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GetWeekOfYear  
Method  
Return the DateTime Week of Year according to the current Calendar
Calendar Class
System.Globalization NameSpace
CF1.  Function GetWeekOfYear ( TheDateTime:DateTimeTheDateTime : DateTime; CalendarRule : CalendarWeekRule; FirstDayOfWeek : DayOfWeek; ) : Integer;
CF : Methods with this mark are Compact Framework Compatible
Description
Returns the Week of Year value from TheDateTime value according to the current Calendar culture.
 
The GetWeekOfYear method converts the ticks value in TheDateTime (1 tick = 0.0000001 seconds since 1st Jan 0001 AD) into an internal representation of years, months, days according to the Calendar culture. It then returns the Week of year value according to this culture.
 
For example, in the Hebrew Calendar, there are between 353 and 355 days per common year, and 383 to 385 days in a leap year.]
 
It uses the CalendarRule and FirstDayOfWeek values to calculate the week of the year.
References
DateTime
CultureInfo
CalendarWeekRule
DayOfWeek
Microsoft MSDN Links
System.Globalization
System.Globalization.Calendar
 
 
Getting the Week of Year for British and Arabic cultures
program Project1;
{$APPTYPE CONSOLE}

uses
  System.Globalization;

var
  myDate    : DateTime;

  gbCulture : System.Globalization.CultureInfo;
  saCulture : System.Globalization.CultureInfo;

  gbCal     : System.Globalization.Calendar;
  saCal     : System.Globalization.Calendar;

  gbWeek    : Integer;  // British week in year
  saWeek    : Integer;  // Arabic  week in year

begin
  // Set up a Great Britain English culture & calendar
  gbCulture := System.Globalization.CultureInfo.Create('en-GB');
  gbCal     := gbCulture.Calendar;

  // Set up a Saudi Arabia Arabic culture & calendar
  saCulture := System.Globalization.CultureInfo.Create('ar-SA');
  saCal     := saCulture.Calendar;

  // Create a DateTime object : use the gbCalendar to control the
  // conversion of year, month and day parameter values into the
  // number of ticks since 1st January 0001 AD (the internal value)
  // Note : Gregorian Calendar is used by default anyway
  myDate := DateTime.Create(2004, 12, 8, gbCal);  // 8th December 2004

  // Get the British week in the year
  gbWeek := gbCal.GetWeekOfYear(myDate,
                                gbCulture.DateTimeFormat.CalendarWeekRule,
                                gbCulture.DateTimeFormat.FirstDayOfWeek);

  // Get the Arabic week in the year
  saWeek := saCal.GetWeekOfYear(myDate,
                                saCulture.DateTimeFormat.CalendarWeekRule,
                                saCulture.DateTimeFormat.FirstDayOfWeek);

  // Now use the British calendar object to display this date
  Console.WriteLine('British calendar :');
  Console.WriteLine;
  Console.WriteLine('Year           = {0}', gbCal.GetYear(myDate).ToString);
  Console.WriteLine('Month          = {0}', gbCal.GetMonth(myDate).ToString);
  Console.WriteLine('Day of   month = {0}', gbCal.GetDayOfMonth(myDate).ToString);
  Console.WriteLine('Week of   year = {0}', gbWeek.ToString);

  // Now use the Arabic calendar object to display this date
  Console.WriteLine;
  Console.WriteLine('Arabic calendar :');
  Console.WriteLine;
  Console.WriteLine('Year           = {0}', saCal.GetYear(myDate).ToString);
  Console.WriteLine('Month          = {0}', saCal.GetMonth(myDate).ToString);
  Console.WriteLine('Day of   month = {0}', saCal.GetDayOfMonth(myDate).ToString);
  Console.WriteLine('Week of   year = {0}', saWeek.ToString);

  Console.ReadLine;
end.
Show full unit code
  British calendar :
  
  Year           = 2004
  Month          = 12
  Day of   month = 8
  Week of   year = 50
  
  Arabic calendar :
  
  Year           = 1425
  Month          = 10
  Day of   month = 26
  Week of   year = 42
Using different criteria for the first week of the year
program Project1;
{$APPTYPE CONSOLE}

uses
  System.Globalization;

var
  gbCulture : System.Globalization.CultureInfo;
  gbCal     : System.Globalization.Calendar;

  date      : DateTime;

  day       : Integer;
  week      : Integer;

begin
  // Set up a Great Britain English culture & calendar
  gbCulture := System.Globalization.CultureInfo.Create('en-GB');
  gbCal     := gbCulture.Calendar;

  Console.WriteLine('Using CalendarWeekRule.FirstDay :');
  Console.WriteLine;

  for day := 1 to 7 do
  begin
    date := DateTime.Create(2004, 1, day, gbCal);

    week := gbCal.GetWeekOfYear(date,
                                CalendarWeekRule.FirstDay,
                                DayOfWeek.Monday);

    Console.WriteLine('{0} is in week {1}',
                      date.ToString('ddd dd MMM yyyy'),
                      week.ToString);
  end;

  Console.WriteLine;
  Console.WriteLine('Using CalendarWeekRule.FirstFullWeek :');
  Console.WriteLine;

  for day := 1 to 7 do
  begin
    date := DateTime.Create(2004, 1, day, gbCal);

    week := gbCal.GetWeekOfYear(date,
                                CalendarWeekRule.FirstFullWeek,
                                DayOfWeek.Monday);

    Console.WriteLine('{0} is in week {1}',
                      date.ToString('ddd dd MMM yyyy'),
                      week.ToString);
  end;

  Console.WriteLine;
  Console.WriteLine('Using CalendarWeekRule.FirstFourDayWeek :');
  Console.WriteLine;

  for day := 1 to 7 do
  begin
    date := DateTime.Create(2004, 1, day, gbCal);

    week := gbCal.GetWeekOfYear(date,
                                CalendarWeekRule.FirstFourDayWeek,
                                DayOfWeek.Monday);

    Console.WriteLine('{0} is in week {1}',
                      date.ToString('ddd dd MMM yyyy'),
                      week.ToString);
  end;

  Console.ReadLine;
end.
Show full unit code
  Using CalendarWeekRule.FirstDay :
  
  Thu 01 Jan 2004 is in week 1
  Fri 02 Jan 2004 is in week 1
  Sat 03 Jan 2004 is in week 1
  Sun 04 Jan 2004 is in week 1
  Mon 05 Jan 2004 is in week 2
  Tue 06 Jan 2004 is in week 2
  Wed 07 Jan 2004 is in week 2
  
  Using CalendarWeekRule.FirstFullWeek :
  
  Thu 01 Jan 2004 is in week 52
  Fri 02 Jan 2004 is in week 52
  Sat 03 Jan 2004 is in week 52
  Sun 04 Jan 2004 is in week 52
  Mon 05 Jan 2004 is in week 1
  Tue 06 Jan 2004 is in week 1
  Wed 07 Jan 2004 is in week 1
  
  Using CalendarWeekRule.FirstFourDayWeek :
  
  Thu 01 Jan 2004 is in week 1
  Fri 02 Jan 2004 is in week 1
  Sat 03 Jan 2004 is in week 1
  Sun 04 Jan 2004 is in week 1
  Mon 05 Jan 2004 is in week 2
  Tue 06 Jan 2004 is in week 2
  Wed 07 Jan 2004 is in week 2
 
 
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