Question

我知道有一些问题与此类似，但我无法找到我的代码有什么问题。

基本上我想要的是如果今天不是星期日，则currentDate设置为最后一个星期日。如果今天是星期天，我当前的日期将被设定为星期天。

以下是我试图做的事情。

  NSDateComponents *components = [[NSCalendar currentCalendar] components:  NSWeekCalendarUnit | NSYearCalendarUnit | NSWeekdayCalendarUnit fromDate:currentDate];

    if (components.weekday == 1) { //Its sunday. We just need to subtract a week
        [components setWeek: -1];
        currentDate = [[NSCalendar currentCalendar] dateByAddingComponents:components toDate:currentDate options:0];

    }else{ //If its not sunday we just go to sunday
        [components setWeekday: 1];
        currentDate = [[NSCalendar currentCalendar] dateFromComponents:components];

    }

第一次执行这部分代码时，我得到了正确的答案。在我第一次得到奇怪的日期之后，比如4026年12月02日，这一年不断上升。

以下是使其有效的代码：

   NSCalendar *calendar = [NSCalendar currentCalendar];
    NSDateComponents *components = [calendar components: ( NSWeekCalendarUnit | NSWeekdayCalendarUnit | NSYearCalendarUnit) fromDate:currentDate];
    int weekday = components.weekday;

    if (weekday == 1) {
        [components setWeek:components.week -1];
    }else{
        [components setWeekday:1];
    }
    currentDate = [calendar dateFromComponents:components];

Answer 1

如果您使用的是iOS 8.0 +

，请使用nextDateAfterDate和.SearchBackwards选项

let calendar = NSCalendar.currentCalendar()
let options: NSCalendarOptions = [.MatchPreviousTimePreservingSmallerUnits, .SearchBackwards]
calendar.nextDateAfterDate(NSDate(), matchingUnit: .Weekday, value: 1, options: options)

Answer 2

在NSCalendar上尝试此类别

@interface NSCalendar (LastSunday)
-(NSDate *)previousSundayForDate:(NSDate *)date;
@end

@implementation NSCalendar (LastSunday)

-(NSDate *)previousSundayForDate:(NSDate *)date
{
    static NSUInteger SUNDAY = 1;
    static NSUInteger MONDAY = 2;

    NSDate *startOfWeek;
    [self rangeOfUnit:NSWeekCalendarUnit
            startDate:&startOfWeek
             interval:NULL
              forDate:date];

    if(self.firstWeekday == SUNDAY){

        NSDate *beginningOfDate;
        [self rangeOfUnit:NSDayCalendarUnit
                startDate:&beginningOfDate
                 interval:NULL forDate:date];
        if ([startOfWeek isEqualToDate:beginningOfDate]) {
            startOfWeek = [self dateByAddingComponents:(
                                                        {
                                                            NSDateComponents *comps = [[NSDateComponents alloc] init];
                                                            comps.day = -7;
                                                            comps;
                                                        })
                                                toDate:startOfWeek
                                               options:0];
        }
        return startOfWeek;
    }
    if(self.firstWeekday == MONDAY)
        return [self dateByAddingComponents:(
                                             {
                                                 NSDateComponents *comps = [[NSDateComponents alloc] init];
                                                 comps.day = -1;
                                                 comps;
                                             })
                                     toDate:startOfWeek
                                    options:0];

    return nil;

}

@end

将其用作：

NSDate *lastSunday = [calendar previousSundayForDate:[NSDate date]];

PS：

“one-method-one-return-statement”的版本 - fetishists：

@implementation NSCalendar (LastSunday)

-(NSDate *)previousSundayForDate:(NSDate *)date
{
    NSDate *resultDate = nil;
    static NSUInteger SUNDAY = 1;
    static NSUInteger MONDAY = 2;

    NSDate *startOfWeek;
    [self rangeOfUnit:NSWeekCalendarUnit
            startDate:&startOfWeek
             interval:NULL
              forDate:date];

    if(self.firstWeekday == SUNDAY){

        NSDate *beginningOfDate;
        [self rangeOfUnit:NSDayCalendarUnit
                startDate:&beginningOfDate
                 interval:NULL forDate:date];

        if ([startOfWeek isEqualToDate:beginningOfDate]) {
            startOfWeek = [self dateByAddingComponents:(
                                                        {
                                                            NSDateComponents *comps = [[NSDateComponents alloc] init];
                                                            comps.day = -7;
                                                            comps;
                                                        })
                                                toDate:startOfWeek
                                               options:0];
        }
        resultDate = startOfWeek;
    }
    if(self.firstWeekday == MONDAY)
        resultDate = [self dateByAddingComponents:(
                                                   {
                                                       NSDateComponents *comps = [[NSDateComponents alloc] init];
                                                       comps.day = -1;
                                                       comps;
                                                   })
                                           toDate:startOfWeek
                                          options:0];

    return resultDate;

}

@end

Answer 3

你得到4026的原因是因为这一行：

NSDateComponents *components = [[NSCalendar currentCalendar] components:  NSWeekCalendarUnit | NSYearCalendarUnit | NSWeekdayCalendarUnit fromDate:currentDate];

它将年度组件设置为当前年份，2013年。它还初始化周和工作日组件。然后将组件添加到当前日期，将年份翻倍至4026，此处：

[components setWeek: -1];
currentDate = [[NSCalendar currentCalendar] dateByAddingComponents:components toDate:currentDate options:0];

如果您只想减去一周，请按以下步骤减去：

NSDateComponents *components = [[NSDateComponents alloc] init];
[components setWeek: -1];
currentDate = [[NSCalendar currentCalendar] dateByAddingComponents:components toDate:currentDate options:0];
[components release];

NSDateComponents / NSDate：获取最后一个星期日

3 个答案: