获取当前时间（方便计算年龄等..）

呀嘞呀嘞 好久不写 之前准备毕业 之后又忙着APP改版 所以就...

first step: 获取当前的时间 格式为:NSDate

NSDate *date = [NSDate date];

不要告诉我你不会这句..

second step:转换成字符串：这时候就需要设置需要转换的格式了

NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
formatter.dateFormat = @"YYYY MM dd"; // 这个时间展示格式你随意
NSString *str = [formatter stringFromDate:date]; // date转字符串
NSDate *date = [formatter dateFromString:str]; // 字符串转date

啊 对了这是时分秒：hh:mm:ss 不用谢~
这时候要是想要计算年龄 ,如下：

- (NSInteger)agesWithBirthday:(NSDate *)birthdayDate {
    if (birthdayDate) {
        NSDate *currentDate = [NSDate date];
        NSDateComponents *components = [[NSCalendar currentCalendar] components:(NSCalendarUnitYear | NSCalendarUnitMonth | NSCalendarUnitDay | NSCalendarUnitWeekOfYear |  NSCalendarUnitHour | NSCalendarUnitMinute | NSCalendarUnitSecond | NSCalendarUnitWeekday | NSCalendarUnitWeekdayOrdinal) fromDate:currentDate];

        NSDateComponents *birthComponents = [[NSCalendar currentCalendar] components:(NSCalendarUnitYear | NSCalendarUnitMonth | NSCalendarUnitDay | NSCalendarUnitWeekOfYear |  NSCalendarUnitHour | NSCalendarUnitMinute | NSCalendarUnitSecond | NSCalendarUnitWeekday | NSCalendarUnitWeekdayOrdinal) fromDate:birthdayDate];

        NSInteger ages = components.year - birthComponents.year;
        if (components.month < birthComponents.month) {
            ages --;
        }
        if (components.month == birthComponents.month) {
            if (components.day < birthComponents.day) {
                ages --;
            }
        }
        NSLog(@"年龄是：%ld", ages);
        return ages;
    }
    return -1;
}

调用：

NSArray *array = @[@"19980101", @"19980111", @"19980903", @"19981003", @"19700901", @"19701001", @"19700903", @"19700801"];
    NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
    formatter.dateFormat = @"YYYYMMdd";
    for (int i = 0; i < array.count; i++) {
        NSString *SFZstr = array[i];
        NSDate *date = [formatter dateFromString:SFZstr];
        [self agesWithBirthday:date];
    }

好啦 就是这样 有问题 请指正 谢谢~