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);

        }