C#正则表达式判断URL是否正确

        /// <summary>
        /// C#正则表达式判断URL是否正确
        /// </summary>
        /// <param name="url"></param>
        /// <returns></returns>
        private bool IsUrl(string url)
        {
            var express = @"^(https?|ftp|file|ws)://([\w-]+\.)+[\w-]+(/[\w- ./?%&=]*)?$";
            Regex r = new Regex(express);
            var b = r.IsMatch(url);
            return b;
        }