protected void gvUsers_Sorting(object sender, GridViewSortEventArgs e)
        {
            // prop is null at this point, so the next line fails
            if (ListUsers.Count > 0)
            {
                string        orderby   = gvUsers.OrderBy;
                SortDirection direction = SortDirection.Ascending;
                if (orderby.ToLower().EndsWith("desc"))
                {
                    direction = SortDirection.Descending;
                    orderby   = orderby.Split(' ')[0];
                }

                List <Twitter.User> sortedList = null;
                if (orderby == Constants.GetVariableName(() => ListUsers[0].Index))
                {
                    if (direction == SortDirection.Ascending)
                    {
                        sortedList = ListUsers.OrderBy(x => x.Index).ToList();
                    }
                    else
                    {
                        sortedList = ListUsers.OrderByDescending(x => x.Index).ToList();
                    }
                }
                else if (orderby == Constants.GetVariableName(() => ListUsers[0].ScreenName))
                {
                    if (direction == SortDirection.Ascending)
                    {
                        sortedList = ListUsers.OrderBy(x => x.ScreenName).ToList();
                    }
                    else
                    {
                        sortedList = ListUsers.OrderByDescending(x => x.ScreenName).ToList();
                    }
                }
                else if (orderby == Constants.GetVariableName(() => ListUsers[0].ProfileImage))
                {
                    if (direction == SortDirection.Ascending)
                    {
                        sortedList = ListUsers.OrderBy(x => x.ProfileImage).ToList();
                    }
                    else
                    {
                        sortedList = ListUsers.OrderByDescending(x => x.ProfileImage).ToList();
                    }
                }
                else if (orderby == Constants.GetVariableName(() => ListUsers[0].UserId))
                {
                    if (direction == SortDirection.Ascending)
                    {
                        sortedList = ListUsers.OrderBy(x => x.UserId).ToList();
                    }
                    else
                    {
                        sortedList = ListUsers.OrderByDescending(x => x.UserId).ToList();
                    }
                }
                ListUsers = new BindingList <Twitter.User>(sortedList);
                BindData();
            }
        }