Error message deleting the last row of a section using NSFetchedResultsController

Question

I've got an UITableView that uses an NSFetchedResultsController as it's data source. I use one of the fields for my sections. I enabled row deletion (using the swipe gesture). Works just fine.

The problem comes up when I delete the last row of a section. It does not crash on me but the console shows the following message:

CoreData: error: Serious application error. An exception was caught from the delegate of NSFetchedResultsController during a call to -controllerDidChangeContent:. Invalid update: invalid number of rows in section 0. The number of rows contained in an existing section after the update (1) must be equal to the number of rows contained in that section before the update (1), plus or minus the number of rows inserted or deleted from that section (0 inserted, 1 deleted) and plus or minus the number of rows moved into or out of that section (0 moved in, 0 moved out). with userInfo (null)

This is all pretty basic stuff:

- (void)controllerWillChangeContent:(NSFetchedResultsController *)controller {
    [[self tableView] beginUpdates];
}

- (void)controller:(NSFetchedResultsController *)controller didChangeObject:(id)anObject
       atIndexPath:(NSIndexPath *)indexPath forChangeType:(NSFetchedResultsChangeType)type
      newIndexPath:(NSIndexPath *)newIndexPath {
    UITableView *tableView = self.tableView;

    switch(type) {
        …
        case NSFetchedResultsChangeDelete:
            [tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath]
                             withRowAnimation:UITableViewRowAnimationFade];

            break;

        case NSFetchedResultsChangeUpdate:
            [tableView reloadRowsAtIndexPaths:@[indexPath] withRowAnimation:UITableViewRowAnimationAutomatic];
            [self configureCell:[tableView cellForRowAtIndexPath:indexPath]
                    atIndexPath:indexPath];
            break;
        …
    }
}

- (void)controllerDidChangeContent:(NSFetchedResultsController *)controller {
    [[self tableView] endUpdates];
}

- (void)tableView:(UITableView *)tableView commitEditingStyle:(UITableViewCellEditingStyle)editingStyle forRowAtIndexPath:(NSIndexPath *)indexPath {
    if (editingStyle == UITableViewCellEditingStyleDelete) {
        // Delete the row from the data source            
        FHClass *foo = [[self fetchedResultsController] objectAtIndexPath:indexPath];;
        [[self managedObjectContext] deleteObject:meal];
        [self saveContext];
    }  
}

If I check -numberOfRowsInSection: I see that the number is steadily decreasing when deleting rows. Even to the point where it says 0.

What did I miss? Any hints? Stupid mistake on my part? ;-)

Answer 1

You should implement controller:didChangeSection:atIndex:forChangeType: to deal with section changes and then request the table view to deleteSections:.