Difference between two NSDate objects -- Result also a NSDate

Question

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.

The difference between any two arbitrarily selected dates is always 19th February 1986. :-) — Damien_The_Unbeliever, Apr 06 '11 at 07:22

Nick Forge · Accepted Answer · 2016-10-07T02:46:51.657

152

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);

edited Oct 07 '16 at 02:46

answered Apr 06 '11 at 07:26

Nick Forge

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As of iOS 8, the calendar components are now (for this example): `NSCalendarUnitYear|NSCalendarUnitMonth|NSCalendarUnitDay` – Aaron Ash Aug 30 '16 at 09:32
Thanks @AaronAsh, I've updated the answer to reflect the latest constant names. – Nick Forge Sep 01 '16 at 01:57
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In iOS 8 NSGregorianCalendar is deprecated. Replace with NSCalendarIdentifierGregorian – isaiasmac Oct 05 '16 at 21:21

score 18 · Answer 2 · edited May 23 '17 at 11:45

18

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.

edited May 23 '17 at 11:45

Community

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answered Apr 06 '11 at 07:08

Nick Weaver

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I understand this. But 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. – Abhinav Apr 06 '11 at 07:27
@Abhinav I understand, there is a second problem arising: What is a month? Some months have 31 days others have 30. To represent an interval with the term month is very precise. You have to take that into account. – Nick Weaver Apr 06 '11 at 07:49

score 7 · Answer 3 · edited Apr 22 '23 at 12:31

7

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

How to compare two NSDate variables? Ans: isEqualToDate:
How to find difference between two NSDate variables? Ans: timeIntervalSinceDate:

edited Apr 22 '23 at 12:31

Dharman

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answered Apr 06 '11 at 07:11

Jhaliya - Praveen Sharma

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score 4 · Answer 4 · answered Apr 06 '11 at 07:10

4

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.

answered Apr 06 '11 at 07:10

score 3 · Answer 5 · answered Jul 08 '12 at 14:24

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");

Difference between two NSDate objects -- Result also a NSDate

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