How To Sort GridView Columns

public partial class GridView : System.Web.UI.Page
{
         SqlConnection Con = new SqlConnection(@"Server=yourservername;Database=pubs;uid=userid;password=pwd;");
         SqlDataAdapter da = new SqlDataAdapter();
         DataTable dt = new DataTable();

        protected void Page_Load(object sender, EventArgs e)
       {
                     gv.DataSource = GetData();
                     gv.DataBind();
       }
       public DataTable GetData()
      {
                da = new SqlDataAdapter("Select * from authors", Con);
                da.Fill(dt);
                return dt;
       }
        protected void gv_Sorting(object sender, GridViewSortEventArgs e)
       {
                string stExp = e.SortExpression;
                string stDir = string.Empty;
                 if (StDir == SortDirection.Ascending)
                {
                       StDir = SortDirection.Descending;
                       stDir= "DESC";
                 }
                 else
                 {
                      StDir = SortDirection.Ascending;
                      stDir="ASC";
                  }
                  DataTable dt = GetData();
                  DataView dv = new DataView(dt);
                 dv.Sort = e.SortExpression + " " + stDir;
                 gv.DataSource = dv;
                 gv.DataBind();
        }
       public SortDirection StDir
      {
             get
             {
                    if (ViewState["sortDirection"] == null)
                   {
                         ViewState["sortDirection"] = SortDirection.Ascending;
                    }return (SortDirection)ViewState["sortDirection"];
              }
              set
             {
                       ViewState["sortDirection"] = value;
             }
      }
}