NSDateComponents将时间表示成适合人类阅读和使用的方式, 首先要遵循某种历法

NSCalendar * cal = [NSCalendar currentCalendar];

有三种用法:

1.获取某个时间点的NSDateComponents表示

unsigned int unitFlags = NSYearCalendarUnit | NSMonthCalendarUnit | NSDayCalendarUnit

                                    | NSHourCalendarUnit | NSMinuteCalendarUnit | NSSecondCalendarUnit;

NSDateComponents * Comps = [cal components:unitFlags fromDate:[NSDate date]];

可获取到comps.year,  comps.mouth ,  comps.weekday(周几), dateComponents.week(该年第几周)

2.定义一个NSDateComponents对象，设置一个时间点

NSDateComponents *Comps = [[NSDateComponents alloc] init];

[Comps setDay:6];

[Comps setMonth:5];

[Comps setYear:2004];

NSDate* date = [[NSCalendar currentCalendar] dateFromComponents:Comps];

// 定义一个NSDateComponents对象，设置一个时间段

NSDateComponents *comps = [[NSDateComponents alloc] init];

[comps setDay:6]; // 在当前历法下，获取6天后的时间点

NSDate *dateLater = [cal dateByAddingComponents:comps toDate:[NSDate date] options:0];

3.获取两个时间点的时差

NSDateComponents *dateComponents = [greCalendar components:NSYearCalendarUnit fromDate:[NSDate dateWithTimeIntervalSince1970:0] toDate:[NSDate date] options:0];

NSLog(@"%d", dateComponents.year);

NSDateComponents