如何在 Objective-C 中的特殊日期获得一周中的星期一？

Question

例如01.10.2010 是星期五 => 27.09.2010 是星期一。

我不知道如何管理这个。顺便说一句：我如何计算日期？

Answer 1

对于time/date calculations，使用 NSDateComponents。

清单 2 获取本周的星期日

NSDate *today = [[NSDate alloc] init];
NSCalendar *gregorian = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];

// Get the weekday component of the current date
NSDateComponents *weekdayComponents = [gregorian components:NSWeekdayCalendarUnit fromDate:today];

/*
Create a date components to represent the number of days to subtract from the current date.
The weekday value for Sunday in the Gregorian calendar is 1, so subtract 1 from the number of days to subtract from the date in question.  (If today's Sunday, subtract 0 days.)
*/
NSDateComponents *componentsToSubtract = [[NSDateComponents alloc] init];
[componentsToSubtract setDay: 0 - ([weekdayComponents weekday] - 1)];

NSDate *beginningOfWeek = [gregorian dateByAddingComponents:componentsToSubtract toDate:today options:0];

/*
Optional step:
beginningOfWeek now has the same hour, minute, and second as the original date (today).
To normalize to midnight, extract the year, month, and day components and create a new date from those components.
*/
NSDateComponents *components =
    [gregorian components:(NSYearCalendarUnit | NSMonthCalendarUnit | NSDayCalendarUnit)
               fromDate: beginningOfWeek];
beginningOfWeek = [gregorian dateFromComponents:components];

---

在以后的版本中，有更聪明的办法：

NSCalendar *cal = [NSCalendar currentCalendar];
[cal setFirstWeekday:2];    //2 is monday. 1:Sunday .. 7:Saturday don't set it, if user's locale should determine the start of a week
NSDate *now = [NSDate date];
NSDate *monday;
[cal rangeOfUnit:NSWeekCalendarUnit  // we want to have the start of the week
       startDate:&monday             // we will write the date object to monday
        interval:NULL                // we don't care for the seconds a week has
         forDate:now];               // we want the monday of today's week

如果您确实更改了表示一周开始的工作日（星期日与星期一），则应在此 sn-p 之后将其更改回来。