数据可以完整导出来，但是没有列的标头。急需解决！

 /// <summary>
    /// 数据导出
    /// </summary>
    /// <param name="sender"></param>
    /// <param name="e"></param>
    protected void Button1_Click(object sender, EventArgs e)
    {
        string fileName = "Case History Record";
        System.IO.StringWriter sw = new System.IO.StringWriter(); System.Web.UI.HtmlTextWriter hw = new System.Web.UI.HtmlTextWriter(sw);
        rpt_Mod.RenderControl(hw); Response.Clear(); Response.ContentType = "application/vnd.ms-excel";//这里设置是选择导出excel，还是word
        Response.Charset = "";          
        rpt_Mod.Page.EnableViewState = true;
        System.Globalization.CultureInfo myCItrad = new System.Globalization.CultureInfo("ZH-CN", true);
        Response.AppendHeader("Content-Disposition", "attachment;filename=" + fileName + ".xls");//这里是文件名称设置           
        Response.Write("<meta http-equiv=Content-Type content=\"text/html; charset=UTF-8\"><table><tr><td>");          
        Response.Write(sw.ToString());          
        Response.Write("</td></tr></table>");      
        Response.End();
    }