asp.net 页面 输出之前修改 html（render）

protected override void Render(HtmlTextWriter writer)
{
    StringWriter output = new StringWriter();
    base.Render(new HtmlTextWriter(output));
    //This is the rendered HTML of your page. Feel free to manipulate it.
    string outputAsString = output.ToString();

    writer.Write(outputAsString);
}