日历计算

- components:fromDate:返回一个 NSDateComponents 对象，该对象包含分解为指定组件的给定日期

NSCalendar *calender = [NSCalendar autoupdatingCurrentCalendar];
[calender setTimeZone:[NSTimeZone timeZoneForSecondsFromGMT:0]];
NSLog(@"%@",[calender components:NSCalendarUnitDay fromDate:[NSDate date]]);
NSLog(@"%@",[calender components:NSCalendarUnitYear fromDate:[NSDate date]]);
NSLog(@"%@",[calender components:NSCalendarUnitMonth fromDate:[NSDate date]]);

- components:fromDate:toDate:options:使用指定组件作为 NSDateComponents 对象返回两个提供日期之间的差异。

 NSCalendar *calender = [NSCalendar autoupdatingCurrentCalendar];
[calender setTimeZone:[NSTimeZone timeZoneForSecondsFromGMT:0]];
NSLog(@"%@",[calender components:NSCalendarUnitYear fromDate:[NSDate dateWithTimeIntervalSince1970:0] toDate:[NSDate dateWithTimeIntervalSinceNow:18000] options:NSCalendarWrapComponents]);

- dateByAddingComponents:toDate:options:返回一个新的 NSDate 对象，表示通过将给定组件添加到给定日期而计算的绝对时间。

NSCalendar *calender = [NSCalendar autoupdatingCurrentCalendar];
NSDateComponents *dateComponent = [[NSDateComponents alloc]init];
[dateComponent setYear:10];
NSLog(@"%@",[calender dateByAddingComponents:dateComponent toDate:[NSDate             dateWithTimeIntervalSinceNow:0] options:NSCalendarWrapComponents] );

- dateFromComponents:返回一个新的 NSDate 对象，表示从给定组件计算的绝对时间。

NSCalendar *calender = [NSCalendar autoupdatingCurrentCalendar];
NSDateComponents *dateComponent = [[NSDateComponents alloc]init];
[dateComponent setYear:2020];
NSLog(@"%@",[calender dateFromComponents:dateComponent]);