Question

In my understanding, NSFetchedResultsController do the job of sync data from managed object context to a table view controller. What’s the role of the delegate here? I read the apple documentation and don’t get it. Please elaborate the issue concisely and to the point.

Answer 1

Well, the brief answer is that the delegate methods allow you to update the table view as appropriate when an action has been taken on a managed object in the NSFetchedResultsController (NSFRC).

For example, if you delete an object that’s in the NSFRC’s results then it can update the table by removing the appropriate row.

So…

• In controllerWillChangeContent: it is a good idea to tell your table view that you’re going to change it (so you should call beginUpdates: on it)

• controller:didChangeObject:atIndexPath:forChangeType is called when a managed object changes (added, removed, moved, etc). Update the table view as appropriate (e.g. by calling deleteRowsAtIndexPaths:withRowAnimation: if a managed object was deleted)

• controller:didChangeSection:atIndex:forChangeType is similar to the above, but for table view sections.

• controllerDidChangeContent is called when the changes are complete. Finish up in this method also call endUpdates: on your table view

Hope this helps somewhat.