NSOutlineView row indexes changes when expanding item

Say I have a NSTableView (for example, a) and a NSOutlineView (for example, b).

In the datasource of a I'm trying to get the parent item of all the selected items of b. In the row no. rowIndex of a I would like to have the rowIndexth selected item of b and I would like to concatenate this string to the name of the parent of this item. For example, a:

• 1 and 1.1
• 2

And b:

• 1
  • 1.1 (selected)
• 2 (selected)
• 3

This is - (id)tableView:(NSTableView *)aTableView objectValueForTableColumn:(NSTableColumn *)aTableColumn row:(NSInteger)rowIndex of a.

NSUInteger index = [[outlineView selectedRowIndexes] firstIndex];

for (NSUInteger i = 0, target = rowIndex; i < target; i++)
    index = [[outlineView selectedRowIndexes] indexGreaterThanIndex:index];

NSLog(@"%@", [outlineView [outlineView itemAtRow:index]]);

if([outlineView parentForItem:[outlineView itemAtRow:index]] != NULL) {
    return [NSString s开发者_Go百科tringWithFormat:@"%@ %@", [outlineView parentForItem:[outlineView itemAtRow:index]], [outlineView itemAtRow:index]]; 
} else {
    return [outlineView itemAtRow:index];
}

return NULL;

The problem is that when I expand an item [outlineView parentForItem:[outlineView itemAtRow:index]] returns always the last expanded item.

I am trying to have a list of selected items and their parents. When I expand an item, all items change their parent to last expanded item.

Am I doing something wrong?

Thank you in advance.

You can't use a simple integer to represent an index in a nested set of data, as you found out. Instead you need to use NSIndexPath. As the docs put it:

The NSIndexPath class represents the path to a specific node in a tree of nested array collections. This path is known as an index path.