一组十六进制的字符串每两个转成对应值的byte

/// <summary>
        /// 一组十六进制的字符串每两个转成对应值的byte，比如4142 会成 AB对应的byte列表
        /// </summary>
        /// <param name="hexString"></param>
        /// <returns></returns>
        static List<byte> HexStringToBytes(string hexString)
        {
            if (hexString.Length %  != ) return null;

            List<byte> result = new List<byte>();

            for (int i = ; i < hexString.Length; i = i + )
            {
                byte v = Convert.ToByte(hexString[i].ToString(), );
                v <<= ;
                v += Convert.ToByte(hexString[i + ].ToString(), );

                result.Add(v);
            }
            return result;
            //return result;
        }

 private string ByteToString(byte[] bytes)
        {
            StringBuilder sb = new StringBuilder();
            foreach (var temp in bytes)
            {
                sb.Append(temp.ToString("X2"));
            }
            return sb.ToString();
        }