获取 本周、本月、本年 的开始或结束时间

 
 public class DateTimeUtil
    {
        // 获取 本周、本月、本年 的开始或结束时间
        /// <summary>
        /// 获取开始时间
        /// </summary>
        /// <param name="TimeType">Week、Month、Year</param>
        /// <param name="NowTime">当前时间</param>
        /// <returns></returns>
        public static string GetStarTimetByType(string TimeType, DateTime NowTime)
        {
            switch (TimeType)
            {
                case "Week":
                    return NowTime.AddDays((7 - (int)NowTime.DayOfWeek) % 7 - 7 + 1).ToString("yyyy-MM-dd 00:00:00");
                case "Month":
                    return NowTime.AddDays(-NowTime.Day + 1).ToString("yyyy-MM-dd 00:00:00");
                case "Year":
                    return NowTime.AddDays(-NowTime.DayOfYear + 1).ToString("yyyy-MM-dd 00:00:00");
                default://出错啦！！！
                    throw new NotImplementedException();
            }
        }
        /// <summary>
        /// 获取结束时间
        /// </summary>
        /// <param name="TimeType">Week、Month、Year</param>
        /// <param name="NowTime">当前时间</param>
        /// <returns></returns>
        public static string GetEndTimeByType(string TimeType, DateTime NowTime)
        {
            switch (TimeType)
            {
                case "Week":
                    return NowTime.AddDays((7 - (int)NowTime.DayOfWeek) % 7).ToString("yyyy-MM-dd 23:59:59");
                case "Month":
                    return NowTime.AddDays(-NowTime.AddMonths(1).Day + 1).AddMonths(1).AddDays(-1).ToString("yyyy-MM-dd 23:59:59");
                case "Year":
                    return NowTime.AddDays(-NowTime.DayOfYear + 1).AddYears(1).AddDays(-1).ToString("yyyy-MM-dd 23:59:59");
                default://出错啦！！！
                    throw new NotImplementedException();
            }
        }
        /// <summary>
        /// 根据第几周 获取开始时间和结束时间
        /// </summary>
        /// <param name="week">第几周</param>
        /// <param name="month">当前时间的月份</param>
        /// <returns></returns>
        public static Tuple<DateTime, DateTime> GetWeeks(int? week, int? month)
        {
            DateTime dt = DateTime.Parse($"{DateTime.Now.Year}-{month.Value}-{DateTime.Now.Day}");
            string[] arrDate0 = new string[6];
            string[] arrDate1 = new string[6];
            //年
            int year = dt.Year;
            //月
            //当前月第一天
            DateTime weekStart = new DateTime(year, month.Value, 1);
            //该月的最后一天
            DateTime monEnd = weekStart.AddMonths(1).AddDays(-1);
            int i = 1;
            //当前月第一天是星期几
            int dayOfWeek = Convert.ToInt32(weekStart.DayOfWeek.ToString("d"));
            //该月第一周结束日期
            DateTime weekEnd = dayOfWeek == 0 ? weekStart : weekStart.AddDays(7 - dayOfWeek);
            string content = "";
            // content += "第" + i + "周起始日期： " + weekStart.ToShortDateString() + "   结束日期： " + weekEnd.ToShortDateString() + "\n";
            arrDate0[0] = weekStart.ToString("yyyy-MM-dd 00:00:00");
            arrDate1[0] = weekEnd.ToString("yyyy-MM-dd 23:59:59");
 
            //当日期小于或等于该月的最后一天
            while (weekEnd.AddDays(1) <= monEnd)
            {
                i++;
                //该周的开始时间
                weekStart = weekEnd.AddDays(1);
                //该周结束时间
                weekEnd = weekEnd.AddDays(7) > monEnd ? monEnd : weekEnd.AddDays(7);
                arrDate0[i - 1] = weekStart.ToString("yyyy-MM-dd 00:00:00");
                arrDate1[i - 1] = weekEnd.ToString("yyyy-MM-dd 23:59:59");
            }
            content += year + "年" + month + "月共有" + i + "周\n";
            return Tuple.Create(DateTime.Parse(arrDate0[week.Value]), DateTime.Parse(arrDate1[week.Value]));
        }
   }