public string SortDirection
        {
            get
            {
                string value = (string)ViewState["SortDirection"];
                return ((value == null) ? String.Empty : value);
            }
            set
            { ViewState["SortDirection"] = value; }
        }

        public string SortColumn
        {
            get
            {
                string value = (string)ViewState["SortColumn"];
                return ((value == null) ? String.Empty : value);
            }
            set
            { ViewState["SortColumn"] = value; }
        }