C#如何生成唯一订单号

/// <summary>
  /// 生成唯一数
  /// </summary>
  public class uniquedata
  {
    private static object obj = new object();
    private static int guidint { get { return guid.newguid().gethashcode(); } }
    private static string guidintstr { get { return math.abs(guidint).tostring(); } }

    /// <summary>
    /// 生成
    /// </summary>
    /// <param name="mark">前缀</param>
    /// <param name="timetype">时间精确类型 1 日,2 时,3 分，4 秒(默认) </param>
    /// <param name="id">id 小于或等于0则随机生成id</param>
    /// <returns></returns>
    public static string gener(string mark, int timetype = 4, int id = 0)
    {
      lock (obj)
      {
        var number = mark;
        var ticks = (datetime.now.ticks - guidint).tostring();
        int fillcount = 0;//填充位数

        number += gettimestr(timetype, out fillcount);
        if (id > 0)
        {
          number += ticks.substring(ticks.length - (fillcount + 3)) + id.tostring().padleft(10, '0');
        }
        else
        {
          number += ticks.substring(ticks.length - (fillcount + 3)) + guidintstr.padleft(10, '0');
        }
        return number;
      }
    }

    /// <summary>
    /// 生成
    /// </summary>
    /// <param name="mark">前缀</param>
    /// <param name="timetype">时间精确类型 1 日,2 时,3 分，4 秒(默认)</param>
    /// <param name="id">id 小于或等于0则随机生成id</param>
    /// <returns></returns>
    public static string generlong(string mark, int timetype = 4, long id = 0)
    {
      lock (obj)
      {
        var number = mark;
        var ticks = (datetime.now.ticks - guidint).tostring();
        int fillcount = 0;//填充位数

        number += gettimestr(timetype, out fillcount);
        if (id > 0)
        {
          number += ticks.substring(ticks.length - fillcount) + id.tostring().padleft(19, '0');
        }
        else
        {
          number += guidintstr.padleft(10, '0') + ticks.substring(ticks.length - (9 + fillcount));
        }
        return number;
      }
    }

    /// <summary>
    /// 获取时间字符串
    /// </summary>
    /// <param name="timetype">时间精确类型 1 日,2 时,3 分，4 秒(默认)</param>
    /// <param name="fillcount">填充位数</param>
    /// <returns></returns>
    private static string gettimestr(int timetype, out int fillcount)
    {
      var time = datetime.now;
      if (timetype == 1)
      {
        fillcount = 6;
        return time.tostring("yyyymmdd");
      }
      else if (timetype == 2)
      {
        fillcount = 4;
        return time.tostring("yyyymmddhh");
      }
      else if (timetype == 3)
      {
        fillcount = 2;
        return time.tostring("yyyymmddhhmm");
      }
      else
      {
        fillcount = 0;
        return time.tostring("yyyymmddhhmmss");
      }
    }
  }