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];
}