iOS开发之获取当前日期的具体年、月、日及星期

有时候需要获取当前时间的详细日期：

NSDate *date = [NSDate date];
    NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
    [formatter setDateFormat:@"yyyy-MM-dd HH:mm:ss"];
    //获取当前时间日期展示字符串 如：2019-05-23-13:58:59
    NSString *str = [formatter stringFromDate:date];

    //下面是单独获取每项的值
    NSCalendar *calendar = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];
    NSDateComponents *comps = [[NSDateComponents alloc] init];
    NSInteger unitFlags = NSYearCalendarUnit |NSMonthCalendarUnit |NSDayCalendarUnit |NSWeekdayCalendarUnit |NSHourCalendarUnit |NSMinuteCalendarUnit |NSSecondCalendarUnit;
    comps = [calendar components:unitFlags fromDate:date];
    //星期 注意星期是从周日开始计算
    int week = [comps weekday];
    //年
    int year=[comps year];
    //月
    int month = [comps month];
    //日
    int day = [comps day];
    //时
    int hour = [comps hour];
    //分
    int minute = [comps minute];
    //秒
    int second = [comps second];