C# 根據年、月、周、星期獲得日期等

        /// <summary>         /// 取指定日期是一年中的第幾周         /// </summary>         /// <param name="dtime">給定的日期</param>         /// <returns>數字 一年中的第幾周</returns>         public static int WeekOfYear(DateTime dtime)        {            try            {                //確定此時間在一年中的位置                int dayOfYear = dtime.DayOfYear;                //當年第一天                DateTime tempDate = new DateTime(dtime.Year, 1, 1);                //確定當年第一天                int tempDayOfWeek = (int)tempDate.DayOfWeek;                tempDayOfWeek = tempDayOfWeek == 0 ? 7 : tempDayOfWeek;                ////確定星期幾                int index = (int)dtime.DayOfWeek;                index = index == 0 ? 7 : index;                //當前周的範圍                DateTime retStartDay = dtime.AddDays(-(index - 1));                DateTime retEndDay = dtime.AddDays(6 - index);                //確定當前是第幾周                int weekIndex = (int)Math.Ceiling(((double)dayOfYear + tempDayOfWeek - 1) / 7);                if (retStartDay.Year < retEndDay.Year)                {                    weekIndex = 1;                }                return weekIndex;            }            catch (Exception ex)            {                throw new Exception(ex.Message);            }        }        /// <summary>        /// 求某年有多少周        /// </summary>        /// <param name="dtime"></param>        /// <returns></returns>        public static int GetWeekOfYear(DateTime dtime)        {            int countDay = DateTime.Parse(dtime.Year + "-12-31").DayOfYear;            int countWeek = countDay / 7;            return countWeek;        }        //根據年月日獲得星期幾        public static string CaculateWeekDay(int month, int day)        {            string weekstr = string.Empty;            int year = DateTime.Now.Year;            //把一月和二月看成是上一年的十三月和十四月            if (month == 1) { month = 13; year--; }            if (month == 2) { month = 14; year--; }            int week = (day + 2 * month + 3 * (month + 1) / 5 + year + year / 4 - year / 100 + year / 400) % 7;            switch (week)            {                case 0: weekstr = "1"; break;                case 1: weekstr = "2"; break;                case 2: weekstr = "3"; break;                case 3: weekstr = "4"; break;                case 4: weekstr = "5"; break;                case 5: weekstr = "6"; break;                case 6: weekstr = "7"; break;            }            return weekstr;        }        /// <summary>        /// 根據2個時間段獲得相應的周數        /// </summary>        /// <param name="beginDate"></param>        /// <param name="endDate"></param>        /// <returns></returns>        public static int WeekOfDate(DateTime beginDate, DateTime endDate)        {            TimeSpan ts1 = new TimeSpan(beginDate.Ticks);            TimeSpan ts2 = new TimeSpan(endDate.Ticks);            TimeSpan ts = ts2.Subtract(ts1).Duration();            int weeks = ts.Days / 7;            //確定此時間在一年中的位置            int dayOfYear = beginDate.DayOfYear;            //當年第一天            DateTime tempDate = new DateTime(beginDate.Year, beginDate.Month, beginDate.Day);            //最後一天            DateTime tempendDate = new DateTime(endDate.Year, endDate.Month, endDate.Day);            int tempDayOfWeek = (int)tempDate.DayOfWeek;            tempDayOfWeek = tempDayOfWeek == 0 ? 7 : tempDayOfWeek;            ////確定星期幾            int startindex = (int)beginDate.DayOfWeek;            startindex = startindex == 0 ? 7 : startindex;            //當前周的範圍            DateTime retStartDay = beginDate.AddDays(-(startindex - 1));            DateTime retEndDay = beginDate.AddDays(7 - startindex);            //確定當前是第幾周            int weekIndex = (int)Math.Ceiling(((double)dayOfYear + tempDayOfWeek - 1) / 7);            return weeks;        }        /// <summary>        /// 根據起始時間，擷取第幾周        /// </summary>        /// <param name="dtime">目前時間</param>        /// <returns></returns>        public static int WeekOfTermDate(DateTime dtime)        {                      string datetime = "2011-3-1";            TimeSpan ts1 = new TimeSpan(dtime.Ticks);            TimeSpan ts2 = new TimeSpan(Convert.ToDateTime(datetime).Ticks);            TimeSpan ts = ts2.Subtract(ts1).Duration();            //確定此時間在一年中的位置            int dayOfYear = ts.Days;            //當年第一天            DateTime tempDate = new DateTime(Convert.ToDateTime(datetime).Year, Convert.ToDateTime(datetime).Month, Convert.ToDateTime(datetime).Day);                       int tempDayOfWeek = (int)tempDate.DayOfWeek;            tempDayOfWeek = tempDayOfWeek == 0 ? 7 : tempDayOfWeek;            ////確定星期幾            int index = (int)dtime.DayOfWeek;            index = index == 0 ? 7 : index;            //當前周的範圍            DateTime retStartDay = dtime.AddDays(-(index - 1));            DateTime retEndDay = dtime.AddDays(7 - index);            //確定當前是第幾周            int weekIndex = (int)Math.Ceiling(((double)dayOfYear + tempDayOfWeek) / 7);                      return weekIndex;        }        /// <summary>        /// 根據周，星期獲得具體年月日        /// </summary>        /// <param name="week">第幾周</param>        /// <param name="day">星期幾</param>        /// <returns></returns>        public static DateTime DateTimeByWeekAndDay(int week, int day)        {                       DateTime someTime = Convert.ToDateTime("2011-3-1");            int i = someTime.DayOfWeek - DayOfWeek.Monday;              if (i == -1) i = 6;// i值 > = 0 ，因為枚舉原因，Sunday排在最前，此時Sunday-Monday=-1，必須+7=6。            TimeSpan ts = new TimeSpan(i, 0, 0, 0);                      //擷取第N周的星期一            someTime = someTime.Subtract(ts).AddDays((week - 1) * 7);            //獲得星期幾            someTime = someTime.AddDays(day - 1);            return someTime;        }