Scroll to last UITableViewCell using scrollToRowAtIndexPath:atScrollPosition:animated using NSFetchedResultsControllerDelegate methods - iphone

Question

I am adding a new item to the bottom of a UITableView and after inserting the item, I want the UITableView to scroll to the very bottom to display the newly inserted item. New items are saved to Core Data and the UITableView is automatically updated using NSFetchedResultsController.
- (void)controller:(NSFetchedResultsController *)controller didChangeObject:(id)anObject
atIndexPath:(NSIndexPath *)indexPath
forChangeType:(NSFetchedResultsChangeType)type
newIndexPath:(NSIndexPath *)newIndexPath
{
switch (type) {
case NSFetchedResultsChangeInsert:
NSLog(#"*** controllerDidChangeObject - NSFetchedResultsChangeInsert");
[self.tableView insertRowsAtIndexPaths:[NSArray arrayWithObject:newIndexPath] withRowAnimation:UITableViewRowAnimationFade];
//THIS IS THE CODE THAT DOESN'T WORK
[self.tableView scrollToRowAtIndexPath:newIndexPath atScrollPosition:UITableViewScrollPositionBottom animated:YES];
break;
....
}
This leads to an out of bounds error, I can't seem to make it work. I can scroll to the second to last comment by adjusting the row of the index path, but I can't get to the very last item.
Basically, I'm adding a comment to a table of comments and after a comment is added, I want the table to scroll to the most recent comment.

Answer 1

You need to call endUpdates so that the tableView can calculate its new sections and rows. A simple case would look like this:
[self.tableView beginUpdates];
[self.tableView insertRowsAtIndexPaths:[NSArray arrayWithObject:insertedIndexPath] withRowAnimation:UITableViewRowAnimationFade];
[self.tableView endUpdates];
[self.tableView scrollToRowAtIndexPath:insertedIndexPath atScrollPosition:UITableViewScrollPositionBottom animated:YES];
As you use NSFetchedResultsController, it is a bit more complicated, as the calls do beginUpdates, insertRowsAtIndexPaths:withRowAnimation:, and endUpdates are typically in different delegate methods. What you could do then is
add a property insertedIndexPath to store the inserted index path
after the -insertRowsAtIndexPaths:withRowAnimation: call in -controller:didChangeObject:atIndexPath:, add
self.insertedIndexPath = insertedIndexPath;
after [self.tableView endUpdates] in -controllerDidChangeContent:, add
if (self.insertedIndexPath) {
[self.tableView scrollToRowAtIndexPath:self.insertedIndexPath atScrollPosition:UITableViewScrollPositionBottom animated:YES];
self.insertedIndexPath = nil;
}

Answer 2

See if this helps...
[self.tableView beginUpdates];
[self.tableView insertRowsAtIndexPaths:[NSArray arrayWithObject:newIndexPath] withRowAnimation:UITableViewRowAnimationFade];
[self.tableView endUpdates];
[self.tableView scrollToRowAtIndexPath:newIndexPath atScrollPosition:UITableViewScrollPositionBottom animated:YES];