Comments on: Moving objects within an NSMutableArray

By: Uday

Uday — Fri, 12 Feb 2010 00:59:38 +0000

Still not showing up right. Basically, the checks for the source index row being smaller or greater than the destination index row are contained in both the ‘insertObject’ and ‘removeObjectAtIndex’ message statements, using the conditional operator ‘?’.

By: Uday

Uday — Thu, 11 Feb 2010 23:55:24 +0000

Hmm, that didn’t show up right. Retry:

[people insertObject:[people objectAtIndex:sourceIndexPath.row] atIndex:destinationIndexPath.row+(sourceIndexPath.rowdestinationIndexPath.row?1:0))];

By: Uday

Uday — Thu, 11 Feb 2010 23:53:13 +0000

@Alexander
You’re totally right, I posted an incomplete solution. Here is the code from one of my apps:

[array insertObject:[people objectAtIndex:sourceIndexPath.row] atIndex:destinationIndexPath.row+(sourceIndexPath.rowdestinationIndexPath.row?1:0))];

By: Alexander

Alexander — Thu, 11 Feb 2010 14:36:05 +0000

@Uday
Your solution has a problem when the “from” index is smaller than the “to” index. Here’s an example:

The array has the following content:
0 1 2 3 4 5 6

You want to move item at index 2 to index 5. The first line of your code will result in the following array content (the content of index 2 (2) will be inserted at index 5):
0 1 2 3 4 2 5 6

The second line of code will remove the element at 2+1 = 3, and now the array has the following content:
0 1 2 4 2 5 6

But this is wrong. You’ve deleted element 3 and the element 2 is now twice in the array.

Only if the “to” index is smaller than the “from” index, your solution would work.

By: Uday

Uday — Thu, 11 Feb 2010 11:06:13 +0000

Alternatively, you could this:

[array insertObject:[array objectAtIndex:sourceIndexPath.row] atIndex:destinationIndexPath.row];
[array removeObjectAtIndex:(sourceIndexPath.row+1)];

By: Alexander

Alexander — Wed, 10 Feb 2010 18:37:16 +0000

@Cédric Luthi
No, I haven’t filed this to Apple yet.

By: Cédric Luthi

Cédric Luthi — Wed, 10 Feb 2010 16:39:40 +0000

Thanks for sharing. This method should definitely be added to NSMutableArray. Have you filed a radar that we can dupe?

By: Mark

Mark — Sun, 06 Dec 2009 10:00:01 +0000

Cool! This is exactly what I was looking for. It’s weird that some obvious functionality like this is not in the Interface!