write data gridview to excel sheet......

protected void btnExcel_Click(object sender, ImageClickEventArgs e)
    {
        //export to excel
        Response.Clear();
        Response.AddHeader("content-disposition", "attachment;filename=FileName.xls");
        Response.Charset = "";

        // If you want the option to open the Excel file without saving then
        // comment out the line below
        // Response.Cache.SetCacheability(HttpCacheability.NoCache);
        Response.ContentType = "application/vnd.xls";
        System.IO.StringWriter stringWrite = new System.IO.StringWriter();
        System.Web.UI.HtmlTextWriter htmlWrite = new HtmlTextWriter(stringWrite);
       //GV is the ID of gridview
        GV.RenderControl(htmlWrite);
        Response.Write(stringWrite.ToString());
        Response.End();
    }