有时候需要计算今天是第几周,以及本周从哪天开始:
/// <summary> /// 根据第几周和星期几获取具体的某天的日期 /// </summary> /// <param name="year"></param> /// <param name="week">第几周</param> /// <param name="day">周几(1、2、3、4、5、6、7)</param> /// <returns>返回指定的日期</returns> public static DateTime GetTimeByWeek(int? year, int? week, int? day) { if (year == null) year = 2019; if (week == null) week = 1; if (day == null) day = 1; DateTime dt = Convert.ToDateTime(year + "-1-1"); int i = dt.DayOfWeek - DayOfWeek.Monday; if (i == -1) i = 6; TimeSpan ts = new TimeSpan(i, 0, 0, 0); dt = dt.Subtract(ts).AddDays((week.Value - 1)*7);//获取周一 dt = dt.AddDays(day.Value - 1);//获取指定的某天 return dt; } /// <summary> /// 根据日期获取第几周 /// </summary> /// <param name="dtime"></param> /// <returns></returns> public static int GetWeekByTime(DateTime dtime) { //确定此时间在一年中的位置 int dayOfYear = dtime.DayOfYear; //当年第一天 DateTime tempDate = new DateTime(dtime.Year, 1, 1); //确定当年第一天 int tempDayOfWeek = (int)tempDate.DayOfWeek; tempDayOfWeek = tempDayOfWeek == 0 ? 7 : tempDayOfWeek; //确定星期几 int index = (int)dtime.DayOfWeek; index = index == 0 ? 7 : index; //当前周的范围 DateTime retStartDay = dtime.AddDays(-(index - 1)); DateTime retEndDay = dtime.AddDays(6 - index); //确定当前是第几周 int weekIndex = (int)Math.Ceiling(((double)dayOfYear + tempDayOfWeek - 1) / 7); if (retStartDay.Year < retEndDay.Year) { weekIndex = 1; } return weekIndex; } /// <summary> /// 求某年有多少周 /// </summary> /// <param name="dtime"></param> /// <returns></returns> public static int GetWeeksOfYear(DateTime dtime) { int countDay = DateTime.Parse(dtime.Year + "-12-31").DayOfYear; int countWeek = countDay / 7; return countWeek; } /// <summary> /// 获取某月的第一天 /// </summary> /// <param name="dt"></param> /// <returns></returns> public static DateTime GetFirstDayOfMonth(DateTime dt) { return dt.AddDays(1 - dt.Day); } /// <summary> /// 获取某月的最后一天 /// </summary> /// <param name="dt"></param> /// <returns></returns> public static DateTime GetLastDayOfMonth(DateTime dt) { return dt.AddDays(1 - dt.Day).AddMonths(1).AddDays(-1); } /// <summary> /// 获取指定周起止时间描述 /// </summary> /// <param name="year"></param> /// <param name="week"></param> /// <returns></returns> public static string GetWeekStartToEndDay(int year,int week) { DateTime startTime = GetTimeByWeek(year,week,1); DateTime endTime = GetTimeByWeek(year, week, 7); return string.Format("{0:yyyy-MM-dd}~{1:yyyy-MM-dd}", startTime, endTime); }