Xcode time difference in days, hours, minutes and seconds - xcode

Question

First of all: I want to say happy new year to everybody reading this!! May 2015 be a great year for all of us :-).
I'm busy with making a function which calculates the time difference between two dates. To be more precise: the time between a time and date given and the current time and date.
So the user selects a date in the past and then the program shows the time difference between the given date and todays date in a timer like so: "hh:mm:ss"
It works okay and updates every second when i select a time of todays date (01-01-2015 10:00:00), but when selecting a date and time in the past (31-12-2014 17:00:00) and compare it to todays date where the time is earlier than yesterday (01-01-2015 14:01:01), it gives me a negative time like a sort of countdown timer: -2:-59:-59.
But i want it to show the opposite of it: 21:01:01 and if possible if it exceeds the 24:00:00, just count on. For example 25:12:39.
This is the code that calculates the difference:
NSDateFormatter *df = [[NSDateFormatter alloc] init];
[df setDateFormat:#"dd-MM-YYYY HH:mm:ss"];
NSDate *date1 = [df dateFromString:[NSString stringWithFormat:#"30-12-2014 %#", startedTime]];
NSDate *date2 = [df dateFromString:[NSString stringWithFormat:#"31-12-2014 %#", [self getCurrentTime]]];
NSTimeInterval interval = [date2 timeIntervalSinceDate:date1];
int hours = (int)interval / 3600; // integer division to get the hours part
int minutes = (interval - (hours*3600)) / 60; // interval minus hours part (in seconds) divided by 60 yields minutes
int seconds = (interval - (hours*3600) - (minutes*60)); // interval minus hours part (in seconds) divided by 60 yields minutes
NSString *timeDiff = [NSString stringWithFormat:#"%02d:%02d:%02d", hours, minutes, seconds];
_workingTime.text = [NSString stringWithFormat:#"%#",timeDiff];
Can someone please help?

Answer 1

[df setDateFormat:#"dd-MM-yyyy hh:mm:ss"];
Try after this change of the format string!
And this.. finally.
NSTimeInterval interval = [date2 timeIntervalSinceDate:date1];
if( interval < 0 ) {
interval = [date1 timeIntervalSinceDate:date2];
}
More about date formats here