Question

每次与服务器同步时，都会刷新CoreData对象的所有字段。

即使没有任何变化，我仍然会在代码中的其他地方收到NSManagedObjectContextObjectsDidChangeNotification。

这是预期的行为吗？
如何防止这种情况，只有在实际发生变化时才会收到通知？

当我在刷新对象后添加下面的代码时，事情就像我想要的那样。但是为什么CoreData不能对此进行排序呢？

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

Answer 1

是的，即使值未更改，托管对象上下文中仍会发生新的写入。因此，预计会NSManagedObjectContextObjectsDidChangeNotification被解雇。

考虑使用NSFetchedResultsController作为：

@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

//现在在您的档案中

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);
}

现在，由于我们已将self作为fetchedResultsController的代理联系起来，self需要符合NSFetchedResultsControllerDelegate协议。
您选择覆盖任何可选方法，最直接的是：
- (void)controllerDidChangeContent:(NSFetchedResultsController *)controller

只有当CoreData对象发生变化时才会收到通知？

1 个答案: