cocoa-touch - 从周数计算日期

Question

如何计算只有星期数和星期几的日期？

例如，第 24 周，星期二，2012，星期从星期一开始。

Answer 1

非常方便，NSCalendar 会为你做所有的数学计算。首先，使用 NSDateComponents 设置参数：

NSDateComponents *comps = [[NSDateComponents alloc] init];
[comps setWeek:24];
[comps setWeekday:3]; //map weekday names to numbers (e.g., Sunday is 1)
[comps setYear:2012];

然后使用这些日期组件创建一个公历：

 NSCalendar *gregorian = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];

并抓住你的 NSDate：

 NSDate *date = [gregorian dateFromComponents:comps];

Answer 2

    NSDate *now = [NSDate date];
    NSCalendar *gregorian = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];
    NSDateComponents *comp = [gregorian components:NSYearCalendarUnit fromDate:now];
    [comp setWeek:24];
    [comp setDay:1]; 
    NSDate *resultDate = [gregorian dateFromComponents:comp];
    NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
    [formatter setDateFormat:@"MMM d, yyyy"];


    NSString *myDateString = [formatter stringFromDate:resultDate];

    [gregorian release]; // Clean up allocated objects by releasing them
    [formatter release];

    NSString * date = [NSString stringWithFormat:@"Week of %@", myDateString];