Question

即：

  NSDate *firstDayOfWeek = [[NSDate date] firstDayOfWeek];

例如，今天是8月19日，我想从上面的代码行中获得NSDate 2010-08-15 12:00am。谢谢！

Answer 1

我认为这些主题会回应你所寻找的内容：http://www.cocoabuilder.com/archive/cocoa/211648-nsdatecomponents-question.html#211826

但请注意，它不会将星期一作为一周的第一天处理，因此您可能需要通过减去[gregorian firstWeekday]而不仅仅1来稍微调整一下。另外，我修改它以使用-currentCalendar，但这取决于你： - ）

NSDate *today = [NSDate date];
NSCalendar *gregorian = [NSCalendar currentCalendar];

// 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];
/* Substract [gregorian firstWeekday] to handle first day of the week being something else than Sunday */
[componentsToSubtract setDay: - ([weekdayComponents weekday] - [gregorian firstWeekday])];
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];

Answer 2

为什么这么复杂？：）

func firstDateOfWeekWithDate(date: NSDate) -> NSDate {

    var beginningOfWeek: NSDate?

    calendar.rangeOfUnit(.WeekOfYear, startDate: &beginningOfWeek, interval: nil, forDate: date)

    return beginningOfWeek!

}

Answer 3

如果星期一（2）设置为第一周，并且您正在检查的日期是星期日，则naixn的解决方案将产生错误的结果。在这种情况下，你将得到下周一的星期一。

正确的方法是按如下方式计算减法分量：

[componentsToSubtract setDay: - ((([weekdayComponents weekday] - [gregorian firstWeekday])
                                  + 7 ) % 7)];

假设你一周有7天。

Answer 4

- (NSDate *)firstDateOfWeekWithDate:(NSDate *)date {

    NSCalendar * calendar = [NSCalendar currentCalendar];

    NSDateComponents *weekdayComponents = [calendar components:(NSDayCalendarUnit | NSWeekdayCalendarUnit) fromDate:date];

    NSDateComponents *components = [calendar components:(NSYearCalendarUnit | NSMonthCalendarUnit | NSDayCalendarUnit | NSWeekdayCalendarUnit) fromDate:date];
    [components setDay:-((([weekdayComponents weekday] - [calendar firstWeekday]) + 5 ) % 7)];

    return [calendar dateFromComponents:components];
}

Answer 5

这已经得到了解答，但是Wolfgang has pointed out，接受的答案中有一个错误。如果将第一个工作日设置为比相关UPDATE `myTable` SET `CastLotNo` = (SELECT `LotNo` FROM `MyTable` WHERE `OperationCode` = '1280' LIMIT 1) WHERE `CastTID` = (SELECT `CastTID` FROM `MyTable` WHERE `OperationCode` = '1280' LIMIT 1)更大的日期，则结果将不正确。这是一个适用于所有可能的NSDate值的完整解决方案（该示例使用星期一）。

firstWeekday

Answer 6

最简单的解决方案：

func firstDayOfWeek(date: NSDate) -> NSDate {
  let calendar = NSCalendar.currentCalendar()
  var dateComponents = calendar.components(.CalendarUnitYear | .CalendarUnitMonth | .CalendarUnitWeekOfMonth, fromDate: date)
  dateComponents.weekday = 1
  return calendar.dateFromComponents(dateComponents)!
}

Answer 7

使用NSDateComponents并将weekday设置为1。

Answer 8

对于Swift 4.1：

extension Date {
  var startOfWeek: Date? {
        let calendar = Calendar(identifier: .gregorian)
        return calendar.date(from: calendar.dateComponents([.yearForWeekOfYear, .weekOfYear], from: self))
    }
}

如何计算当前第一周的NSDate？

8 个答案: