试试下面的方法:

    NSString *birthday = @"06/15/1977";
    NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
    [formatter setDateFormat:@"MM/dd/yyyy"];
    NSDate *date = [formatter dateFromString:birthday];
    if(date!=nil) {
        NSInteger age = [date timeIntervalSinceNow]/31556926;
        NSDateComponents *components = [[NSCalendar currentCalendar] components:NSCalendarUnitDay | NSCalendarUnitMonth | NSCalendarUnitYear fromDate:date];
        NSInteger day = [components day];
        NSInteger month = [components month];
        NSInteger year = [components year];

        NSLog(@"Day:%d Month:%d Year:%d Age:%d",day,month,year,age);
    }
    [formatter release];

只是重新描述一下Itai的优秀(并且工作!)代码，下面是一个示例助手类，它返回给定NSDate变量的年份值。

如您所见，修改这段代码以获得月或日是很容易的。

+(int)getYear:(NSDate*)date
{
    NSDateComponents *components = [[NSCalendar currentCalendar] components:NSDayCalendarUnit | NSMonthCalendarUnit | NSYearCalendarUnit fromDate:date];

    int year = [components year];
    int month = [components month];
    int day = [components day];

    return year;
}

(我真不敢相信，在2013年，我们还得自己编写这样的基本iOS日期函数……)

还有一件事:永远不要使用<和>来比较两个NSDate值。

XCode很乐意接受这样的代码(没有任何错误或警告)，但其结果是一个彩票。你必须使用"compare"函数来比较nsdate:

if ([date1 compare:date2] == NSOrderedDescending) {
    // date1 is greater than date2        
}

    NSDate *currDate = [NSDate date];
    NSCalendar*       calendar = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];
    NSDateComponents* components = [calendar components:NSDayCalendarUnit|NSMonthCalendarUnit|NSYearCalendarUnit fromDate:currDate];
    NSInteger         day = [components day];
    NSInteger         month = [components month];
    NSInteger         year = [components year];
    NSLog(@"%d/%d/%d", day, month, year);

要获得人类可读的字符串(日，月，年)，你可以这样做:

NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
[dateFormatter setDateStyle:NSDateFormatterMediumStyle];
NSString *string = [dateFormatter stringFromDate:dateEndDate];

试试下面的方法:

    NSString *birthday = @"06/15/1977";
    NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
    [formatter setDateFormat:@"MM/dd/yyyy"];
    NSDate *date = [formatter dateFromString:birthday];
    if(date!=nil) {
        NSInteger age = [date timeIntervalSinceNow]/31556926;
        NSDateComponents *components = [[NSCalendar currentCalendar] components:NSCalendarUnitDay | NSCalendarUnitMonth | NSCalendarUnitYear fromDate:date];
        NSInteger day = [components day];
        NSInteger month = [components month];
        NSInteger year = [components year];

        NSLog(@"Day:%d Month:%d Year:%d Age:%d",day,month,year,age);
    }
    [formatter release];

因为这显然是我最喜欢的答案，我将试着编辑它，以包含更多的信息。

Despite its name, NSDate in and of itself simply marks a point in machine time, not a date. There's no correlation between the point in time specified by an NSDate and a year, month, or day. For that, you have to refer to a calendar. Any given point in time will return different date information based on what calendar you're looking at (dates are not the same in both the Gregorian and Jewish calendars, for instance), and while the Gregorian calendar is the most widely used calendar in the world - I'm assuming - we're a little biased that NSDate should always use it. NSDate, luckily, is far more bipartisan.

获取日期和时间将必须通过NSCalendar，正如你提到的，但有一个更简单的方法来做它:

NSDateComponents *components = [[NSCalendar currentCalendar] components:NSCalendarUnitDay | NSCalendarUnitMonth | NSCalendarUnitYear fromDate:[NSDate date]];

它生成一个NSDateComponents对象，其中包含来自当前系统日历的日、月和年。(注意:这不一定是当前用户指定的日历，只是默认的系统日历。)

当然，如果你使用不同的日历或日期，你可以很容易地更改它。可用日历和日历单元的列表可以在NSCalendar类引用中找到。更多关于NSDateComponents的信息可以在NSDateComponents类参考中找到。

作为参考，从NSDateComponents中访问单个组件相当简单:

NSInteger day = [components day];
NSInteger month = [components month];
NSInteger year = [components year];

You just have to be mindful: NSDateComponents won't contain valid information for any fields you ask for unless you generated them with that valid information (i.e. request NSCalendar to provide that information with NSCalendarUnits). NSDateComponents contain no reference information in and of themselves - they're just simple structures that hold numbers for you to access. If you want to also get an era, for instance, out of NSDateComponents, you'll have to feed the generator method from NSCalendar with the NSCalendarUnitEra flag.