怎么把DataGrid导出成.txt文件并保存到客户端？

我用了以下代码：
Response.Clear();
  　　      Response.Buffer= true;
            Response.Charset="utf-8";　　
            Response.AppendHeader("Content-Disposition","attachment;filename=FileFlow.txt");
            Response.ContentEncoding=System.Text.Encoding.GetEncoding("utf-8");　　
            Response.ContentType = "application/ms-txt";
  
  　　      this.EnableViewState = false;　　
             oStringWriter = new ();
  　　      System.Web.UI.HtmlTextWriter oHtmlTextWriter = new System.Web.UI.HtmlTextWriter(oStringWriter);
            DataGrid4.RenderControl(oHtmlTextWriter);
            Response.Write(oStringWriter.ToString());
Response.End();
但是导出的txt文件里包含一大堆html代码。怎么解决啊？