在上午12:00动态创建上一个星期日的日期 [英] dynamically create date for previous sunday at 12:00 AM

问题描述

我正在努力弄清楚如何在上午12:00的最前一个星期日动态创建一个日期对象

I'm struggling to figure out how to dynamically create a date object for the most previous sunday at 12:00 AM

我以为我今天可以得到日期然后减去当周的当天+ 1，此时我可以减去当天的时间到达上午12点。

I was thinking I could get today's date and then subtract the current day of the week + 1 at which point I could just subtract the time of the day do get down to 12AM.

到目前为止，我有当前的星期几：

so far I have the current day of the week:

NSCalendar *gregorian = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];
NSDateComponents *comps = [gregorian components:NSWeekdayCalendarUnit fromDate:[NSDate date]];
int weekday = [comps weekday];

此时我可以获得今天的日期并减去工作日的差异一天中的*秒。但是，我怎样才能在几秒钟内获得今天的时间？

at which point I can get today's date and subtract the difference of weekday * seconds in a day. However, how can I get today's time in seconds ??

推荐答案

无需手动计算秒数（这无论如何都是危险的夏令时等）。以下内容应该完全符合您的要求：

No need to manually calculate seconds (which is dangerous anyway because of daylight saving etc.). The following should do exactly what you want:

NSDate *today = [NSDate date];
NSCalendar *calendar = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];
[calendar setLocale:[[NSLocale alloc] initWithLocaleIdentifier:@"en-US"]]; // force US locale, because other countries (e.g. the rest of the world) might use different weekday numbering

NSDateComponents *nowComponents = [calendar components:NSYearCalendarUnit | NSWeekCalendarUnit | NSHourCalendarUnit | NSMinuteCalendarUnit | NSSecondCalendarUnit fromDate:today];

[nowComponents setWeekday:1]; //Sunday
[nowComponents setHour:0]; // 12:00 AM = midnight (12:00 PM would be 12)
[nowComponents setMinute:0];
[nowComponents setSecond:0];

NSDate *previousSunday = [calendar dateFromComponents:nowComponents];

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