]; 
    [_context setPersistentStoreCoordinator:coordinator]; 
    return _context; 
} 

- (void)controllerDidChangeContent:(NSFetchedResultsController *)controller{ 
/* 
This function will be invoked by the OS whenever a Managed Object changes. 
Keep in mind that this will be invoked on the Managed Object Context Queue. 
This is the place where your logic to be performed whenever a object changes needs to be. 
*/ 
} 

@end 

//現在在你的文件現在

NSFetchedResultsController *fetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:[CoreDataHelper sharedInstance].context sectionNameKeyPath:nil cacheName:nil]; 

fetchedResultsController.delegate = [CoreDataHelper sharedInstance]; 

NSError *error; 
if (![fetchedResultsController performFetch:&error]){ 
    NSLOG(@"fetch error %@", error); 
} 

，因爲我們已經迷上了self爲fetchedResultsController代表，self需要符合到NSFetchedResultsControllerDelegate協議。
您選擇覆蓋所有的可選方法，最直接的幸福：
- (void)controllerDidChangeContent:(NSFetchedResultsController *)controller