获取当前的年、月、日、小时、分钟、秒

NSDate *nowDate = [NSDate date];

NSCalendar *calendar = [NSCalendar currentCalendar];
NSUInteger unitFlags = NSYearCalendarUnit | 
                       NSMonthCalendarUnit | //月份
                       NSDayCalendarUnit | //日
                       NSHourCalendarUnit |  //小时
                       NSMinuteCalendarUnit |  //分钟
                       NSSecondCalendarUnit;  // 秒
NSDateComponents *dateComponent = [calendar components:unitFlags fromDate:nowDate];

NSInteger year = [dateComponent year];
NSInteger month = [dateComponent month];
NSInteger day = [dateComponent day];
NSInteger hour = [dateComponent hour];
NSInteger minute = [dateComponent minute];
NSInteger second = [dateComponent second];