C# 生成指定N位随机码

        /// <summary>
        /// 获取随机码
        /// </summary>
        /// <param name="length">长度</param>
        /// <param name="availableChars">指定随机字符，为空，默认系统指定</param>
        /// <returns></returns>
        private string GetRandomString(int length, string availableChars = null)
        {
            if (availableChars == null) availableChars = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";

            var id = new char[length];
            Random random = new Random();
            for (var i = ; i < length; i++)
            {
                id[i] = availableChars[random.Next(, availableChars.Length)];
            }

            return new string(id);
        }