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Calendar.GetWeekOfYear Method

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Updated: October 2010

Returns the week of the year that includes the date in the specified DateTime value.

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

Syntax

'Declaration
Public Overridable Function GetWeekOfYear ( _
    time As DateTime, _
    rule As CalendarWeekRule, _
    firstDayOfWeek As DayOfWeek _
) As Integer

public virtual int GetWeekOfYear(
    DateTime time,
    CalendarWeekRule rule,
    DayOfWeek firstDayOfWeek
)

Parameters

Return Value

Type: System.Int32
A positive integer that represents the week of the year that includes the date in the time parameter.

Exceptions

Exception Condition
ArgumentOutOfRangeException

time is earlier than MinSupportedDateTime or later than MaxSupportedDateTime.

-or-

firstDayOfWeek is not a valid DayOfWeek value.

-or-

rule is not a valid CalendarWeekRule value.

Remarks

This method can be used to determine the number of weeks in the year by setting time to the last day of the year.

The DateTimeFormatInfo object for a particular culture that uses the calendar indicated by the DateTimeFormatInfo.Calendar property includes the following culture-specific values that can be used for the rule and firstDayOfWeek parameters:

The following example uses the current culture's DateTimeFormatInfo object to determine that January 1, 2011 is in the first week of the year in the Gregorian calendar.

Imports System.Globalization

Module Example
   Public Sub Demo(ByVal outputBlock As System.Windows.Controls.TextBlock)
      Dim dfi As DateTimeFormatInfo = DateTimeFormatInfo.CurrentInfo
      Dim date1 As Date = #1/1/2011#
      Dim cal As Calendar = dfi.Calendar

      outputBlock.Text += String.Format("{0:d}: Week {1} ({2})", date1, 
                        cal.GetWeekOfYear(date1, dfi.CalendarWeekRule, 
                                          dfi.FirstDayOfWeek),
                        cal.ToString().Substring(cal.ToString().LastIndexOf(".") + 1)) _  
                        & vbCrLf      
   End Sub
End Module
' The example displays the following output:
'       1/1/2011: Week 1 (GregorianCalendar)

using System;
using System.Globalization;

public class Example
{
   public static void Demo(System.Windows.Controls.TextBlock outputBlock)
   {
      DateTimeFormatInfo dfi = DateTimeFormatInfo.CurrentInfo;
      DateTime date1 = new DateTime(2011, 1, 1);
      Calendar cal = dfi.Calendar;

      outputBlock.Text += String.Format("{0:d}: Week {1} ({2})", date1,
                        cal.GetWeekOfYear(date1, dfi.CalendarWeekRule,
                                          dfi.FirstDayOfWeek),
                        cal.ToString().Substring(cal.ToString().LastIndexOf(".") + 1)) + "\n";
   }
}
// The example displays the following output:
//       1/1/2011: Week 1 (GregorianCalendar)

For some calendars, a call to the GetWeekOfYear method throws an ArgumentOutOfRangeException for particular combinations of rule and firstDayOfWeek values even if time is greater than the date returned by that calendar's MinSupportedDateTime property. The following table lists the affected calendars, the specific rule values, and the range of the earliest supported time values. The specific minimum DateTime value depends on the value of the firstDayOfWeek parameter.

Calendar

CalendarWeekRule value

Gregorian date (M/dd/yyyy)

Date in calendar (M/dd/yyyy)

ChineseLunisolarCalendar

FirstFullWeek

2/19/1901 to 2/25/1901

1/1/1901 to 1/7/1901

ChineseLunisolarCalendar

FirstFourDayWeek

2/19/1901 to 2/22/1901

1/01/1901 to 1/04/1901

HebrewCalendar

FirstDay

9/17/1583

1/01/5344

HebrewCalendar

FirstFullWeek

9/17/1583 to 9/23/1583

1/01/5344 to 1/07/5344

HebrewCalendar

FirstFourDayWeek

9/17/1583 to 9/20/1583

1/01/5344 to 1/04/5344

HijriCalendar

FirstFullWeek

7/18/0622 to 7/24/0622

1/01/0001 to 1/07/0001

HijriCalendar

FirstFourDayWeek

7/18/0622 to 7/21/0622

1/01/0001 to 1/04/0001

JapaneseLunisolarCalendar

FirstFullWeek

1/28/1960 to 2/03/1960

1/01/35 to 1/07/0035

JapaneseLunisolarCalendar

FirstFourDayWeek

1/28/1960 to 1/31/1960

1/01/0035 to 1/04/0035

JulianCalendar

FirstFullWeek

1/01/0001 to 1/05/0001

1/03/0001 to 1/07/0001

JulianCalendar

FirstFourDayWeek

1/01/0001 to 1/02/0001

1/03/0001 to 1/04/0001

KoreanLunisolarCalendar

FirstFullWeek

2/14/0918 to 2/20/0918

1/01/0918 to 1/07/0918

KoreanLunisolarCalendar

FirstFourDayWeek

2/14/0918 to 2/17/0918

1/01/0918 to 1/04/0918

PersianCalendar

FirstFullWeek

3/21/0622 to 3/27/0622

1/01/0001 to 1/07/0001

PersianCalendar

FirstFourDayWeek

3/21/0622 to 3/24/0622

1/01/0001 to 1/04/0001

TaiwanLunisolarCalendar

FirstFullWeek

2/18/1912 to 2/24/1912

1/01/0001 to 1/07/0001

TaiwanLunisolarCalendar

FirstFourDayWeek

2/18/1912 to 2/21/1912

1/01/0001 to 1/04/0001

UmAlQuraCalendar

FirstFullWeek

4/30/1900 to 5/06/1900

1/01/1318 to 1/07/1318

UmAlQuraCalendar

FirstFourDayWeek

4/30/1900 to 5/03/1900

1/01/1318 to 1/04/1318

Examples

The following example shows how the result of GetWeekOfYear varies depending on the FirstDayOfWeek and the CalendarWeekRule used. If the specified date is the last day of the year, GetWeekOfYear returns the total number of weeks in that year.

Imports System.Globalization

Public Class Example

   Public Shared Sub Demo(ByVal outputBlock As System.Windows.Controls.TextBlock)

      ' Gets the Calendar instance associated with a CultureInfo.
      Dim myCI As New CultureInfo("en-US")
      Dim myCal As Calendar = myCI.Calendar

      ' Gets the DTFI properties required by GetWeekOfYear.
      Dim myCWR As CalendarWeekRule = myCI.DateTimeFormat.CalendarWeekRule
      Dim myFirstDOW As DayOfWeek = myCI.DateTimeFormat.FirstDayOfWeek

      ' Displays the number of the current week relative to the beginning of the year.
      outputBlock.Text += String.Format("The CalendarWeekRule used for the en-US culture is {0}.", myCWR) & vbCrLf
      outputBlock.Text += String.Format("The FirstDayOfWeek used for the en-US culture is {0}.", myFirstDOW) & vbCrLf
      outputBlock.Text += String.Format("Therefore, the current week is Week {0} of the current year.", myCal.GetWeekOfYear(DateTime.Now, myCWR, myFirstDOW)) & vbCrLf

      ' Displays the total number of weeks in the current year.
      Dim LastDay = New System.DateTime(DateTime.Now.Year, 12, 31)
      outputBlock.Text += String.Format("There are {0} weeks in the current year ({1}).", myCal.GetWeekOfYear(LastDay, myCWR, myFirstDOW), LastDay.Year) & vbCrLf
   End Sub 'Main 
End Class 'SamplesCalendar


'This code produces the following output.  Results vary depending on the system date.
'
'The CalendarWeekRule used for the en-US culture is FirstDay.
'The FirstDayOfWeek used for the en-US culture is Sunday.
'Therefore, the current week is Week 1 of the current year.
'There are 53 weeks in the current year (2001).


using System;
using System.Globalization;


public class Example
{

   public static void Demo(System.Windows.Controls.TextBlock outputBlock)
   {

      // Gets the Calendar instance associated with a CultureInfo.
      CultureInfo myCI = new CultureInfo("en-US");
      Calendar myCal = myCI.Calendar;

      // Gets the DTFI properties required by GetWeekOfYear.
      CalendarWeekRule myCWR = myCI.DateTimeFormat.CalendarWeekRule;
      DayOfWeek myFirstDOW = myCI.DateTimeFormat.FirstDayOfWeek;

      // Displays the number of the current week relative to the beginning of the year.
      outputBlock.Text += String.Format("The CalendarWeekRule used for the en-US culture is {0}.", myCWR) + "\n";
      outputBlock.Text += String.Format("The FirstDayOfWeek used for the en-US culture is {0}.", myFirstDOW) + "\n";
      outputBlock.Text += String.Format("Therefore, the current week is Week {0} of the current year.", myCal.GetWeekOfYear(DateTime.Now, myCWR, myFirstDOW)) + "\n";

      // Displays the total number of weeks in the current year.
      DateTime LastDay = new System.DateTime(DateTime.Now.Year, 12, 31);
      outputBlock.Text += String.Format("There are {0} weeks in the current year ({1}).", myCal.GetWeekOfYear(LastDay, myCWR, myFirstDOW), LastDay.Year) + "\n";

   }

}

/*
This code produces the following output.  Results vary depending on the system date.

The CalendarWeekRule used for the en-US culture is FirstDay.
The FirstDayOfWeek used for the en-US culture is Sunday.
Therefore, the current week is Week 1 of the current year.
There are 53 weeks in the current year (2001).

*/

Version Information

Silverlight

Supported in: 5, 4, 3

Silverlight for Windows Phone

Supported in: Windows Phone OS 7.1, Windows Phone OS 7.0

XNA Framework

Supported in: Xbox 360, Windows Phone OS 7.0

Platforms

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.

Change History

Date

History

Reason

October 2010

Noted that in some cases an exception can be thrown for dates later than MinSupportedDateTime.

Content bug fix.

October 2010

Added a discussion of DateTimeFormatInfo properties and an example.

Information enhancement.