获取系统时间

        NSDate* now = [NSDatedate];

       NSCalendar *calendar = [[NSCalendaralloc] initWithCalendarIdentifier:NSGregorianCalendar];

       NSInteger unitFlags =NSYearCalendarUnit | NSMonthCalendarUnit |NSDayCalendarUnit | NSWeekdayCalendarUnit |

       NSHourCalendarUnit | NSMinuteCalendarUnit |NSSecondCalendarUnit;

        NSDateComponents *comps = [calendar components:unitFlagsfromDate:now];

        int year = [comps year];

        int month = [comps month];

        int day = [comps day];

        int hour = [comps hour];

        int min = [comps minute];

        int sec = [comps second]; 

    

        NSString * strtime = [NSString stringWithFormat:@"%d-%d-%d %d:%d:%d", year, month,day,hour,min,sec];