want to grid view to excel

GVAS.Visible = false;
       Response.Clear();
       Response.Buffer = true;
      // Response.AddHeader("content-disposition", "attachment;filename=GridViewExport.doc");

     //  Response.ContentType = "application/vnd.ms-word ";
       Response.ContentType = "application/vnd.xls";
       Response.Charset = "";
       Response.AddHeader("content-disposition",
               "attachment;filename=MyList.xls");
       StringWriter sw = new StringWriter();
       HtmlTextWriter hw = new HtmlTextWriter(sw);
       GVAS.AllowPaging = false;
       GVAS.DataBind();
       GVAS.RenderControl(hw);
       Response.Output.Write(sw.ToString());
       Response.Flush();
       Response.End();