Question

I am using MagicalRecord to help with core data operation.

I have a NSOperation subclass called OfflineRetrieveOperation. It retrieve the message from the server and save it.
the code is like this:

NSManagedObjectContext *context = [NSManagedObjectContext contextForCurrentThread];
Message *existMessage = [Message MessageWithMessageID:messageID inManagedObjectContext:context];

if (!existMessage) {
  Message *message = [Message insertMessageWithProperties:properties inManagedObjectContext:context];
}
[context save];

The notification receiver is initialized like this:

- (id)init
{
  self = [super init];

  if (self != nil) {
    [[NSNotificationCenter defaultCenter] addObserver:self 
                                             selector:@selector(contextDidSave:) 
                                                 name:NSManagedObjectContextDidSaveNotification 
                                               object:[NSManagedObjectContext defaultContext]];
    [self setContext:[NSManagedObjectContext context]];
  }
  return self;
}

the log:

-[NSManagedObjectContext(MagicalRecord) saveWithErrorHandler:](0x5906a0) Saving Context
-[NSManagedObjectContext(MagicalRecord) mergeChangesFromNotification:](0x37eab0) Merging changes to *** DEFAULT *** context *** on Main Thread ***

Everything seems work fine except I can’t receive the NSManagedObjectContextDidSaveNotification at all, so that I can’t know that I have already finish retrieving.

Answer 1

Your OfflineRetrieveOperation is probably creating its own NSManagedObjectContext. When you save that context it will fire the NSManagedObjectContextDidSaveNotification. However you have an observer that will only listen for a NSNotification being broadcast by the [NSManagedObjectContext defaultContext].

Change your observer to consume notifications from your OfflineRetrieveOperation internal NSManagedObjectContext instead of [NSManagedObjectContext defaultContext] and it should start receiving them.