IOS 获取当前系统时间的年、月、日、小时、分、秒

NSCalendar *calendar = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];
NSDate *now;
NSDateComponents *comps = [[NSDateComponents alloc] init];
NSInteger unitFlags = NSYearCalendarUnit | NSMonthCalendarUnit | NSDayCalendarUnit | NSWeekdayCalendarUnit | 
                                         NSHourCalendarUnit | NSMinuteCalendarUnit | NSSecondCalendarUnit;
now=[NSDate date];
comps = [calendar components:unitFlags fromDate:now];
week = [comps weekday];    
month = [comps month];
day = [comps day];
hour = [comps hour];
min = [comps minute];
sec = [comps second];

//Week:
1 －－星期天
2－－星期一
3－－星期二
4－－星期三
5－－星期四
6－－星期五
7－－星期六