Question

我搜索了很多并找到了很多解决方案，但没有一个能为我提供2012-12-31的正确周数。甚至MSDN上的示例（link）都失败了。

2012-12-31是星期一，因此它应该是第1周，但我尝试的每种方法都给了我53.以下是我尝试过的一些方法：

来自MDSN图书馆：

DateTimeFormatInfo dfi = DateTimeFormatInfo.CurrentInfo;
Calendar cal = dfi.Calendar;

return cal.GetWeekOfYear(date, dfi.CalendarWeekRule, dfi.FirstDayOfWeek);

解决方案2：

return new GregorianCalendar(GregorianCalendarTypes.Localized).GetWeekOfYear(date, CalendarWeekRule.FirstFourDayWeek, DayOfWeek.Monday);

解决方案3：

CultureInfo ciCurr = CultureInfo.CurrentCulture;
int weekNum = ciCurr.Calendar.GetWeekOfYear(dtPassed, CalendarWeekRule.FirstFourDayWeek, DayOfWeek.Monday);
return weekNum;

更新

当日期为2012-12-31时，以下方法实际返回1。换句话说，我的问题是我的方法没有遵循ISO-8601标准。

// This presumes that weeks start with Monday.
// Week 1 is the 1st week of the year with a Thursday in it.
public static int GetIso8601WeekOfYear(DateTime time)
{
    // Seriously cheat.  If its Monday, Tuesday or Wednesday, then it'll 
    // be the same week# as whatever Thursday, Friday or Saturday are,
    // and we always get those right
    DayOfWeek day = CultureInfo.InvariantCulture.Calendar.GetDayOfWeek(time);
    if (day >= DayOfWeek.Monday && day <= DayOfWeek.Wednesday)
    {
        time = time.AddDays(3);
    }

    // Return the week of our adjusted day
    return CultureInfo.InvariantCulture.Calendar.GetWeekOfYear(time, CalendarWeekRule.FirstFourDayWeek, DayOfWeek.Monday);
}

Answer 1

正如本MSDN page所述，ISO8601周和.Net周编号之间存在细微差别。

您可以参考MSDN博客中的这篇文章以获得更好的解释：“ISO 8601 Week of Year format in Microsoft .Net”

简单地说，.Net允许数周分开，而ISO标准则没有。在文章中还有一个简单的功能，可以获得一年中最后一周正确的ISO 8601周数。

更新以下方法实际上为2012-12-31返回1，这在ISO 8601中是正确的（例如德国）。

// This presumes that weeks start with Monday.
// Week 1 is the 1st week of the year with a Thursday in it.
public static int GetIso8601WeekOfYear(DateTime time)
{
    // Seriously cheat.  If its Monday, Tuesday or Wednesday, then it'll 
    // be the same week# as whatever Thursday, Friday or Saturday are,
    // and we always get those right
    DayOfWeek day = CultureInfo.InvariantCulture.Calendar.GetDayOfWeek(time);
    if (day >= DayOfWeek.Monday && day <= DayOfWeek.Wednesday)
    {
        time = time.AddDays(3);
    }

    // Return the week of our adjusted day
    return CultureInfo.InvariantCulture.Calendar.GetWeekOfYear(time, CalendarWeekRule.FirstFourDayWeek, DayOfWeek.Monday);
}

Answer 2

一年可能超过52周。每年有52个完整周+ 1或+2（闰年）额外。他们弥补了第53周。

52周* 7天= 364天。

因此，每年至少有一天额外的一天。两个闰年。这些额外的日子是否被视为自己的独立周？

确实需要几周的时间取决于您一周的开始日期。让我们考虑一下2012年。

美国（星期日 - >星期六）：2012-12-30周末为52周+短短2天。 2012-12-31。这导致总共53周。今年的最后两天（周日+周一）组成他们自己的短周。

检查您当前的文化设置，看看它在一周的第一天使用了什么。

正如你所看到的，结果是53是正常的。

欧洲（星期一 - 星期日）：1月2日（2012-1-2）是第一个星期一，所以这是第一周的第一天。询问1月1日的周数，你会得到52，因为它被视为2011年最后一周的一部分。

甚至可能有第54周。每隔28年发生1月1日和12月31日作为单独的星期。它也必须是闰年。

例如，2000年有54周。 1月1日（sat）是第一个星期的一天，12月31日（太阳）是第二个星期的一天。

var d = new DateTime(2012, 12, 31);
CultureInfo cul = CultureInfo.CurrentCulture;

var firstDayWeek = cul.Calendar.GetWeekOfYear(
    d,
    CalendarWeekRule.FirstDay,
    DayOfWeek.Monday);

int weekNum = cul.Calendar.GetWeekOfYear(
    d,
    CalendarWeekRule.FirstDay,
    DayOfWeek.Monday);

int year = weekNum == 52 && d.Month == 1 ? d.Year - 1 : d.Year;
Console.WriteLine("Year: {0} Week: {1}", year, weekNum);

打印出：年份：2012周：54

将上面例子中的CalendarWeekRule更改为FirstFullWeek或FirstFourDayWeek，然后你将返回53.让我们在星期一保持开始日，因为我们正在与德国打交道。

所以第53周开始于2012-12-31星期一，持续一天然后停止。

53是正确的答案。如果想尝试，请将文化改为德国。

CultureInfo cul = CultureInfo.GetCultureInfo("de-DE");

Answer 3

这是方式：

public int GetWeekNumber()
{
    CultureInfo ciCurr = CultureInfo.CurrentCulture;
    int weekNum = ciCurr.Calendar.GetWeekOfYear(DateTime.Now, CalendarWeekRule.FirstFourDayWeek, DayOfWeek.Monday);
    return weekNum;
}

最重要的是CalendarWeekRule参数。

见这里： https://msdn.microsoft.com/query/dev14.query?appId=Dev14IDEF1&l=IT-IT&k=k(System.Globalization.CalendarWeekRule);k(TargetFrameworkMoniker-.NETFramework

Answer 4

由于似乎没有.Net文化产生正确的ISO-8601周数，我宁愿完全绕过内置周确定，并手动进行计算，而不是尝试纠正部分正确的结果。

我最终得到的是以下扩展方法：

/// <summary>
/// Converts a date to a week number.
/// ISO 8601 week 1 is the week that contains the first Thursday that year.
/// </summary>
public static int ToIso8601Weeknumber(this DateTime date)
{
    var thursday = date.AddDays(3 - date.DayOfWeek.DayOffset());
    return (thursday.DayOfYear - 1) / 7 + 1;
}

/// <summary>
/// Converts a week number to a date.
/// Note: Week 1 of a year may start in the previous year.
/// ISO 8601 week 1 is the week that contains the first Thursday that year, so
/// if December 28 is a Monday, December 31 is a Thursday,
/// and week 1 starts January 4.
/// If December 28 is a later day in the week, week 1 starts earlier.
/// If December 28 is a Sunday, it is in the same week as Thursday January 1.
/// </summary>
public static DateTime FromIso8601Weeknumber(int weekNumber, int? year = null, DayOfWeek day = DayOfWeek.Monday)
{
    var dec28 = new DateTime((year ?? DateTime.Today.Year) - 1, 12, 28);
    var monday = dec28.AddDays(7 * weekNumber - dec28.DayOfWeek.DayOffset());
    return monday.AddDays(day.DayOffset());
}

/// <summary>
/// Iso8601 weeks start on Monday. This returns 0 for Monday.
/// </summary>
private static int DayOffset(this DayOfWeek weekDay)
{
    return ((int)weekDay + 6) % 7;
}

首先，((int)date.DayOfWeek + 6) % 7)确定工作日编号，0 =星期一，6 =星期日。

date.AddDays(-((int)date.DayOfWeek + 6) % 7)确定所请求周数之前的星期一的日期。

三天后是星期四的目标，它决定了一周中的哪一年。

如果您将年内的（从零开始）日期数除以7（向下舍入），您将获得该年度的（零基础）周数。

在c＃中，整数计算结果是隐式舍入的。

Answer 5

在.NET 3.0及更高版本中，您可以使用ISOWeek.GetWeekOfDate-Method。

请注意，年+周数字格式中的年份可能与DateTime的年份有所不同，因为周跨越了年份边界。

Answer 6

好消息！将pull request添加到{1}}到.NET Core刚刚合并，目前定于3.0版本。希望它能在不久的将来传播到其他.NET平台。

该类型具有以下签名，该签名应涵盖大多数ISO week需求：

System.Globalization.ISOWeek

您可以找到源代码here。

Answer 7

来自 il_guru 上面代码的Powershell端口的C＃：

About to call a generated method: I am a generated method

Answer 8

使用c＃和DateTime类确定周数ISO 8601样式的最简单方法。

问这个：今年星期四的星期四是星期四。答案等于想要的周数。

var dayOfWeek = (int)moment.DayOfWeek;
// Make monday the first day of the week
if (--dayOfWeek < 0)
    dayOfWeek = 6;
// The whole nr of weeks before this thursday plus one is the week number
var weekNumber = (moment.AddDays(3 - dayOfWeek).DayOfYear - 1) / 7 + 1;

Answer 9

var cultureInfo = CultureInfo.CurrentCulture;
var calendar = cultureInfo.Calendar;

var calendarWeekRule = cultureInfo.DateTimeFormat.CalendarWeekRule;
var firstDayOfWeek = cultureInfo.DateTimeFormat.FirstDayOfWeek;
var lastDayOfWeek = cultureInfo.LCID == 1033 //En-us
                    ? DayOfWeek.Saturday
                    : DayOfWeek.Sunday;

var lastDayOfYear = new DateTime(date.Year, 12, 31);

var weekNumber = calendar.GetWeekOfYear(date, calendarWeekRule, firstDayOfWeek);

 //Check if this is the last week in the year and it doesn`t occupy the whole week
return weekNumber == 53 && lastDayOfYear.DayOfWeek != lastDayOfWeek 
       ? 1  
       : weekNumber;

它适用于美国和俄罗斯文化。 ISO 8601也是正确的，因为俄罗斯周从星期一开始。

Answer 10

在 PowerShell 7.x.y 中：如果您需要匹配的 WeekYear，您将需要以下两个代码行。

[System.Globalization.ISOWeek]::GetWeekOfYear((get-date))
[System.Globalization.ISOWeek]::GetYear((get-date))

Answer 11

如果您没有 .NET 5.0，请扩展 DateTime 类以包含周数。

import { createApi } from "unsplash-js"

Answer 12

假设我们的一周从星期一开始，这两种方法将有所帮助

/// <summary>
    /// Returns the weekId
    /// </summary>
    /// <param name="DateTimeReference"></param>
    /// <returns>Returns the current week id</returns>
    public static DateTime GetDateFromWeek(int WeekReference)
    {
        //365 leap
        int DaysOffset = 0;
        if (WeekReference > 1)
        {
            DaysOffset = 7;
            WeekReference = WeekReference - 1;
        }
        DateTime DT = new DateTime(DateTime.Now.Year, 1, 1);
        int CurrentYear = DT.Year;
        DateTime SelectedDateTime = DateTime.MinValue;

        while (CurrentYear == DT.Year)
        {
            int TheWeek = WeekReportData.GetWeekId(DT);
            if (TheWeek == WeekReference)
            {
                SelectedDateTime = DT;
                break;
            }
            DT = DT.AddDays(1.0D);
        }

        if (SelectedDateTime == DateTime.MinValue)
        {
            throw new Exception("Please check week");
        }

        return SelectedDateTime.AddDays(DaysOffset);
    }
/// <summary>
    /// Returns the weekId
    /// </summary>
    /// <param name="DateTimeReference"></param>
    /// <returns>Returns the current week id</returns>
    public static int GetWeekId(DateTime DateTimeReference)
    {
        CultureInfo ciCurr = CultureInfo.InvariantCulture;
        int weekNum = ciCurr.Calendar.GetWeekOfYear(DateTimeReference,
        CalendarWeekRule.FirstFullWeek, DayOfWeek.Monday);
        return weekNum;
    }

Answer 13

根据il_guru的回答，我根据自己的需要创建了该版本，该版本还返回了年份成分。

    /// <summary>
    /// This presumes that weeks start with Monday.
    /// Week 1 is the 1st week of the year with a Thursday in it.
    /// </summary>
    /// <param name="time">The date to calculate the weeknumber for.</param>
    /// <returns>The year and weeknumber</returns>
    /// <remarks>
    /// Based on Stack Overflow Answer: https://stackoverflow.com/a/11155102
    /// </remarks>
    public static (short year, byte week) GetIso8601WeekOfYear(DateTime time)
    {
        // Seriously cheat.  If its Monday, Tuesday or Wednesday, then it'll
        // be the same week# as whatever Thursday, Friday or Saturday are,
        // and we always get those right
        DayOfWeek day = CultureInfo.InvariantCulture.Calendar.GetDayOfWeek(time);
        if (day >= DayOfWeek.Monday && day <= DayOfWeek.Wednesday)
        {
            time = time.AddDays(3);
        }
        // Return the week of our adjusted day
        var week = (byte)CultureInfo.InvariantCulture.Calendar.GetWeekOfYear(time, CalendarWeekRule.FirstFourDayWeek, DayOfWeek.Monday);
        return ((short)(week >= 52 & time.Month == 1 ? time.Year - 1 : time.Year), week);
    }

Answer 14

这里是il_guru的答案的扩展版本和可为空的版本。

扩展名：

public static int GetIso8601WeekOfYear(this DateTime time)
{
    var day = CultureInfo.InvariantCulture.Calendar.GetDayOfWeek(time);
    if (day >= DayOfWeek.Monday && day <= DayOfWeek.Wednesday)
    {
        time = time.AddDays(3);
    }

    return CultureInfo.InvariantCulture.Calendar.GetWeekOfYear(time, CalendarWeekRule.FirstFourDayWeek, DayOfWeek.Monday);
}

可空：

public static int? GetIso8601WeekOfYear(this DateTime? time)
{
    return time?.GetIso8601WeekOfYear();
}

用法：

new DateTime(2019, 03, 15).GetIso8601WeekOfYear(); //returns 11
((DateTime?) new DateTime(2019, 03, 15)).GetIso8601WeekOfYear(); //returns 11
((DateTime?) null).GetIso8601WeekOfYear(); //returns null

Answer 15

  DateTimeFormatInfo dfi = DateTimeFormatInfo.CurrentInfo;
  DateTime date1 = new DateTime(2011, 1, 1);
  Calendar cal = dfi.Calendar;

  Console.WriteLine("{0:d}: Week {1} ({2})", date1, 
                    cal.GetWeekOfYear(date1, dfi.CalendarWeekRule, 
                                      dfi.FirstDayOfWeek),
                    cal.ToString().Substring(cal.ToString().LastIndexOf(".") + 1));

Answer 16

问题是：您如何定义一周是在2012年还是在2013年？我想，您的假设是，自2013年的6天以来，本周应标记为2013年的第一周。

不确定这是否是正确的方法。那个星期开始于2012年（12月31日星期一），所以它应该被标记为2012年的最后一周，因此它应该是2012年的第53周。2013年的第一周应该从星期一到7日开始。

现在，您可以使用星期几信息处理边缘周（一年中的第一周和最后一周）的特定情况。这一切都取决于你的逻辑。

Answer 17

如果是一年（52 x 7 = 364），则一年有52周和1天或2天。 2012-12-31将是53周，一周只有2天，因为2012年是一年。

Answer 18

public int GetWeekNumber()
{
   CultureInfo ciCurr = CultureInfo.CurrentCulture;
   int weekNum = ciCurr.Calendar.GetWeekOfYear(DateTime.Now, 
   CalendarWeekRule.FirstFourDayWeek, DayOfWeek.Monday);
   return weekNum;
}

获取给定日期的正确周数

18 个答案:

扩展名：

可空：

用法：