C#根据日期DateTime和持续时间int找到日期

  protected DateTime GetFinish(DateTime start, int duration)
        {
            return start.AddDays(duration);
        }

        protected DateTime GetStart(DateTime finish, int duration)
        {
            return finish.AddDays(-duration);
        }

        protected int GetDuration(DateTime start, DateTime finish)
        {
            return (finish - start).Days;
        }