如何在Objective-C的特殊日期中获得一周的星期一？

Question

例如2010年10月10日是星期五=> 2010年9月27日是星期一。

我不知道如何处理这一个。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拿周日在本周

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]; 

---

2014年3月

其实还有一个更聪明的方式

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 

如果你确实改变平日代表本周的开始（周日vs 。星期一），你应该在这段代码后改回它。