根据年月日换算是第几周

转载

mob604756f2dcb4 2017-01-16 11:16:00

DateTimeExtensions

http://stackoverflow.com/questions/2136487/calculate-week-of-month-in-net/2136549#2136549

public static class DateTimeExtensions
    {
        private static readonly GregorianCalendar gregorianCalendar = new GregorianCalendar();

        public static int GetWeekOfMonth(this DateTime time)
        {
            DateTime first = new DateTime(time.Year, time.Month, 1);
            return time.GetWeekOfYear() - first.GetWeekOfYear() + 1;
        }

        public static int GetWeekOfYear(this DateTime time)
        {
            return gregorianCalendar.GetWeekOfYear(time, CalendarWeekRule.FirstDay, DayOfWeek.Sunday);
        }
    }

GetWeekOfYear

https://msdn.microsoft.com/en-us/library/system.globalization.calendar.getweekofyear(v=vs.110).aspx

Returns the week of the year that includes the date in the specified DateTime value.

public virtual int GetWeekOfYear(
    DateTime time,
    CalendarWeekRule rule,
    DayOfWeek firstDayOfWeek
)

rule: Type: System.Globalization.CalendarWeekRule
An enumeration value that defines a calendar week.

firstDayOfWeek: Type: System.DayOfWeek
An enumeration value that represents the first day of the week.

CalendarWeekRule

FirstDay

Indicates that the first week of the year starts on the first day of the year and ends before the following designated first day of the week. The value is 0.

FirstFourDayWeek

Indicates that the first week of the year is the first week with four or more days before the designated first day of the week. The value is 2.

FirstFullWeek

Indicates that the first week of the year begins on the first occurrence of the designated first day of the week on or after the first day of the year. The value is 1.

根据年份，计算该年的最大周数

 public static class DateTimeExtensions
    {
        private static readonly GregorianCalendar gregorianCalendar = new GregorianCalendar();

        public static int GetWeekOfYear(this DateTime time)
        {
            return gregorianCalendar.GetWeekOfYear(time, CalendarWeekRule.FirstFourDayWeek, DayOfWeek.Monday);
        }

        /// <summary>
        /// 根据年月日推算这一天属于哪一年的周
        /// 比如2017年01月01日,是2016年的第53周
        /// </summary>
        /// <param name="time"></param>
        /// <returns></returns>
        public static int GetYearOfWeek(this DateTime time)
        {
            int weeks = time.GetWeekOfYear();
            if (weeks == 53 && time.Month == 1)
            {
                return time.Year - 1;
            }
            return time.Year;
        }
    }

 for (int year = 1989; year <= 2017; year++)
                {
                    DateTime dateTime = new DateTime(year, 12, 31);
                    Console.WriteLine($"{dateTime.GetYearOfWeek()}年  最大周数={dateTime.GetWeekOfYear()}");
                }

2012年12月31日，是2012年的第53周，但是2011年没有第53周

1989年最大周数=52
1990年最大周数=53
1991年最大周数=53
1992年最大周数=53
1993年最大周数=52
1994年最大周数=52
1995年最大周数=52
1996年最大周数=53
1997年最大周数=53
1998年最大周数=53
1999年最大周数=52
2000年最大周数=52
2001年最大周数=53
2002年最大周数=53
2003年最大周数=53
2004年最大周数=53
2005年最大周数=52
2006年最大周数=52
2007年最大周数=53
2008年最大周数=53
2009年最大周数=53
2010年最大周数=52
2011年最大周数=52
2012年最大周数=53
2013年最大周数=53
2014年最大周数=53
2015年最大周数=53
2016年最大周数=52
2017年最大周数=52