c# - .NET 是否给了我错误的 2008 年 12 月 29 日的周数？

Question

根据官方（公历）日历，2008 年 12 月 29 日的周数为 1，因为在第 52 周的最后一天（即 28/12）之后，一年中只剩下三天或更少的天数。有点奇怪，但是好的，规则就是规则。

所以根据这个日历，我们有 2008/2009 年的这些边界值

• 28/12 是第 52 周
• 29/12 是第 1 周
• 1/1 是第 1 周
• 8/1 是第 2 周

C# 提供了一个 GregorianCalendar 类，它有一个函数GetWeekOfYear(date, rule, firstDayOfWeek).

该参数rule是一个具有 3 个可能值的枚举：FirstDay, FirstFourWeekDay, FirstFullWeek. 根据我的理解，我应该FirstFourWeekDay遵循规则，但我尝试了所有这些以防万一。

最后一个参数通知应该将哪个工作日视为一周的第一天，根据该日历，它是星期一，所以星期一。

所以我启动了一个快速而肮脏的控制台应用程序来测试这个：

using System;
using System.Globalization;

namespace CalendarTest
{
    class Program
    {
        static void Main(string[] args)
        {
            var cal = new GregorianCalendar();
            var firstWeekDay = DayOfWeek.Monday;
            var twentyEighth = new DateTime(2008, 12, 28);
            var twentyNinth = new DateTime(2008, 12, 29);
            var firstJan = new DateTime(2009, 1, 1);
            var eightJan = new DateTime(2009, 1, 8);
            PrintWeekDays(cal, twentyEighth, firstWeekDay);
            PrintWeekDays(cal, twentyNinth, firstWeekDay);
            PrintWeekDays(cal, firstJan, firstWeekDay);
            PrintWeekDays(cal, eightJan, firstWeekDay);
            Console.ReadKey();
        }

        private static void PrintWeekDays(Calendar cal, DateTime dt, DayOfWeek firstWeekDay)
        {
            Console.WriteLine("Testing for " + dt.ToShortDateString());
            Console.WriteLine("--------------------------------------------");
            Console.Write(CalendarWeekRule.FirstDay.ToString() + "\t\t");
            Console.WriteLine(cal.GetWeekOfYear(dt, CalendarWeekRule.FirstDay, firstWeekDay));
            Console.Write(CalendarWeekRule.FirstFourDayWeek.ToString() + "\t");
            Console.WriteLine(cal.GetWeekOfYear(dt, CalendarWeekRule.FirstFourDayWeek, firstWeekDay));
            Console.Write(CalendarWeekRule.FirstFullWeek.ToString() + "\t\t");
            Console.WriteLine(cal.GetWeekOfYear(dt, CalendarWeekRule.FirstFullWeek, firstWeekDay));
            Console.WriteLine("--------------------------------------------");
        }
    }
}

...这就是我得到的

Testing for 28.12.2008
--------------------------------------------
FirstDay                52
FirstFourDayWeek        52
FirstFullWeek           51
--------------------------------------------
Testing for 29.12.2008
--------------------------------------------
FirstDay                53
FirstFourDayWeek        53
FirstFullWeek           52
--------------------------------------------
Testing for 01.01.2009
--------------------------------------------
FirstDay                1
FirstFourDayWeek        1
FirstFullWeek           52
--------------------------------------------
Testing for 08.01.2009
--------------------------------------------
FirstDay                2
FirstFourDayWeek        2
FirstFullWeek           1
--------------------------------------------

因此，正如我们所见，上述组合均不符合官方日历（如果您赶时间，请注意 29/12 永远不会成为第 1 周）。

我在这里做错了什么？也许我缺少一些明显的东西？（现在是周五，比利时的工作时间很晚，请多多包涵；））

编辑：也许我应该解释一下：我需要的是一个适用于任何年份的函数，返回与我链接的公历相同的结果。所以 2008 年没有特殊的解决方法。

Answer 1

本文深入探讨了该问题和可能的解决方法。问题的中心是 .NET 日历实现似乎没有忠实地实现 ISO 标准

Answer 2

@Conrad 是正确的。DateTime 和 GregorianCalendar 的 .NET 实现不实现/遵循完整的 ISO 8601 规范。话虽如此，他们的规范非常详细，而且完全实现起来并不简单，至少在解析方面是这样。

以下网站提供了更多信息：

• http://www.iso.org/iso/en/prods-services/popstds/datesandtime.html
• http://www.w3.org/TR/NOTE-datetime
• http://www.cl.cam.ac.uk/~mgk25/iso-time.html
• http://www.cs.tut.fi/~jkorpela/iso8601.html
• http://hydracen.com/dx/iso8601.htm
• http://www.probabilityof.com/ISO8601.shtml
• http://www.mcs.vuw.ac.nz/technical/software/SGML/doc/iso8601/ISO8601.html

简单的说：

一周由其在给定年份中的编号标识，并从星期一开始。一年的第一周是包括第一个星期四的那一周，或者相当于包括 1 月 4 日的那一周。

以下是我用于正确处理 ISO 8601 日期的部分代码：

    #region FirstWeekOfYear
    /// <summary>
    /// Gets the first week of the year.
    /// </summary>
    /// <param name="year">The year to retrieve the first week of.</param>
    /// <returns>A <see cref="DateTime"/>representing the start of the first
    /// week of the year.</returns>
    /// <remarks>
    /// Week 01 of a year is per definition the first week that has the Thursday 
    /// in this year, which is equivalent to the week that contains the fourth
    /// day of January. In other words, the first week of a new year is the week
    /// that has the majority of its days in the new year. Week 01 might also 
    /// contain days from the previous year and the week before week 01 of a year
    /// is the last week (52 or 53) of the previous year even if it contains days 
    /// from the new year.
    /// A week starts with Monday (day 1) and ends with Sunday (day 7). 
    /// </remarks>
    private static DateTime FirstWeekOfYear(int year)
    {
        int dayNumber;

        // Get the date that represents the fourth day of January for the given year.
        DateTime date = new DateTime(year, 1, 4, 0, 0, 0, DateTimeKind.Utc);

        // A week starts with Monday (day 1) and ends with Sunday (day 7).
        // Since DayOfWeek.Sunday = 0, translate it to 7. All of the other values
        // are correct since DayOfWeek.Monday = 1.
        if (date.DayOfWeek == DayOfWeek.Sunday)
        {
            dayNumber = 7;
        }
        else
        {
            dayNumber = (int)date.DayOfWeek;
        }

        // Since the week starts with Monday, figure out what day that 
        // Monday falls on.
        return date.AddDays(1 - dayNumber);
    }

    #endregion

    #region GetIsoDate
    /// <summary>
    /// Gets the ISO date for the specified <see cref="DateTime"/>.
    /// </summary>
    /// <param name="date">The <see cref="DateTime"/> for which the ISO date
    /// should be calculated.</param>
    /// <returns>An <see cref="Int32"/> representing the ISO date.</returns>
    private static int GetIsoDate(DateTime date)
    {
        DateTime firstWeek;
        int year = date.Year;

        // If we are near the end of the year, then we need to calculate
        // what next year's first week should be.
        if (date >= new DateTime(year, 12, 29))
        {
            if (date == DateTime.MaxValue)
            {
                firstWeek = FirstWeekOfYear(year);
            }
            else
            {
                firstWeek = FirstWeekOfYear(year + 1);
            }

            // If the current date is less than next years first week, then
            // we are still in the last month of the current year; otherwise
            // change to next year.
            if (date < firstWeek)
            {
                firstWeek = FirstWeekOfYear(year);
            }
            else
            {
                year++;
            }
        }
        else
        {
            // We aren't near the end of the year, so make sure
            // we're not near the beginning.
            firstWeek = FirstWeekOfYear(year);

            // If the current date is less than the current years
            // first week, then we are in the last month of the
            // previous year.
            if (date < firstWeek)
            {
                if (date == DateTime.MinValue)
                {
                    firstWeek = FirstWeekOfYear(year);
                }
                else
                {
                    firstWeek = FirstWeekOfYear(--year);
                }
            }
        }

        // return the ISO date as a numeric value, so it makes it
        // easier to get the year and the week.
        return (year * 100) + ((date - firstWeek).Days / 7 + 1);
    }

    #endregion

    #region Week
    /// <summary>
    /// Gets the week component of the date represented by this instance.
    /// </summary>
    /// <value>The week, between 1 and 53.</value>
    public int Week
    {
        get
        {
            return this.isoDate % 100;
        }
    }
    #endregion

    #region Year
    /// <summary>
    /// Gets the year component of the date represented by this instance.
    /// </summary>
    /// <value>The year, between 1 and 9999.</value>
    public int Year
    {
        get
        {
            return this.isoDate / 100;
        }
    }
    #endregion

Answer 3

周数因国家/地区而异，如果我不是完全错误的话，应该取决于您的语言环境/区域设置。

编辑：维基百科支持我的模糊回忆，即这些数字因国家/地区而异：http ://en.wikipedia.org/wiki/Week_number#Week_number

我希望一个受人尊敬的框架能够遵守您在本地运行时中选择的 COUNTRY。

Answer 4

以我的经验，所展示的行为是典型的行为，将部分最后一周称为第 53 周。这可能是因为我对周数的所有重大曝光都与为报告目的计算日历年末有关，而 IRS（或您选择的税务机构）认为日历年将于 12 月 31 日结束，而不是一年中的最后一个完整周。

Answer 5

我知道这是一个旧帖子，但任何方式 noda time 似乎都能得到正确的结果..

Answer 6

作为一种解决方法，您可以说周数是 WeekNumber mod 52。我相信这适用于您描述的情况。

Answer 7

作为一种解决方法，为什么不使用FirstFourDayWeek但添加：

  if ( weekNumber > 52 )
    weekNumber = 1;