为什么HtmlTextWriter没有渲染datetime列？

Question

我一直在尝试将存储过程导出为Excel工作表，但是datetime类型的列不会在结果表中呈现 这是一个简化的代码示例

System.Web.UI.WebControls.DataGrid grid = new System.Web.UI.WebControls.DataGrid();
string fileName = "";

using (dbentities ctx = new dbentities())
{
    grid.DataSource = ctx.GetRecord().Select(x => new { x.RequestID, x.CreatedDate }).ToList();
    grid.DataBind();
    fileName = "";

    using (StreamWriter sw = new StreamWriter(HttpContext.Current.Server.MapPath(fileName)))
    {
        using (HtmlTextWriter hw = new HtmlTextWriter(sw))
        {
            grid.RenderControl(hw);
        }
    }
}