可可在一周内获得第一天 [英] Cocoa get first day in week

问题描述

如何获得一周的第一天约会

How to get the first day of a week for a date

这似乎更容易，因为：

• 当星期一开始星期日时，我需要回到星期日日期


• 如果它在星期一开始，我需要得到星期一日期

输入日期是一周中的任何日期与时间...我尝试了几种方法，但边缘情况使它难以理解

the input date is any date in week with time... i tried several approaches, but the edge case make it difficould

我做了一个函数，然而它不能100％工作（不确定[components setDay：-weekday + 2];）

i made a function, which however doesn't work in 100% (not sure about the [components setDay: -weekday + 2];)

- (NSDate *)firstDateOfWeek {

    NSCalendar * calendar = [NSCalendar currentCalendar];

    NSDateComponents *weekdayComponents = [calendar components:(NSDayCalendarUnit | NSWeekdayCalendarUnit) fromDate:self];
    // because sunday is 0, we need it to be 6
    NSInteger weekday = (([weekdayComponents weekday] + 6) % 7);

    NSDateComponents *components = [calendar components:(NSYearCalendarUnit | NSMonthCalendarUnit | NSDayCalendarUnit | NSWeekdayCalendarUnit) fromDate:self];
    [components setDay: -weekday + 2];

    return [calendar dateFromComponents:components];

}

推荐答案

这是更容易使用 rangeOfUnit 日历方法，该方法根据当前区域设置正确处理一周开始：

It is easier to use the rangeOfUnit calendar method, which handles "start of the week" correctly according to the current locale:

NSDate *date = your date;
NSCalendar *calendar = [NSCalendar currentCalendar];
NSDate *startOfWeek;
[calendar rangeOfUnit:NSWeekOfYearCalendarUnit
            startDate:&startOfWeek
             interval:NULL
              forDate:date];

使用 NSDateComponents ，它将如下工作（假设一周有7天）：

Using NSDateComponents, it would work as follows (assuming that a week has 7 days):

NSDate *date = your date;
NSDateComponents *comp = [calendar components:NSYearCalendarUnit|NSMonthCalendarUnit|NSDayCalendarUnit|NSWeekdayCalendarUnit
                                     fromDate:date];
NSDate *startOfDay = [calendar dateFromComponents:comp];
NSInteger diff = (NSInteger)[calendar firstWeekday] - (NSInteger)[comp weekday];
if (diff > 0)
    diff -= 7;
NSDateComponents *subtract = [[NSDateComponents alloc] init];
[subtract setDay:diff];
NSDate *startOfWeek = [calendar dateByAddingComponents:subtract toDate:startOfDay options:0];

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