Problems formatting dates

Question

Here is the set up, I have a JSON feed I am using and I want to find the difference between two specific dates called posted_date and planned_expiration_date. They are in an odd format I so I thought I could truncate them down to just the date.I could then use NSTimeInterval to find the difference in seconds.

// Time Interval Left
NSDateFormatter *formatter = [[NSDateFormatter alloc]init];
NSString *startDate = [firstPerson objectForKey:@"posted_date"];
NSString *endDate = [firstPerson objectForKey:@"planned_expiration_date"];

//Ammend the strings to YYYY-MM-DD
[formatter setDateFormat:@"yyyy-mm-dd"];
int newlength = 9;
NSDate *startDateAmmended =[formatter dateFromString:[startDate substringFromIndex:newlength]];
NSDate *endDateAmmended = [formatter dateFromString:[endDate substringFromIndex:newlength]];

Here is the bit I'm not too sure about. The date appears something like this "2013-06-07T13:40:01Z" straight from the feed. I don't know how to deal with the T and Z chars in the date formatter method so I truncate the string with substringFromIndex to make it 10 chars and then attempted the following code.

//Difference in Date
NSTimeInterval *startDifference = [startDateAmmended timeIntervalSinceNow];
NSTimeInterval *endDifference = [endDateAmmended timeIntervalSinceNow];

NSTimeInterval timeDifferenceInSeconds = startDifference - endDifference;

I get the following error, .../JSONParser/ViewController.m:52:21: Initializing 'NSTimeInterval *' (aka 'double *') with an expression of incompatible type 'NSTimeInterval' (aka 'double') at the first two calls to NSTimeInterval.

I am sure I'm going wrong in a few places and I'm sure this isn't the easiest method of doing it. Could anyone recommend how I would fix this issue or an easier way to go about getting the differences between dates?

Maybe this could help you: http://stackoverflow.com/questions/6742771/how-to-calculate-difference-between-two-dates-without-using-any-ready-library-fu — Kauê Gimenes, Jun 07 '13 at 15:05

Rob · Accepted Answer · 2013-06-07T15:26:07.517

Your error comes from your lines that say:

NSTimeInterval *startDifference = [startDateAmmended timeIntervalSinceNow];
NSTimeInterval *endDifference = [endDateAmmended timeIntervalSinceNow];

They should be:

NSTimeInterval startDifference = [startDateAmmended timeIntervalSinceNow];
NSTimeInterval endDifference = [endDateAmmended timeIntervalSinceNow];

Or, more simply, don't define those two difference variables at all, and just use:

NSTimeInterval timeDifferenceInSeconds = [endDateAmmended timeIntervalSinceDate:startDateAmmended];

To calculate the difference between two ISO 8601 / RFC 3339 date strings, you can do:

NSDate *startDate = [self dateFromISO8601String:@"2013-06-01T16:27:35Z"];
NSDate *endDate   = [self dateFromISO8601String:@"2013-06-07T13:40:01Z"];

NSTimeInterval elapsed = [endDate timeIntervalSinceDate:startDate];
NSLog(@"Time elapsed (in seconds) is %.0f", elapsed);

where dateFromISO8601String is defined as:

- (NSDate *)dateFromISO8601String:(NSString *)string
{
    static NSDateFormatter *formatter = nil;
    if (formatter == nil)
    {
        formatter = [[NSDateFormatter alloc] init];
        NSLocale *enUSPOSIXLocale = [[NSLocale alloc] initWithLocaleIdentifier:@"en_US_POSIX"];
        formatter.locale = enUSPOSIXLocale;
        formatter.dateFormat = @"yyyy'-'MM'-'dd'T'HH':'mm':'ss'Z'";
        formatter.timeZone = [NSTimeZone timeZoneForSecondsFromGMT:0];
    }
    return [formatter dateFromString:string];
}

gitaarik · Answer 2 · 2013-06-07T15:13:51.903

1

You can get the difference in seconds between two NSDate objects like this:

double difference = [startDateAmmended timeIntervalSinceDate:endDateAmmended];

Note that with the substring operation you don't have the time, only the date, so the difference will be in seconds but with steps of whole days.

edited Jun 07 '13 at 15:13

answered Jun 07 '13 at 15:08

gitaarik

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Problems formatting dates

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