计算日历周

使用 NSCalendar 和 NSDateComponents .

NSCalendar *cal = [NSCalendar currentCalendar];
NSDateComponents *components = [cal components:NSWeekCalendarUnit fromDate:date];
NSInteger week = [components week];

或使用:

CFAbsoluteTime currentTime = CFAbsoluteTimeGetCurrent();
CFTimeZoneRef currentTimeZone = CFTimeZoneCopyDefault();    
SInt32 weekNumber = CFAbsoluteTimeGetWeekOfYear(currentTime, currentTimeZone);

编号遵循ISO 8601对周的定义。

NSDate *today = [NSDate date];
NSCalendar *ISO8601 = [[NSCalendar alloc] initWithCalendarIdentifier:NSCalendarIdentifierISO8601];
ISO8601.firstWeekday = 2; // Sunday = 1, Saturday = 7
ISO8601.minimumDaysInFirstWeek = 4;
NSDateComponents *components = [ISO8601 components:NSCalendarUnitWeekOfYear fromDate:today];
NSUInteger weekOfYear = [components weekOfYear];
NSDate *mondaysDate = nil;
[ISO8601 rangeOfUnit:NSCalendarUnitYearForWeekOfYear startDate:&mondaysDate interval:NULL forDate:today];
NSLog(@"The current Weeknumber of Year %ld ", weekOfYear);

NSDateFormatter 像这样:

NSDateFormatter *fm = [[NSDateFormatter alloc] initWithDateFormat:@"ww" allowNaturalLanguage:NO];
NSString *week = [fm stringFromDate: date];

Week number according to the ISO-8601 standard, weeks starting on Monday. The first week of the year is the week that contains that year's first Thursday (='First 4-day week'). The highest week number in a year is either 52 or 53. This year has 52 weeks.This is not the only week numbering system in the world, other systems use weeks starting on Sunday (US) or Saturday (Islamic).

更多详细信息: http://www.epochconverter.com/weeknumbers

苹果也支持这一点,所以你可以从中找到正确的方法 https://developer.apple.com/library/mac/documentation/Cocoa/Reference/Foundation/Classes/NSCalendar_Class/

ISO-8601 standard :

NSCalendar *ISO8601 = [[NSCalendar alloc] initWithCalendarIdentifier:NSCalendarIdentifierISO8601];

希望这能有所帮助。