[C#]获取某年指定周的开始日期和结束日期的通用方法

/// <summary> /// 获取一年中指定的一周的开始日期和结束日期。开始日期遵循ISO 8601即星期一。 /// </summary> /// <remarks>Write by vrhero</remarks> /// <param name="year">年（1 到 9999）</param> /// <param name="weeks">周（1 到 53）</param> /// <param name="weekrule">确定首周的规则</param> /// <param name="first">当此方法返回时，则包含参数 year 和 weeks 指定的周的开始日期的 System.DateTime 值；如果失败，则为 System.DateTime.MinValue。如果参数 year 或 weeks 超出有效范围，则操作失败。该参数未经初始化即被传递。</param> /// <param name="last">当此方法返回时，则包含参数 year 和 weeks 指定的周的结束日期的 System.DateTime 值；如果失败，则为 System.DateTime.MinValue。如果参数 year 或 weeks 超出有效范围，则操作失败。该参数未经初始化即被传递。</param> /// <returns>成功返回 true，否则为 false。</returns> public static bool GetDaysOfWeeks(int year, int weeks, CalendarWeekRule weekrule, out DateTime first, out DateTime last) { //初始化 out 参数 first = DateTime.MinValue; last = DateTime.MinValue; //不用解释了吧... if (year < 1 | year > 9999) return false; //一年最多53周地球人都知道... if (weeks < 1 | weeks > 53) return false; //取当年首日为基准...为什么？容易得呗... DateTime firstCurr = new DateTime(year, 1, 1); //取下一年首日用于计算... DateTime firstNext = new DateTime(year + 1, 1, 1); //将当年首日星期几转换为数字...星期日特别处理...ISO 8601 标准... int dayOfWeekFirst = (int)firstCurr.DayOfWeek; if (dayOfWeekFirst == 0) dayOfWeekFirst = 7; //得到未经验证的周首日... first = firstCurr.AddDays((weeks - 1) * 7 - dayOfWeekFirst + 1); //周首日是上一年日期的情况... if (first.Year < year) { switch (weekrule) { case CalendarWeekRule.FirstDay: //不用解释了吧... first = firstCurr; break; case CalendarWeekRule.FirstFullWeek: //顺延一周... first = first.AddDays(7); break; case CalendarWeekRule.FirstFourDayWeek: //周首日距年首日不足4天则顺延一周... if (firstCurr.Subtract(first).Days > 3) { first = first.AddDays(7); } break; default: break; } } //得到未经验证的周末日... last = first.AddDays(7).AddSeconds(-1); switch (weekrule) { case CalendarWeekRule.FirstDay: //周末日是下一年日期的情况... if (last.Year > year) last = firstNext.AddSeconds(-1); else if (last.DayOfWeek != DayOfWeek.Monday) last = first.AddDays(7 - (int)first.DayOfWeek).AddSeconds(-1); break; case CalendarWeekRule.FirstFourDayWeek: //周末日距下一年首日不足4天则提前一周... if (last.Year > year && firstNext.Subtract(first).Days < 4) { first = first.AddDays(-7); last = last.AddDays(-7); } break; default: break; } return true; }