Question

I have a NSFetchedResultsController to get the data for an UITableView. During the creation of the NSFetchedResultsController I create a NSPredicate that filters the data with an external condition. What’s the proper way to refetch the data? Just nil’ing the my __fetchedResultsController and recreating it seems a little bit brutal.

Thanks!

Answer 1

As indicated in my comment above I figured it out. What you need to do is save a reference to the NSFetchRequest and manipulate that straight away when needed. As a second step, you need to tell your NSFetchedResultsController to fetch it’s data again.

I did this by adding two new methods to the default NSFetchedResultsController “stack”:

- (void)configureFetchRequest {  
    NSObject *myExternalDependency = …;

    if (!__fetchRequest) {
        __fetchRequest = [[NSFetchRequest alloc] init];
    }

    NSEntityDescription *entity = [NSEntityDescription entityForName:@"EntityName" inManagedObjectContext:self.managedObjectContext];
    [__fetchRequest setEntity:entity];

    NSPredicate *filter = [NSPredicate predicateWithFormat:@"someValue == %@", [myExternalDependency someProperty]];
    [__fetchRequest setPredicate:filter];
}

- (void)performFetch {
    NSError *error = nil;
    if (![self.fetchedResultsController performFetch:&error]) {
        NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
        abort();
    }
}

So what I basically do now is call these two methods on creation of __fetchedResultsController (which I do initialize using __fetchRequest, of course) and every time my external dependency changes. That’s it.