CoreDataBooks Example - Reorder Cells? - iphone

Question

I am using the CoreDataBooks example code in my project and have implemented it nicely. I am attempting to add the ability to reorder the cells in the UITableView, however I am really struggling.
I have looked at a few techniques, the following seems the most logical and straightforward:
UITableView Core Data reordering
However, I can't get it working, the most suspicious thing being it includes a sort descriptor which might be conflicting with the sort descriptor implemented through the CoreDataBooks example, possible?
I can't pinpoint the problem.
Edit
- (NSFetchedResultsController *)fetchedResultsController {
if (fetchedResultsController != nil) {
return fetchedResultsController;
}
// Create and configure a fetch request with the Book entity.
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription entityForName:#"GuestInfo" inManagedObjectContext:managedObjectContext];
[fetchRequest setEntity:entity];
// Create the sort descriptors array.
NSSortDescriptor *descriptor = [[NSSortDescriptor alloc] initWithKey:#"displayOrder" ascending:YES];
NSArray *sortDescriptors = [[NSArray alloc] descriptor, nil];
[fetchRequest setSortDescriptors:sortDescriptors];
// Create and initialize the fetch results controller.
NSFetchedResultsController *aFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:managedObjectContext sectionNameKeyPath:#"firstName" cacheName:#"Root"];
self.fetchedResultsController = aFetchedResultsController;
fetchedResultsController.delegate = self;
return fetchedResultsController;
}
- (void)viewWillAppear {
myTableViewData = [self getRowObjects];
[self.tableView reloadData];
}
In my viewDidLoad this happens:
NSError *error;
if (![[self fetchedResultsController] performFetch:&error]) {
// Update to handle the error appropriately.
NSLog(#"Unresolved error %#, %#", error, [error userInfo]);
exit(-1); // Fail
}
Does that call fetchedResultsController or throw an error if it doesn't exist? I can't see what else would cause the problem.