已某个时间单位（日月周年）来分割时间段

       public List<RunningRange> GetRangesByUnit(string unit, DateTime start, DateTime end)
        {
            //根据单位获取时间段的数组 unit:M,W,D
            List<RunningRange> list = new List<RunningRange>();
            //获取两个时间相差的天数

            if ((end - start).Seconds < 0)
            {
                return list;
            }
            //单位日
            if (unit == "D")
            {
                int days = (end - start).Days;
                for (int i = 0; i <= days; i++)
                {
                    RunningRange range = new RunningRange();
                    range.Start = start.AddDays(i);
                    range.End = range.Start.AddDays(1);
                    list.Add(range);
                }
            }

            //单位周
            if (unit == "W")
            {
                DateTime startWeek = start.AddDays(1 - Convert.ToInt32(start.DayOfWeek.ToString("d")));
                DateTime endWeek = end.AddDays(1 + (7 - Convert.ToInt32(end.DayOfWeek.ToString("d"))));
                int weeks = (endWeek - startWeek).Days / 7;
                for (int i = 0; i <= weeks; i++)
                {
                    RunningRange range = new RunningRange();
                    DateTime time = start.AddDays(6 * i);
                    range.Start = time.AddDays(1 - Convert.ToInt32(time.DayOfWeek.ToString("d")));
                    range.End = range.Start.AddDays(7);
                    list.Add(range);
                }
            }

            //单位月
            if (unit == "M")
            {
                DateTime startMonth = start.AddDays(1 - start.Day);
                DateTime endMonth = end.AddDays(DateTime.DaysInMonth(end.Year, end.Month) - end.Month);
                int days = (endMonth - startMonth).Days;
                int MonthDays = 0;
                while (true)
                {
                    DateTime tempdate = startMonth;
                    MonthDays = DateTime.DaysInMonth(tempdate.Year, tempdate.Month);
                    RunningRange range = new RunningRange();
                    range.Start = tempdate;
                    range.End = range.Start.AddDays(MonthDays);
                    list.Add(range);
                    days -= MonthDays;
                    if (days <= 0)
                    {
                        break;
                    }

                    startMonth = range.End;
                }
            }
            if (unit == "Y")
            {
                //获取时间的年的部分
                int year = start.Year;
                int yearend = end.Year;
                for (int i = 0; i <= (yearend - year); i++)
                {
                    RunningRange range = new RunningRange();
                    range.Start = new DateTime(year + i, 1, 1);
                    range.End = range.Start.AddYears(1);
                    list.Add(range);
                }
            }
            return list;
        }