numberOfRowsInSection: method for core data and multiple sections

Question

I am trying to show a table view with 2 sections. The first section will always have 1 row and the second section will have as many rows as data points. I am using Core Da

Answer 1

The reason is that the fetched results controller (FRC) has only one section (section #0), which you want to be displayed in the second section (section #1) of the table view.

This is possible, but you have to map between FRC section numbers and table view section numbers, e.g.

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
    if (section == 0) {
        return 1;
    } else {
        NSUInteger frcSection = section - 1;
        id <NSFetchedResultsSectionInfo> sectionInfo = [[self.fetchedResultsController sections] objectAtIndex:frcSection];
        return [sectionInfo numberOfObjects];
    }
}

The same mapping is necessary in cellForRowAtIndexPath.

In the FRC delegate methods didChangeObject, didChangeSection you have to add 1 to the section number before calling the table view methods (e.g. insertRowsAtIndexPaths).

---

ADDED: configureCell should look like this:

- (void)configureCell:(UITableViewCell *)cell atIndexPath:(NSIndexPath *)indexPath
{
    if (indexPath.section == 0) {
        cell.textLabel.text = entityOne.name;  //entityOne object passed from previous VC
    } else {
        NSIndexPath *frcIndexPath = [NSIndexPath indexPathForRow:indexPath.row inSection:(indexPath.section - 1)];
        entityTwo = [self.fetchedResultsController objectAtIndexPath:frcIndexPath];
        cell.textLabel.text = entityTwo.name;
    }
}

and didChangeObject like this:

- (void)controller:(NSFetchedResultsController *)controller
   didChangeObject:(id)anObject
       atIndexPath:(NSIndexPath *)indexPath
     forChangeType:(NSFetchedResultsChangeType)type
      newIndexPath:(NSIndexPath *)newIndexPath
{
    UITableView *tableView = self.tableView;
    NSIndexPath *tvIndexPath = [NSIndexPath indexPathForRow:indexPath.row inSection:(indexPath.section + 1)];
    NSIndexPath *tvNewIndexPath = [NSIndexPath indexPathForRow:newIndexPath.row inSection:(newIndexPath.section + 1)];

    switch(type) {
        case NSFetchedResultsChangeInsert:
            [tableView insertRowsAtIndexPaths:@[tvNewIndexPath] withRowAnimation:UITableViewRowAnimationFade];
            break;

        case NSFetchedResultsChangeDelete:
            [tableView deleteRowsAtIndexPaths:@[tvIndexPath] withRowAnimation:UITableViewRowAnimationFade];
            break;

        case NSFetchedResultsChangeUpdate:
            [self configureCell:[tableView cellForRowAtIndexPath:tvIndexPath] atIndexPath:tvIndexPath];
            break;

        case NSFetchedResultsChangeMove:
            [tableView deleteRowsAtIndexPaths:@[tvIndexPath] withRowAnimation:UITableViewRowAnimationFade];
            [tableView insertRowsAtIndexPaths:@[tvNewIndexPath] withRowAnimation:UITableViewRowAnimationFade];
            break;
    }
}

You probably get the idea:

• When going from FRC index path to table view index path, add one to the section.
• When going from table view index path to FRC index path, subtract one from the section.