将CSS类应用于Web窗体上的无效控件

我需要将CSS类应用于Web窗体上的无效控件。我想让它成为一个可复苏的班级。这就是我目前为止所拥有的:

public class Validation
{
    public static void ApplyInvalidClass(Page page, string className)
    {
        foreach (System.Web.UI.WebControls.BaseValidator bv in page.Validators)
        {
            if (!bv.IsValid)
            {
                Control ctrl = page.FindControl(bv.ControlToValidate);

                if (ctrl != null)
                {
                    if (ctrl is TextBox)
                    {
                        TextBox txt = ctrl as TextBox;
                        txt.CssClass = "invalid";
                    }

                    if (ctrl is DropDownList)
                    {
                        DropDownList ddl = ctrl as DropDownList;
                        ddl.CssClass = "invalid";
                    }

                    if (ctrl is CheckBox)
                    {
                        CheckBox cb = ctrl as CheckBox;
                        cb.CssClass = "invalid";
                    }

                    if (ctrl is HtmlGenericControl)
                    {
                        HtmlGenericControl html = ctrl as HtmlGenericControl;
                        html.Attributes.Add("class", className);
                    }
                }
            }
        }
    }

}

问题是我在.NET用户控件上调用它,我猜是因为我正在传入page,page.findcontrol(bv.controltovalidate)始终为空。

有更好的方法吗?