gridview export in excel

string datestyle = @"<style> .nf{mso-number-format:\@;}</style>";
        MainGridView.Visible = true;
        MainGridView.ForeColor = System.Drawing.Color.Black;
        MainGridView.AllowPaging = false;
         MainGridView.DataSource = Session["objListRechargeDTO"];
         MainGridView.DataBind();
        Response.Clear();
        Response.AddHeader("content-disposition", "attachment;filename=OneCardTransactionReport.xls");
        Response.Charset = "";
        Response.ContentType = "application/xls";
        System.IO.StringWriter WriteItem = new System.IO.StringWriter();
        System.Web.UI.HtmlTextWriter htmlText = new HtmlTextWriter(WriteItem);
        MainGridView.HeaderRow.Style.Add("background-color", "#CCCCCC");
        MainGridView.HeaderRow.Style.Add("background-color", "#CCCCCC");
       // MainGridView.Columns[2].Style.Add("Color","#000000");
        MainGridView.Columns[0].Visible = false;
        MainGridView.Columns[13].Visible = false;
        MainGridView.Columns[14].Visible = false;
        for (int i = 0; i < MainGridView.Rows.Count; i++)
        {
            HyperLink hl = (HyperLink)MainGridView.Rows[i].FindControl("hl");
            hl.NavigateUrl = "";
            HyperLink custemail = (HyperLink)MainGridView.Rows[i].FindControl("custemail");
            custemail.NavigateUrl = "";
        }
            Response.Write(datestyle);
        MainGridView.AllowPaging = false;
        MainGridView.RenderControl(htmlText);
        Response.Write(WriteItem.ToString());
        // Response.BinaryWrite((byte[])command.ExecuteScalar());
        Response.End();