Question

In my code i want to create tableView with List sections. I use scheme like this one:

I use NSFetchResultController which i define in this way:

- (NSFetchedResultsController *)fetchedResultsController {

    if (_fetchedResultsController != nil) {
        return _fetchedResultsController;
    }
    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
    NSEntityDescription *entity = [NSEntityDescription
                               entityForName:@"Item" inManagedObjectContext:coreDataController.masterManagedObjectContext];
    [fetchRequest setEntity:entity];

    NSSortDescriptor *sort = [[NSSortDescriptor alloc]
                          initWithKey:@"addedAt" ascending:YES];
    [fetchRequest setSortDescriptors:[NSArray arrayWithObject:sort]];

    [fetchRequest setFetchBatchSize:20];

    NSPredicate *predicate = [NSPredicate predicateWithFormat:@"itemIsChecked = 1"];

    [fetchRequest setPredicate:predicate];
    [fetchRequest setResultType:NSDictionaryResultType];

    NSFetchedResultsController *theFetchedResultsController =
    [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest
                                    managedObjectContext:coreDataController.masterManagedObjectContext sectionNameKeyPath:@"toList.listName"
                                               cacheName:nil];
    self.fetchedResultsController = theFetchedResultsController;
    _fetchedResultsController.delegate = self;

    return _fetchedResultsController;
}

Now in cellForRowAtIndexPath: i want to get data form my fetchResultController, so i do this in way:

Item *item = [self.fetchedResultsController objectAtIndexPath:indexPath];

and then if i want to access one of the item’s field (for example itemText), it crash:

NSLog(@"item itemtext = %@", item.itemText);

with error:

-[NSKnownKeysDictionary1 itemText]: unrecognized selector sent to instance 0x1215fd90

What i do wrong in my code?

Answer 1

You have set

[fetchRequest setResultType:NSDictionaryResultType];

and therefore the fetched results controller returns NSDictionary objects, not Item objects. So your element

Item *item = [self.fetchedResultsController objectAtIndexPath:indexPath];

is a NSDictionary, not an Item. Since dictionaries do not have a itemText method, item.itemText crashes. You could retrieve the value from the dictionary with

NSDictionary *item = [self.fetchedResultsController objectAtIndexPath:indexPath];
NSLog(@"item itemtext = %@", [item objectForKey:@"itemText"]);

But if you don’t have a specific reason to set the result type to NSDictionaryResultType, you should just delete that line. Change tracking of the fetched results controller (i.e. automatic table view updates) do not work with resultType == NSDictionaryResultType.

Note also that if you have set a sectionNameKeyPath, then you must add a sort descriptor with the same key path “toList.listName” and use it as first sort descriptor for the fetch request.