iOS: NSFetchedResultsController - Core Data - page 23

NSManagedObjectContext associated with the NSFetchedResultsController changes, the
NSFetchedResultsController checks to see whether any of the objects it is referencing
are impacted. Further, it also watches inserts to determine whether any
newly inserted objects should be included in what is being referenced. If any
changes occur, the NSFetchedResultsController notifies its delegate of the changes.
The delegate is normally its associated UITableView .
Standing Up an NSFetchedResultsController
The creation of a NSFetchedResultsController takes a number of steps and uses
several of the classes that we discussed in Chapter 1, Under the Hood of Core
Data , on page 1 .
RecipesV1/PPRecipes/PPRMasterViewController.m
- (NSFetchedResultsController *)fetchedResultsController
{
if (fetchedResultsController) return fetchedResultsController;
NSManagedObjectContext *moc = [self managedObjectContext];
NSFetchRequest *fetchRequest = nil;
fetchRequest = [NSFetchRequest fetchRequestWithEntityName:@ "Recipe" ];
NSSortDescriptor *sort = [[NSSortDescriptor alloc] initWithKey:@ "name"
ascending:YES];
[fetchRequest setSortDescriptors:[NSArray arrayWithObject:sort]];
NSFetchedResultsController *frc = nil;
frc = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest
managedObjectContext:moc
sectionNameKeyPath:nil
cacheName:@ "Master" ];
[self setFetchedResultsController:frc];
[[self fetchedResultsController] setDelegate:self];
NSError *error = nil;
ZAssert([[self fetchedResultsController] performFetch:&error],
@ "Unresolved error %@\n%@" , [error localizedDescription],
[error userInfo]);
return fetchedResultsController;
}
The NSFetchedResultsController is effectively a wrapper around an NSFetchRequest .
Therefore, we first need to construct the NSFetchRequest that will be used. In
this example, we are building an NSFetchRequest that retrieves all of the available
recipes. Further, we are going to sort the Recipe entities based on their name
attribute.