How can I edit a mutable property in Objective C?

Question

Hello.

I am trying to edit a mutable array from a property and can't seem to directly make it work. Consider the following code that seems to work, but seems also very inefficient; I have to copy the whole property array just to make a change in one object. Why can I change the whole "carNames" array, but can't make a change to one of it's objects?

Thank you for any light you might be able to provide...

// CarTableViewController.h


// ...


@interface CarTableViewController : UITableViewController {
    NSMutableArray *carNames;
}

@property (nonatomic, retain) NSMutableArray *carNames;

-(IBAction)addCarButton:(id)sender;
// ...
// --------------------------------------

// -------CarTableViewController.m-------

// ...
- (void)tableView:(UITableView *)tableView commitEditingStyle:(UITableViewCellEditingStyle)editingStyle forRowAtIndexPath:(NSIndexPath *)indexPath
{

    if (editingStyle == UITableViewCellEditingStyleDelete) {

     // Could I somehow run the removeOjectAtIndex: 
     // directly on the carNames Property?  - this code works...

     NSMutableArray *mutablecarNames = [carNames mutableCopy];
     [mutablecarNames removeObjectAtIndex:indexPath.row];
     carNames = [mutablecarNames copy];
     [mutablecarNames release];

            // This code doesn't work... Why?
            // [carNames removeObjectAtIndex:indexPath.row];

    }

// ...

Answer 1

You're setting carNames to be the result of [mutableCarNames copy], which is an immutable NSArray. You want mutableCopy instead.

Answer 2

Why are you not just calling [carNames removeObjectAtIndex:indexPath.row]?

That should work just fine, since it is a mutable array.