Question

I have a UITableView populated with a mutablearray that is read from NSUserDefaults. I want the user to be able to remove some of the items present. Below is the code specific to the editing method and here is the whole file: http://pastebin.com/LmZMWBN9

When I click “edit” and remove an item the application crashes and I get back:

Terminating app due to uncaught exception ‘NSInternalInconsistencyException’, reason: ‘-[__NSCFArray removeObjectAtIndex:]: mutating method sent to immutable object’

My specific question is, what am I doing incorrectly here?

 // Override to support editing the table view.
- (void)tableView:(UITableView *)tableView commitEditingStyle:    (UITableViewCellEditingStyle)editingStyle forRowAtIndexPath:(NSIndexPath *)indexPath
{
if (editingStyle == UITableViewCellEditingStyleDelete) {

    // edit list of names 
    if ([listOfNames count] >= 1) {
        [tableView beginUpdates];
        [tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade];
        [listOfNames removeObjectAtIndex:[indexPath row]];

       // write updated listofnames to nsuserdefaults
        NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];

         [[NSUserDefaults standardUserDefaults] setObject:listOfNames forKey:@"My Key"];

        [defaults synchronize];

        if ([listOfNames count] == 0) {
            [tableView insertRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade];
        }
        [tableView endUpdates];
    }


}   
else if (editingStyle == UITableViewCellEditingStyleInsert) {
    // Create a new instance of the appropriate class, insert it into the array, and add a new row to the table view
}   
}

Answer 1

Your listOfNames instance variable is immutable, therefore you can’t remove objects from it.

Change:

listOfNames = [[defaults objectForKey:@"My Key"] copy];

to

listOfNames = [[defaults objectForKey:@"My Key"] mutableCopy];

in your -viewWillAppear: and viewDidLoad methods.