[原创]判断两个日期是否在同一周

支持自定义每周的第一天是星期几

    public static class DateTimeExtension
    {
        public const DayOfWeek TheFirstDayOfWeek = DayOfWeek.Monday;

        private static int GetDayOfWeek(this DateTime date, DayOfWeek theFirstDayOfWeek = TheFirstDayOfWeek)
        {
            return ((int) date.DayOfWeek - (int) theFirstDayOfWeek + 7) % 7;
        }

        public static bool IsInSameWeek(this DateTime firstDate, DateTime secondDate,
            DayOfWeek theFirstDayOfWeek = TheFirstDayOfWeek)
        {
            var daySpan = (secondDate.Date - firstDate.Date).TotalDays;
            if (daySpan >= 7d || daySpan <= -7d)
            {
                return false;
            }

            var fisrtDayOfWeek = firstDate.GetDayOfWeek(theFirstDayOfWeek);
            var secondDayOfWeek = secondDate.GetDayOfWeek(theFirstDayOfWeek);

            return (daySpan >= 0) ^ (fisrtDayOfWeek >= secondDayOfWeek);
        }

        public static bool IsLastWeek(this DateTime date, DayOfWeek theFirstDayOfWeek = TheFirstDayOfWeek)
        {
            return date.AddDays(7).IsInSameWeek(DateTime.Today, theFirstDayOfWeek);
        }

        public static bool IsThisWeek(this DateTime date, DayOfWeek theFirstDayOfWeek = TheFirstDayOfWeek)
        {
            return date.IsInSameWeek(DateTime.Today, theFirstDayOfWeek);
        }
    }

代码很简单，只有最后一个return的位操作可能需要解释下

^ 异或:

true^true = false

true^false = true

false^true = true

false^false =false

用在bool操作可以理解为左右两边只有一个成立则为true

最后那个相当于

return (daySpan >= 0) ? fisrtDateOfWeek < secondDateOfWeek : fisrtDateOfWeek >= secondDateOfWeek;