我在谷歌上搜索了很多,找到了很多解决方案,但没有一个能告诉我2012-12-31的正确周数。即使是MSDN上的例子(链接)也失败了。

2012-12-31是星期一,所以应该是第一周,但是我尝试的每一种方法都给了我53。以下是我尝试过的一些方法:

从MDSN库:

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date为2012-12-31时,下面的方法实际返回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);
}

当前回答

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))

其他回答

假设我们的一周从周一开始,这两种方法会有帮助

/// <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;
    }

问题是:你如何定义一个星期是在2012年还是2013年? 我猜,你的假设是,因为一周中有6天是在2013年,所以这周应该被标记为2013年的第一周。

我不确定这样做对不对。 那一周开始于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53日。2013年的第一周应该从7号星期一开始。

现在,您可以使用星期几信息处理边缘周(一年中的第一个和最后一个星期)的特定情况。这完全取决于你的逻辑。

由于似乎没有. net文化可以产生正确的ISO-8601周数,因此我宁愿完全绕过内置的周数确定,并手动执行计算,而不是试图更正部分正确的结果。

我最终得到了以下扩展方法:

/// <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)决定工作日的数字,0=周一,6=周日。

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

三天后是目标星期四,这决定了一周是哪一年。

如果将一年中(以零为基数)的天数除以7(四舍五入),就会得到一年中(以零为基数)的周数。

在c#中,整数计算结果隐式向下舍入。

如果没有。net 5.0,扩展DateTime类以包含周数。

public static class Extension {
    public static int Week(this DateTime date) {
        var day = (int)CultureInfo.CurrentCulture.Calendar.GetDayOfWeek(date);
        return CultureInfo.CurrentCulture.Calendar.GetWeekOfYear(date.AddDays(4 - (day == 0 ? 7 : day)), CalendarWeekRule.FirstFourDayWeek, DayOfWeek.Monday);
    }
}

是这样的:

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。

在这里看到的: https://msdn.microsoft.com/query/dev14.query?appId=Dev14IDEF1&l=IT-IT&k=k (System.Globalization.CalendarWeekRule)、k (TargetFrameworkMoniker -.NETFramework