Core Data reordering in Multiple sections

Question

In the following code reordering of rows in UITableView only works in the first section. After reordering rows in sections other than the first ,when the view reappears the rows go back to their original order Ive googled to no avail. Can anyone please help me get reordering working in all sections?

- (void)tableView:(UITableView *)tableView moveRowAtIndexPath:(NSIndexPath *)sourceIndexPath toIndexPath:(NSIndexPath *)destinationIndexPath;   
    userDrivenDataModelChange = YES;   
    NSMutableArray *things = [[__fetchedResultsController fetchedObjects] mutableCopy];
    // Grab the item we're moving.
    NSManagedObject *thing = [[self fetchedResultsController] objectAtIndexPath:sourceIndexPath];  
    // Remove the object we're moving from the array.
    [things removeObject:thing];
    // Now re-insert it at the destination.
    [things insertObject:thing atIndex:[destinationIndexPath row]];
    // All of the objects are now in their correct order. Update each
    // object's displayOrder field by iterating through the array.
    int i = 0;
    for (NSManagedObject *mo in things)
    {
        [mo setValue:[NSNumber numberWithInt:i++] forKey:@"displayOrder1"];  
    }   
    [things release], things = nil;   
    [__managedObjectContext save:nil];
    userDrivenDataModelChange = NO;
}

- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
{
    return [[self.fetchedResultsController sections] count];  
}

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
    id <NSFetchedResultsSectionInfo> sectionInfo = [[self.fetchedResultsController sections] objectAtIndex:section];
    return [sectionInfo numberOfObjects];
}

- (NSFetchedResultsController *)fetchedResultsController
{
    if (__fetchedResultsController != nil)
    {
       return __fetchedResultsController;
    }
    // Edit the entity name as appropriate.
    NSManagedObjectContext *context = [self managedObjectContext];
     NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
     [fetchRequest setEntity:[NSEntityDescription entityForName:@"Client" inManagedObjectContext:context]];
    [fetchRequest setFetchBatchSize:20];  
    // Edit the sort key as appropriate.
    NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"displayOrder1" ascending:YES];
     NSSortDescriptor *sortDescriptor2 = [[NSSortDescriptor alloc] initWithKey:@"area" ascending:YES];
    NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:sortDescriptor2 ,sortDescriptor ,nil];
    [fetchRequest setSortDescriptors:sortDescriptors];
    [sortDescriptor release];
    [sortDescriptor2 release];
    NSFetchedResultsController *aFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:self.managedObjectContext sectionNameKeyPath:@"area" cacheName:@"Root"];
    aFetchedResultsController.delegate = self;
    self.fetchedResultsController = aFetchedResultsController;
    [aFetchedResultsController release];
    [fetchRequest release];
    [sortDescriptors release];
     NSError *error = nil;
     if (![self.fetchedResultsController performFetch:&error])
    {
         NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
         abort();
     }
    return __fetchedResultsController;
}   

- (void)controllerWillChangeContent:(NSFetchedResultsController *)controller
{
    sectionInsertCount = 0; 
    if (userDrivenDataModelChange)return; {
        [self.tableView beginUpdates];      
    }
}

- (void)controller:(NSFetchedResultsController *)controller didChangeSection:(id <NSFetchedResultsSectionInfo>)sectionInfo  
           atIndex:(NSUInteger)sectionIndex forChangeType:(NSFetchedResultsChangeType)type
{
    if (userDrivenDataModelChange)return;{
     switch(type)
        {
            case NSFetchedResultsChangeInsert:
                [self.tableView insertSections:[NSIndexSet indexSetWithIndex:sectionIndex] withRowAnimation:UITableViewRowAnimationFade];
                break;
            case NSFetchedResultsChangeDelete:
                [self.tableView deleteSections:[NSIndexSet indexSetWithIndex:sectionIndex] withRowAnimation:UITableViewRowAnimationFade];
                break;
        }
    }
}

- (void)controller:(NSFetchedResultsController *)controller didChangeObject:(id)anObject atIndexPath:(NSIndexPath *)indexPath forChangeType:(NSFetchedResultsChangeType)type newIndexPath:(NSIndexPath *)newIndexPath
{
    if (userDrivenDataModelChange)return; {
      UITableView *aTableView = self.tableView;
      switch(type)
        {           
            case NSFetchedResultsChangeInsert:
                [aTableView insertRowsAtIndexPaths:[NSArray arrayWithObject:newIndexPath] withRowAnimation:UITableViewRowAnimationFade];
                break;
            case NSFetchedResultsChangeDelete:
                [aTableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade];
                break;
            case NSFetchedResultsChangeUpdate:
                [self configureCell:[tableView cellForRowAtIndexPath:indexPath] atIndexPath:indexPath];
                break;
            case NSFetchedResultsChangeMove:
                [aTableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade];
                [aTableView insertRowsAtIndexPaths:[NSArray arrayWithObject:newIndexPath]withRowAnimation:UITableViewRowAnimationFade];
                break;
        }
    }
}

- (void)controllerDidChangeContent:(NSFetchedResultsController *)controller
    if (userDrivenDataModelChange) return;
    [self.tableView endUpdates];
}

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

Answer 1

Since your things array is a mutable copy of the fetched results controller's fetchedObjects, none of the manipulations you do to things has any result on fetchedObjects.

Only the manual change shows up because all that change occurs in the fetched results controller's didChange... methods.

Edit:

Your problem is here:

NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"displayOrder1" ascending:YES];
 NSSortDescriptor *sortDescriptor2 = [[NSSortDescriptor alloc] initWithKey:@"area" ascending:YES];
NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:sortDescriptor2 ,sortDescriptor ,nil];
[fetchRequest setSortDescriptors:sortDescriptors];
[sortDescriptor release];
[sortDescriptor2 release];
NSFetchedResultsController *aFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:self.managedObjectContext sectionNameKeyPath:@"area" cacheName:@"Root"];

From the NSFetchedResultsController docs:

sectionNameKeyPath ... If this key path is not the same as that specified by the first sort descriptor in fetchRequest, they must generate the same relative orderings. For example, the first sort descriptor in fetchRequest might specify the key for a persistent property; sectionNameKeyPath might specify a key for a transient property derived from the persistent property.

Your primary sort key is displayOrder but your sectionNameKeyPath is area and I doubt they produce the same sort order.

It is usually bad practice to put an interface function such as displayOrder into the data model. What happens if you have multiple tables, all with different orders? Unless the ordering is arbitrary and something that the app needs to persist, don't create the attribute.

Also, in two places in the code, you have this construct:

if (userDrivenDataModelChange)return;{
  //...
}

While syntactically legal, this is just an bug waiting to happen. If the statement is true, the method returns immediately. If false, the block executes. That is an ugly, ugly construction that is way to easy to misread. Plus, you are issuing a void return. The compiler will warn you about this and you should pay attention to it.

Answer 2

Re: "an explanation why it only works in the first section and not in the others"

Scenario:

Section 1

• objectA at indexPath.section = 0, indexPath.row = 0
• objectB at indexPath.section = 0, indexPath.row = 1
• objectC at indexPath.section = 0, indexPath.row = 2

Section 2

• objectAA at indexPath.section = 1, indexPath.row = 0
• objectBB at indexPath.section = 1, indexPath.row = 1
• objectCC at indexPath.section = 1, indexPath.row = 2

When you copy objects into mutable array, your are "loosing" indexPath.section and your array looks like:

• objectA at index 0
• objectB at index 1
• objectC at index 2
• objectAA at index 3
• objectBB at index 4
• objectCC at index 5

When you remove and insert an object in 1st section you insert it at indexPath.row from 0 to 2 into your array indexes from 0 to 2, which is correct so it works

When you remove and insert an object in 2nd section you still insert it at indexPath.row from 0 to 2 (but indexPath.section 1 already) but your array does not have a section. so it is again inserted at indexes from 0 to 2, instead of 3 to 5, so it does not sort correctly