获取当前时间

        NSDate *now = [NSDate date];
        NSLog(@”now date is: %@”, now);

        NSCalendar *calendar = [NSCalendar currentCalendar];
        NSUInteger unitFlags = NSYearCalendarUnit | NSMonthCalendarUnit | NSDayCalendarUnit | NSHourCalendarUnit | NSMinuteCalendarUnit | NSSecondCalendarUnit;
        NSDateComponents *dateComponent = [calendar components:unitFlags fromDate:now];

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

        NSLog(@”year is: %d”, year);
        NSLog(@”month is: %d”, month);
        NSLog(@”day is: %d”, day);
        NSLog(@”hour is: %d”, hour);
        NSLog(@”minute is: %d”, minute);
        NSLog(@”second is: %d”, second);

计算年龄

第一种仅仅得出年份差的年龄

    //计算年龄
    NSString *birth = @"1993-10-30";
    NSDateFormatter *dateFormatter = [[NSDateFormatter alloc]init];
    [dateFormatter setDateFormat:@"yyyy-MM-dd"];
    //生日
    NSDate *birthDay = [dateFormatter dateFromString:birth];
    //当前时间
    NSString *currentDateStr = [dateFormatter stringFromDate:[NSDate date]];
    NSDate *currentDate = [dateFormatter dateFromString:currentDateStr];
    NSLog(@"currentDate %@ birthDay %@",currentDateStr,birth);
    NSTimeInterval time=[currentDate timeIntervalSinceDate:birthDay];
    int age = ((int)time)/(3600*24*365);
    NSLog(@"year %d",age);

另外一种得出详细到天的年龄

NSCalendar *calendar = [NSCalendar currentCalendar];//定义一个NSCalendar对象

    NSDate *nowDate = [NSDate date];

    NSString *birth = @"1900-10-30";
    NSDateFormatter *dateFormatter = [[NSDateFormatter alloc]init];
    [dateFormatter setDateFormat:@"yyyy-MM-dd"];
    //生日
    NSDate *birthDay = [dateFormatter dateFromString:birth];

    //用来得到详细的时差
    unsigned int unitFlags = NSYearCalendarUnit | NSMonthCalendarUnit | NSDayCalendarUnit | NSHourCalendarUnit | NSMinuteCalendarUnit | NSSecondCalendarUnit;
    NSDateComponents *date = [calendar components:unitFlags fromDate:birthDay toDate:nowDate options:0];

    if([date year] >0)
    {
        NSLog(@"%@",[NSString stringWithFormat:(@"%ld岁%ld月%ld天"),(long)[date year],(long)[date month],(long)[date day]]) ;
    }
    else if([date month] >0)
    {
        NSLog(@"%@",[NSString stringWithFormat:(@"%ld月%ld天"),(long)[date month],(long)[date day]]);
    }
    else if([date day]>0){
        NSLog(@"%@",[NSString stringWithFormat:(@"%ld天"),(long)[date day]]);
    }
    else {
       NSLog(@"0天");
    }

字符串、日期、Int转换

此项參考：http://blog.csdn.net/tt5267621/article/details/7720434

1、字符串转换为日期

NSDateFormatter* dateFormat = [[NSDateFormatter alloc] init];//实例化一个NSDateFormatter对象

[dateFormat setDateFormat:@"yyyy-MM-dd HH:mm:ss"];//设定时间格式,这里能够设置成自己须要的格式

NSDate *date =[dateFormat dateFromString:@"1980-01-01 00:00:01"];

2、日期转换为字符串

NSDateFormatter* dateFormat = [[NSDateFormatter alloc] init];//实例化一个NSDateFormatter对象

[dateFormat setDateFormat:@"yyyy-MM-dd HH:mm:ss"];//设定时间格式,这里能够设置成自己须要的格式

NSString *currentDateStr = [dateFormat stringFromDate:[NSDate date]];

3、字符串转int

Convert NSString to int

NSString *aNumberString = @"123";

int i = [aNumberString intValue];

4、int转字符串

Convert int to NSString

int aNumber = 123;

NSString *aString = [NSString stringWithFormat:@"%d", aNumber];