Decrease indexPath by one

Question

I'm filling a TableView with CoreData.

Until now I was doing something like this:

        NSManagedObject *managedObject = [self.fetchedResultsController objectAtIndexPath:indexPath];

...to retrieve the object to fill the row.

Everything was working fine until I realized I have to manage the first row of the table as an exception because the first line will contain other content, not provided by CoreData.

Now my issue is how can I manipulate the indexPath to shift everything by one. I would like to do something like this:

// I know this is not going to work, just to give you an idea...
   NSManagedObject *managedObject = [self.fetchedResultsController objectAtIndexPath:indexPath-1];

but I cannot find the right syntax to manipulate the indexPath. Can anyone help me? Thx for your time!

Answer 1

In case we are talking about iOS UITableView index path there's much easier way:

NSIndexPath* newIndexPath = [NSIndexPath indexPathForRow:oldIndexPath.row+1 inSection:oldIndexPath.section];

Cheers... :)

Answer 2

If you're talking about a standard iOS UITableView, then your index path is an instance of NSIndexPath, and will have two entries: a section index and a row index. If I understand you right, you want to decrement the row index by 1 every time you go to fill a table view cell. (I'm assuming you only have one section, or don't care about the section index - if this is wrong, please edit your question.)

Basically what you need to do is construct a new NSIndexPath instance with your adjusted indices, then use that to query your fetched results controller. Something like this would work (untested):

NSUInteger indexes[2];
[indexPath getIndexes:indexes];
indexes[1]--;
NSIndexPath * adjustedIndexPath = [[NSIndexPath alloc] initWithIndexes:indexes
                                                                length:2];
NSManagedObject * managedObject = [self.fetchedResultsController
                                    objectAtIndexPath:adjustedIndexPath];

This basically does the following:

1. Pulls the existing indexes into a C array of NSUIntegers
2. Decrements the last index (at position 1 - the row index) by 1
3. Creates a new NSIndexPath with the adjusted indexes from the C array
4. Fetches the managed object using the new index path

Note again that this doesn't touch the section index at all, and so will adjust every cell in your table, regardless of whether it's in your first section. If that's not what you want, either wrap the adjustment in a conditional (e.g. if([indexPath indexAtPosition:0] == 0)) or add your own custom logic.