GridView Sorting

protected void GridView_OnSorting(object sender, GridViewSortEventArgs e)

    {

        DataTable dtSortTable = ViewState["CompanyData"] as DataTable;

        if (dtSortTable != null)

        {

            DataView dvSort = new DataView();

            dvSort = dtSortTable.DefaultView;

            //dtViewData is your data table - which in this case is loaded in teh function SearchControls

            string str = Convert.ToString(e.SortDirection);

            e.SortDirection = SortDirection.Ascending;

            ViewState.Add("SortCol", Convert.ToString(e.SortExpression));

            if (ViewState[e.SortExpression] != null)

            {

                if (Convert.ToString(ViewState[e.SortExpression]) == "Ascending")

                {

                    e.SortDirection = SortDirection.Descending;

                    ViewState[e.SortExpression] = "Desending";

                    dvSort.Sort = e.SortExpression + " DESC";

                }

                else

                {

                    e.SortDirection = SortDirection.Ascending;

                    ViewState[e.SortExpression] = "Ascending";

                    dvSort.Sort = e.SortExpression + " ASC";

                }

            }

            else

            {

                ViewState.Add(Convert.ToString(e.SortExpression), "Ascending");

                dvSort.Sort = e.SortExpression + " ASC";

            }

            GridView.DataSource = dvSort;

            GridView.DataBind();

        }

    }