Difference between two NSDate objects -- Result also a NSDate

I have two NSDate objects and I want the difference between the two and the result should again be a NSDate object. Any idea how to achieve this?

Here, I am trying to address a unique problem where I have to find out the elapsed time and then localize the elapsed time. I can localize it if I have the elapsed time in NSDate object. So thought of creating a NSDate object which has its time component same as time interval between the two dates so that I could use NSDateFormatter to localize it.

NSDate represents an instance in time, so it doesn't make sense to represent an interval of time as an NSDate. What you want is NSDateComponents:

NSDate *dateA;
NSDate *dateB;

NSCalendar *calendar = [[NSCalendar alloc] initWithCalendarIdentifier:NSCalendarIdentifierGregorian];
NSDateComponents *components = [calendar components:NSCalendarUnitYear|NSCalendarUnitMonth|NSCalendarUnitDay
                                           fromDate:dateA
                                             toDate:dateB
                                            options:0];

NSLog(@"Difference in date components: %i/%i/%i", components.day, components.month, components.year);

If you subtract 12/12/2001 from 05/05/2002 what will be the date? The chronological distance between two dates can't be a date, it's alway some kind of interval. You can use timeIntervalSinceDate: to calculate the interval.

To localize you can try the following steps:

• You can use the NSCalendar with dateFromComponents: passing in a NSDateComponents.

• To break down a timeInterval into NSDateComponents look at How do I break down an NSTimeInterval into year, months, days, hours, minutes and seconds on iPhone?.

• Finally use the NSDateFormatter and initWithDateFormat:allowNaturalLanguage: to get your localized string. The Date Format String Syntax shows the different placeholders.

From NSDate class reference, you have instance methods to do these -

1. How to compare two NSDate variables? Ans: isEqualToDate:
2. How to find difference between two NSDate variables? Ans: timeIntervalSinceDate:
3. How to get each separate value of minute, hours and days from NSDate variable? links

You can calculate the time interval between two dates using NSDate's timeIntervalSinceDate:, but it doesn't make any sense for you to represent a time interval as a date.

There is a easy way by using -compare: in NSDate:

NSDate *dateA = [NSDate dateWithTimeIntervalSinceNow:100];
NSDate *dateB = [NSDate dateWithTimeIntervalSinceNow:200];
NSDate *myDate = [NSDate dateWithTimeIntervalSinceNow:150];
NSArray *dateArray = [NSArray arrayWithObjects:dateA, dateB, myDate, nil];
NSArray *sortedArray = [dateArray sortedArrayUsingSelector:@selector(compare:)];
if ([myDate isEqualToDate:[sortedArray objectAtIndex:1]])
    NSLog(@"myDatea between dateA and dateB");