CoreData ascending:YES, show latest from the bottom - objective-c

Question

I have list of messages in my Core Data store(100 messages).
NSSortDescriptor * sortDescriptor = [[NSSortDescriptor alloc] initWithKey:#"created" ascending:YES];
NSArray *sortDescriptors = #[sortDescriptor];
[fetchRequest setSortDescriptors:sortDescriptors];
[fetchRequest setFetchLimit:20];
It shows only first 20 messages in the order I need.
What I need to do is: Show last 20 messages, sorted by date of creation, but they should appeared form the bottom of the TableView.
Storage:
1 : Test 1
2 : Test 2
3 : Test 3
It shows now as :
1 : Test 1
2 : Test 2
**Supposed to show in table View:**
3 : Test 3
2 : Test 2
1 : Test 1
fetchedResultsController:
- (NSFetchedResultsController *)fetchedResultsController{
if (_fetchedResultsController != nil) {
return _fetchedResultsController;
}
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription entityForName:#"Messages" inManagedObjectContext:self.managedObjectContext];
[fetchRequest setEntity:entity];
[fetchRequest setFetchLimit:20];
NSSortDescriptor * sortDescriptor = [[NSSortDescriptor alloc] initWithKey:#"created" ascending:YES];
NSArray *sortDescriptors = #[sortDescriptor];
[fetchRequest setSortDescriptors:sortDescriptors];
NSPredicate *predicate = [NSPredicate predicateWithFormat:#"(owner = %#) and (stream == %#) and (topic == %#)", ownerGuid,openStream,currentTopic];
[fetchRequest setPredicate:predicate];
NSFetchedResultsController *aFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:self.managedObjectContext sectionNameKeyPath:nil cacheName:nil];
aFetchedResultsController.delegate = self;
self.fetchedResultsController = aFetchedResultsController;
self.fetchedResultsController.delegate = self;
NSError *error = nil;
if (![self.fetchedResultsController performFetch:&error]) {
NSLog(#"Unresolved error %#, %#", error, [error userInfo]);
abort();
}
[self.fetchedResultsController performFetch:NULL];
return _fetchedResultsController;
}

Answer 1

All you should need to do is change the sortDescriptor to use ascending:NO so that it will get the last 20 messages.
NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:#"created" ascending:NO];
Now, you've got the right messages, they're just backwards in your array. You can easily reverse an array using the following code.
NSArray *messages = [[[fetchedMessages] reverseObjectEnumerator] allObjects];
EDIT:
Since you using a NSFetchedResultsController this solution would require a lot of additional code to work.
The easiest solution I can think of would be implement a custom method for getting your objects out of a fetched results controller.
- (id)objectAtIndexPath:(NSIndexPath *)indexPath
{
NSInteger sectionCount = [self.tableView numberOfRowsInSection:indexPath.section];
NSInteger newRowIndex = sectionCount - indexPath.row - 1;
NSIndexPath *newIndexPath = [NSIndexPath indexPathForRow:newRowIndex inSection:indexPath.section];
return [self.fetchedResultsController objectAtIndexPath:newIndexPath];
}
Then just replace
[self.fetchedResultsController objectAtIndexPath:indexPath];
with
[self objectAtIndexPath:indexPath];

Answer 2

#Clever answer is working for me. I called only NSIndexPath (return newIndexPath). I did not override method of the objectAtIndexPath. I was replaced below method.
- (NSIndexPath *)objectNewIndexPath:(NSIndexPath *)indexPath {
NSInteger sectionCount = [self.tableView numberOfRowsInSection:indexPath.section];
NSInteger newRowIndex = sectionCount - indexPath.row - 1;
NSIndexPath *newIndexPath = [NSIndexPath indexPathForRow:newRowIndex inSection:indexPath.section];
return newIndexPath;
}
Then just replace
[self.fetchedResultsController objectAtIndexPath:[self objectNewIndexPath:indexPath];