c#想对地址转绝对地址

public static bool IsFullUrl(String link)
        {
            if (string.IsNullOrEmpty(link))
            {
                return false;
            }
            link = link.Trim().ToLowerInvariant();
            return link.StartsWith("http://") || link.StartsWith("https://");
        }
        public static String FullUrl(String parentUrl, String link)
        {
            if (IsFullUrl(link))
            {
                return link;
            }
            Uri pu = new Uri(parentUrl);
            Uri cu = new Uri(pu, link);
            return cu.AbsoluteUri;
        }