public int GetItemSortedPosition(int index, object sender)
        {
            IComparer comparer = GetSortComparer();
            if (comparer == null)
                return index;
            if (_list.Count > 1)
                for (int i = 0; i < _list.Count; i++)
                    if (i != index && comparer.Compare(_list[i], sender) > 0)
                    {
                        if (i > 0 && i > index)
                            return i - 1;
                        return i;
                    }
            return _list.Count - 1;
        }