[C#基础] 得到指定周数的开始和结束日期

        得到指定周数的开始和结束日期#region 得到指定周数的开始和结束日期
        public struct WeekRange
        ...{
            public DateTime BeginDate, EndDate;
        }

        public static WeekRange GetWeekRange(int year, int weekNumber, CalendarWeekRule rule, DayOfWeek firstDayOfWeek)
        ...{
            if (weekNumber > GetWeeksInYear(year, rule, firstDayOfWeek))
                throw new Exception("Out of week number");

            Calendar calendar = CultureInfo.InvariantCulture.Calendar;
            DateTime firstDateOfYear = new DateTime(year, 1, 1);
            int dayOfWeekIndex4ThisYearFirstDate = (int)calendar.GetDayOfWeek(firstDateOfYear);
            int firstDayOfWeekIndex = (int)firstDayOfWeek;
            int lastDayOfWeekIndex = firstDayOfWeekIndex + 6;
            WeekRange weekRange;
            int addDays, days;
            //1月1日 + days = 周的最后一天
            if (dayOfWeekIndex4ThisYearFirstDate < firstDayOfWeekIndex)
                days = firstDayOfWeekIndex - dayOfWeekIndex4ThisYearFirstDate - 1;
            else
                days = lastDayOfWeekIndex - dayOfWeekIndex4ThisYearFirstDate;

            switch (rule)
            ...{
                case CalendarWeekRule.FirstDay:
                    if (weekNumber == 1)
                    ...{
                        weekRange.EndDate = firstDateOfYear.AddDays(days);
                        weekRange.BeginDate = weekRange.EndDate.AddDays(-6);
                    }
                    else
                    ...{
                        addDays = days + 1 + (weekNumber - 2) * 7;
                        weekRange.BeginDate = firstDateOfYear.AddDays(addDays);

                        weekRange.EndDate = weekRange.BeginDate.AddDays(6);
                    }
                    break;
                case CalendarWeekRule.FirstFourDayWeek:
                default:
                    if (days + 1 >= 4)
                    ...{
                        if (weekNumber == 1)
                        ...{
                            weekRange.EndDate = firstDateOfYear.AddDays(days);
                            weekRange.BeginDate = weekRange.EndDate.AddDays(-6);
                        }
                        else
                        ...{
                            addDays = days + 1 + (weekNumber - 2) * 7;
                            weekRange.BeginDate = firstDateOfYear.AddDays(addDays);

                            weekRange.EndDate = weekRange.BeginDate.AddDays(6);
                        }
                    }
                    else
                    ...{
                        addDays = days + 1 + (weekNumber - 1) * 7;
                        weekRange.BeginDate = firstDateOfYear.AddDays(addDays);

                        weekRange.EndDate = weekRange.BeginDate.AddDays(6);
                    }
                    break;
                case CalendarWeekRule.FirstFullWeek:
                    if (dayOfWeekIndex4ThisYearFirstDate == firstDayOfWeekIndex)
                        addDays = (weekNumber - 1) * 7;
                    else
                        addDays = days + 1 + (weekNumber - 1) * 7;
                    weekRange.BeginDate = firstDateOfYear.AddDays(addDays);
                    weekRange.EndDate = weekRange.BeginDate.AddDays(6);
                    break;
            }
            return weekRange;
        }

        public static WeekRange GetWeekRange(int year, int weekNumber)
        ...{
            return GetWeekRange(year, weekNumber, CalendarWeekRule.FirstDay, DayOfWeek.Sunday);
        }

        public static int GetWeeksInYear(int year, CalendarWeekRule rule, DayOfWeek firstDayOfWeek)
        ...{
            Calendar calendar = CultureInfo.InvariantCulture.Calendar;
            DateTime NextYearFirstDate = new DateTime(year + 1, 1, 1);
            DateTime ThisYearLastDate = NextYearFirstDate.AddDays(-1);
            int count = calendar.GetWeekOfYear(ThisYearLastDate, rule, firstDayOfWeek);
            if (NextYearFirstDate.DayOfWeek != firstDayOfWeek)
                count--;
            return count;
        }

        public static int GetWeeksInYear(int year)
        ...{
            return GetWeeksInYear(year, CalendarWeekRule.FirstDay, DayOfWeek.Sunday);
        }
        #endregion