请记住,NSDate
对象始终按照GMT显示时间,而您从该日期中提取的组件会受到timeZoneWithName
部分的影响。
例如:
NSDate *today = [NSDate date];
NSLog(@"Today's date: %@",today);
unsigned hourAndMinuteFlags = NSHourCalendarUnit | NSMinuteCalendarUnit;
NSCalendar* calendar = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];
[calendar setTimeZone:[NSTimeZone timeZoneWithName:@"GMT"]];
NSDateComponents* travelDateTimeComponents = [calendar components:hourAndMinuteFlags fromDate:today];
NSString* hours = [NSString stringWithFormat:@"%02i", [travelDateTimeComponents hour]];
NSString* minutes = [NSString stringWithFormat:@"%02i", [travelDateTimeComponents minute]];
NSLog(@"Calendar: %@",calendar);
NSLog(@"Travel Components: %@",travelDateTimeComponents);
NSLog(@"Hours: %@",hours);
NSLog(@"Minutes: %@",minutes);
控制台输出:
[Session started at 2011-01-23 12:59:17 -0700.]
2011-01-23 12:59:19.755 testttt[5697:207] Today's date: 2011-01-23 19:59:19 +0000
2011-01-23 12:59:19.756 testttt[5697:207] Calendar: <__NSCFCalendar: 0x4b2ca70>
2011-01-23 12:59:19.757 testttt[5697:207] Travel Components: <NSDateComponents: 0x4b2de20>
2011-01-23 12:59:19.757 testttt[5697:207] Hours: 19
2011-01-23 12:59:19.758 testttt[5697:207] Minutes: 59
如果我们改变时区...
NSDate *today = [NSDate date];
NSLog(@"Today's date: %@",today);
unsigned hourAndMinuteFlags = NSHourCalendarUnit | NSMinuteCalendarUnit;
NSCalendar* calendar = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];
[calendar setTimeZone:[NSTimeZone timeZoneWithName:@"MST"]];
NSDateComponents* travelDateTimeComponents = [calendar components:hourAndMinuteFlags fromDate:today];
NSString* hours = [NSString stringWithFormat:@"%02i", [travelDateTimeComponents hour]];
NSString* minutes = [NSString stringWithFormat:@"%02i", [travelDateTimeComponents minute]];
NSLog(@"Calendar: %@",calendar);
NSLog(@"Travel Components: %@",travelDateTimeComponents);
NSLog(@"Hours: %@",hours);
NSLog(@"Minutes: %@",minutes);
输出:
2011-01-23 13:05:29.896 testttt[5723:207] Today's date: 2011-01-23 20:05:29 +0000
2011-01-23 13:05:29.897 testttt[5723:207] Calendar: <__NSCFCalendar: 0x4e10020>
2011-01-23 13:05:29.897 testttt[5723:207] Travel Components: <NSDateComponents: 0x4e0f6d0>
2011-01-23 13:05:29.898 testttt[5723:207] Hours: 13
2011-01-23 13:05:29.898 testttt[5723:207] Minutes: 05
注意本地的小时和分钟变化了,但是“今天的日期:”部分仍然反映着GMT。如果你问我,这有点误导程序员。