aspnet将gridview的数据导出到Excel，怎么样同时给某一个列增加一个公式，Excel的公式

Question

如题！
代码片段：
protected void GridView1_RowDataBound(object sender, GridViewRowEventArgs e)
    {
           }
protected void btnExport_Click(object sender, EventArgs e)
    {
        Response.Clear();
        Response.AddHeader("content-disposition", "attachment;filename=" + HttpUtility.UrlEncode          Response.Charset = "GB2312";
        Response.ContentType = "application/vnd.xls";
        System.IO.StringWriter stringWrite = new System.IO.StringWriter();
        System.Web.UI.HtmlTextWriter htmlWrite = new HtmlTextWriter(stringWrite);
        ExBindData(GridView1);
        GridView1.RenderControl(htmlWrite);
        Response.Write(stringWrite.ToString());
        Response.End();
    }
 //导出到Execl
    public override void VerifyRenderingInServerForm(Control control)
    {
        // Confirms that an HtmlForm control is rendered for
    }
求解在线等。