在.NET中计算月份的周数

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

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

用法:

DateTime time = new DateTime(2010, 1, 25);
Console.WriteLine(time.GetWeekOfMonth());

输出:

5

GetWeekOfYear 根据你的需要。

没有直接的内置方法可以做到这一点,但它可以很容易地做到。以下是一种扩展方法,可用于轻松获取日期的基于年份的周数:

public static int GetWeekNumber(this DateTime date)
{
    return GetWeekNumber(date, CultureInfo.CurrentCulture);
}

public static int GetWeekNumber(this DateTime date, CultureInfo culture)
{
    return culture.Calendar.GetWeekOfYear(date,
        culture.DateTimeFormat.CalendarWeekRule,
        culture.DateTimeFormat.FirstDayOfWeek);
}

然后我们可以用它来计算基于月份的周数,就像 Jason shows . 文化友好型的版本可能如下所示:

public static int GetWeekNumberOfMonth(this DateTime date)
{
    return GetWeekNumberOfMonth(date, CultureInfo.CurrentCulture);
}

public static int GetWeekNumberOfMonth(this DateTime date, CultureInfo culture)
{
    return date.GetWeekNumber(culture)
         - new DateTime(date.Year, date.Month, 1).GetWeekNumber(culture)
         + 1; // Or skip +1 if you want the first week to be 0.
}

这个标题有误导性。问题其实是关于 日历周数

对于当月的周数,您可以使用:

VB:
    Function WeekNumber(TargetDate As Date) As Integer
        Return (TargetDate.Day - 1) \ 7 + 1
    End Function

C#:
    public int WeekNumber(DateTime TargetDate)
    {
        return (TargetDate.Day - 1) / 7 + 1;
    }

如此处所述: http://forums.asp.net/t/1268112.aspx

您可以使用:

public static int Iso8601WeekNumber(DateTime dt)
{
    return  CultureInfo.CurrentCulture.Calendar.GetWeekOfYear(dt, CalendarWeekRule.FirstFourDayWeek, DayOfWeek.Monday);
}

public static int GetWeekOfMonth(DateTime dt)
{    
        
    int weekOfYear = Iso8601WeekNumber(dt);
    int weekOfYearAtFirst = Iso8601WeekNumber(dt.AddDays(1 - dt.Day));
    
    if (dt.Month == 1)
    {
        //week of year == week of month in January unless
        //December wraps
        if (weekOfYearAtFirst > 6) 
        {
            return weekOfYear > 6 ? 1 : weekOfYear + 1;
        }
        else 
        {
            return weekOfYear;
        }
    }

    return weekOfYear - weekOfYearAtFirst + 1;
}

请注意,您的需求可能会有所不同,因为存在某些算法选择。也就是说,2月底的星期一到星期五也是3月的第一周,或者是什么标准定义了一个月的“第一”周?ISO 8601:2004没有给出“月份中的一周”的定义。

VB版本:

Public Shared Function GetWeekNumber(ByVal [date] As DateTime) As Integer
    Return GetWeekNumber([date], CultureInfo.CurrentCulture)
End Function

Public Shared Function GetWeekNumber(ByVal [date] As DateTime, ByVal culture As CultureInfo) As Integer
    Return culture.Calendar.GetWeekOfYear([date], culture.DateTimeFormat.CalendarWeekRule, culture.DateTimeFormat.FirstDayOfWeek)
End Function

Public Shared Function GetWeekNumberOfMonth(ByVal [date] As DateTime) As Integer
    Return GetWeekNumberOfMonth([date], CultureInfo.CurrentCulture)
End Function

Public Shared Function GetWeekNumberOfMonth(ByVal [date] As DateTime, ByVal culture As CultureInfo) As Integer
    Return GetWeekNumber([date], culture) - GetWeekNumber(New DateTime([date].Year, [date].Month, 1), culture) + 1
    ' Or skip +1 if you want the first week to be 0.
End Function

这是我的解决方案:

    static string GetWeekNumber()
    {

        var weekNumber = CultureInfo.CurrentCulture.Calendar.GetWeekOfYear(DateTime.Now, CalendarWeekRule.FirstFourDayWeek,
            DayOfWeek.Sunday) -
        CultureInfo.CurrentCulture.Calendar.GetWeekOfYear(DateTime.Now.AddDays(1 - DateTime.Now.Day),
            CalendarWeekRule.FirstFourDayWeek, DayOfWeek.Sunday) + 1;

        switch (weekNumber)
        {
            case 1 :
                return "First";
            case 2:
                return "Second";
            case 3:
                return "Third";
            default:
                return "Fourth";
        }
    }

如果您希望将前7天视为第一周,即使该月不是从周日开始,这里有一个简单的选项:

class Program
{
    static void Main(string[] args)
    {
        var dates = Enumerable.Range(0, 10)
            .Select(r => new DateTime(2015, 10, 1).AddDays(r))
            .Select(q => new { Date = q, WeekOfMonth = q.WeekOfMonth() });

        foreach(var item in dates)
        {
            Console.WriteLine("Date: {0:ddd MM-dd-yyyy}, WOM: {1}", item.Date, item.WeekOfMonth);
        }

        var final = Console.ReadLine();
    }
}

public static class DateTimeExtensions
{
    public static int WeekOfMonth(this DateTime d)
    {
        var isExact = (d.Day % 7 == 0);
        var offset = isExact ? 0 : 1;
        return (int)Math.Floor(d.Day / 7.0) + offset;
    }
}

这是一个旧线程,但我需要像这样的东西,这是我想出的。

public static int WeekOfMonth(this DateTime date)
{
    DateTime firstDayOfMonth = new DateTime(date.Year, date.Month, 1);
    int firstDay = (int)firstDayOfMonth.DayOfWeek;
    if (firstDay == 0)
    {
        firstDay = 7;
    }
    double d = (firstDay + date.Day - 1) / 7.0;
    return (int)Math.Ceiling(d);
}

注意:如果您想使用星期一作为一周的第一天,则此选项应该有效。如果您希望本周从周日开始,那么在2015年3月的第2周以及其他日期都会失败。2015年3月9日星期一是第二周的第一天。上述计算结果返回该日期的“3”。

一旦你有了一个月的第一天的DayOfWeek,你就可以使用整数运算得到一个月的一周。

static class DateTimeExtensions
{
    // Assumes that in current culture week starts on Sunday
    public static int GetWeekOfMonth(this DateTimeOffset time)
    {
        DateTimeOffset first = new DateTimeOffset(time.Year, time.Month, 1, 0, 0, 0, time.Offset);
        int firstSunday = (7 - (int)first.DayOfWeek) % 7 + 1;
        int weekOfMonth = 1 + (time.Day + 7 - firstSunday) / 7;

        return weekOfMonth;
    }
}

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

private int WeeksNumber()
        {
            int daysInMonth = DateTime.DaysInMonth(YourYear, YourMonth);
            DateTime date = new DateTime(Year, Month, 1);
            switch (daysInMonth)
            {
                case 28:
                    {
                        if (date.DayOfWeek == DayOfWeek.Monday)
                        {
                            return 4;
                        }
                        else
                        {
                            return 5;
                        }
                    }
                case 29:
                    {
                        return 5;
                    }
                case 30:
                    {
                        if (date.DayOfWeek == DayOfWeek.Sunday)
                        {
                            return 6;
                        }
                        else
                        {
                            return 5;
                        }
                    }
                case 31:
                    {
                        if (date.DayOfWeek == DayOfWeek.Sunday || date.DayOfWeek == DayOfWeek.Saturday)
                        {
                            return 6;
                        }
                        else
                        {
                            return 5;
                        }
                    }
                default: return 5;
            }
        } 

  Dim mdt As Date = txtDT.Text
    Dim weekNum As Integer = CultureInfo.CurrentCulture.Calendar.GetWeekOfYear(mdt, CalendarWeekRule.FirstFourDayWeek, DayOfWeek.Sunday) - CultureInfo.CurrentCulture.Calendar.GetWeekOfYear(GetFirstDayOfMonth(mdt), CalendarWeekRule.FirstFourDayWeek, DayOfWeek.Sunday) + 1
    Response.Write(weekNum)

为什么不像这个扩展那么简单?

public static int WeekNumber( this DateTime d )
{
    int w = 0;

    if ( d.Day <= 7 )
    {
        w = 1;
    }
    else if ( d.Day > 7 && d.Day <= 14 )
    {
        w = 2;
    }
    else if ( d.Day > 14 && d.Day <= 21 )
    {
        w = 3;
    }
    else if ( d.Day > 21 && d.Day <= 28 )
    {
        w = 4;
    }
    else if ( d.Day > 28 )
    {
        w = 5;
    }

    return w;
}