how to transfer the data from a gridview to an excel file

protected void Button1_Click(object sender, EventArgs e)
    {
        this.EnableViewState = false;    //in case error occurs add this along with EnableEventValidation="false" set in source
        Response.Clear();

        Response.Buffer = true;

        Response.AddHeader("content-disposition", "attachment;filename=exp.xls");

        Response.Charset = "";

        Response.ContentType = "application/vnd.ms-excel";

        StringWriter sw = new StringWriter();

        HtmlTextWriter ht = new HtmlTextWriter(sw);

        GridView1.AllowPaging = false;

        GridView1.DataBind();

        GridView1.RenderControl(ht);

        Response.Output.Write(sw.ToString());

        Response.Flush();

        Response.End();

    }
    public override void VerifyRenderingInServerForm(System.Web.UI.Control control)
    {

    }