CalendarWeekRule Enumeration

Defines different rules for determining the first week of the year.

Namespace:  System.Globalization
Assembly:  mscorlib (in mscorlib.dll)

[SerializableAttribute]
[ComVisibleAttribute(true)]
public enum CalendarWeekRule

Member nameDescription
Supported by the XNA FrameworkSupported by Portable Class LibrarySupported in .NET for Windows Store appsFirstDayIndicates 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.
Supported by the XNA FrameworkSupported by Portable Class LibrarySupported in .NET for Windows Store appsFirstFourDayWeekIndicates 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.
Supported by the XNA FrameworkSupported by Portable Class LibrarySupported in .NET for Windows Store appsFirstFullWeekIndicates 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.

A member of the CalendarWeekRule enumeration is returned by the DateTimeFormatInfo.CalendarWeekRule property and is used by the culture's current calendar to determine the calendar week rule. The enumeration value is also used as a parameter to the Calendar.GetWeekOfYear method.

Calendar week rules depend on the System.DayOfWeek value that indicates the first day of the week in addition to depending on a CalendarWeekRule value. The DateTimeFormatInfo.FirstDayOfWeek property provides the default value for a culture, but any DayOfWeek value can be specified as the first day of the week in the Calendar.GetWeekOfYear method.

The first week based on the FirstDay value can have one to seven days. The first week based on the FirstFullWeek value always has seven days. The first week based on the FirstFourDayWeek value can have four to seven days.

For example, in the Gregorian calendar, suppose that the first day of the year (January 1) falls on a Tuesday and the designated first day of the week is Sunday. Selecting FirstFullWeek defines the first Sunday (January 6) as the beginning of the first week of the year. The first five days of the year are considered part of the last week of the previous year. In contrast, selecting FirstFourDayWeek defines the first day of the year (January 1) as the beginning of the first week of the year because there are more than four days from January 1 to the day before the following Sunday.

Date

FirstDay

FirstFullWeek

FirstFourDayWeek

Dec 31 Mon

Last week of the previous year

Last week of the previous year

Last week of the previous year

Jan 1 Tue

Week 1

Last week of the previous year

Week 1

Jan 2 Wed

Week 1

Last week of the previous year

Week 1

Jan 3 Thu

Week 1

Last week of the previous year

Week 1

Jan 4 Fri

Week 1

Last week of the previous year

Week 1

Jan 5 Sat

Week 1

Last week of the previous year

Week 1

Jan 6 Sun

Week 2

Week 1

Week 2

Jan 7 Mon

Week 2

Week 1

Week 2

Jan 8 Tue

Week 2

Week 1

Week 2

Jan 9 Wed

Week 2

Week 1

Week 2

Jan 10 Thu

Week 2

Week 1

Week 2

Jan 11 Fri

Week 2

Week 1

Week 2

Jan 12 Sat

Week 2

Week 1

Week 2

Suppose the first day of the year (January 1) falls on a Friday and the designated first day of the week is Sunday. Selecting FirstFourDayWeek defines the first Sunday (January 3) as the beginning of the first week of the year because there are fewer than four days from January 1 to the day before the following Sunday.

Date

FirstDay

FirstFullWeek

FirstFourDayWeek

Dec 31 Thu

Last week of the previous year

Last week of the previous year

Last week of the previous year

Jan 1 Fri

Week 1

Last week of the previous year

Last week of the previous year

Jan 2 Sat

Week 1

Last week of the previous year

Last week of the previous year

Jan 3 Sun

Week 2

Week 1

Week 1

Jan 4 Mon

Week 2

Week 1

Week 1

Jan 5 Tue

Week 2

Week 1

Week 1

Jan 6 Wed

Week 2

Week 1

Week 1

Jan 7 Thu

Week 2

Week 1

Week 1

Jan 8 Fri

Week 2

Week 1

Week 1

Jan 9 Sat

Week 2

Week 1

Week 1

The following example illustrates how the CalendarWeekRule and System.DayOfWeek values are used together to determine how weeks are assigned. In the Gregorian calendar, the first day of the year (January 1) in 2013 falls on a Tuesday. If the designated first day of the week is Sunday, the first Sunday (January 6) is the first day of the first week of the year, and Saturday (January 5) belongs to the fifty-third week of the previous year. Changing the calendar week rule to CalendarWeekRule.FirstFourDayWeek defines Tuesday (January 1) as the beginning of the first week of the year, because there are more than four days between Tuesday, January 1, and Sunday, January 6. Using this rule, January 5 belongs to the first week of the year. For 2010, a year in which January 1 falls on a Friday, applying the CalendarWeekRule.FirstFourDayWeek rule with DayOfWeek.Sunday as the first day of the week makes Sunday, January 3 the beginning of the first week of the year, because the first week in 2010 that has more than four days is January 3 through 9.

using System;
using System.Globalization;

public class Example
{
   static Calendar cal = new GregorianCalendar();

   public static void Main()
   {
      DateTime date = new DateTime(2013, 1, 5);
      DayOfWeek firstDay = DayOfWeek.Sunday;
      CalendarWeekRule rule;

      rule = CalendarWeekRule.FirstFullWeek;
      ShowWeekNumber(date, rule, firstDay);

      rule = CalendarWeekRule.FirstFourDayWeek;
      ShowWeekNumber(date, rule, firstDay);

      Console.WriteLine();
      date = new DateTime(2010, 1, 3);
      ShowWeekNumber(date, rule, firstDay);
   }

   private static void ShowWeekNumber(DateTime dat, CalendarWeekRule rule, 
                                      DayOfWeek firstDay)
   {                                   
      Console.WriteLine("{0:d} with {1:F} rule and {2:F} as first day of week: week {3}",
                        dat, rule, firstDay, cal.GetWeekOfYear(dat, rule, firstDay));
   }   
}
// The example displays the following output: 
//       1/5/2013 with FirstFullWeek rule and Sunday as first day of week: week 53 
//       1/5/2013 with FirstFourDayWeek rule and Sunday as first day of week: week 1 
//        
//       1/3/2010 with FirstFourDayWeek rule and Sunday as first day of week: week 1
NoteNote

This does not map exactly to ISO 8601. The differences are discussed in the blog entry ISO 8601 Week of Year format in Microsoft .Net.

Each CultureInfo object supports a set of calendars. The Calendar property returns the default calendar for the culture, and the OptionalCalendars property returns an array containing all the calendars supported by the culture. To change the calendar used by a CultureInfo, the application should set the Calendar property of CultureInfo.DateTimeFormat to a new Calendar.

.NET Framework

Supported in: 4.5.2, 4.5.1, 4.5, 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Portable Class Library

Supported in: Portable Class Library

.NET for Windows Store apps

Supported in: Windows 8

.NET for Windows Phone apps

Supported in: Windows Phone 8.1, Windows Phone 8, Silverlight 8.1

Windows Phone 8.1, Windows Phone 8, Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

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