NSFetchedResultsControllerDelegate methods don't get called

I have this in my viewWillAppear method

[RPCoreData
 getFetchedControllerForCategoryDiscoverDelegate:self completion:^(NSFetchedResultsController *controller) {
     self.fetchedResultController = controller;
     self.fetchedResultController.delegate = self;
 }];

and this in my CoreData.m

+ (void)
getFetchedControllerForCategoryDiscoverDelegate:(id<NSFetchedResultsControllerDelegate>)delegate
                                     completion:(void (^)(NSFetchedResultsController *controller))
                                                    completion {
    [MagicalRecord saveWithBlock:^(NSManagedObjectContext *localContext) {
      NSFetchedResultsController *controller = [ItemData MR_fetchAllGroupedBy:@"category.id"
                                                                withPredicate:nil
                                                                     sortedBy:@"category.id"
                                                                    ascending:NO
                                                                     delegate:delegate
                                                                    inContext:localContext];
      completion(controller);
    }];
}