No need to use NSDateFormatter or anything else than division and modulo. NSTimeInterval is just a double containing seconds.

Swift

func stringFromTimeInterval(interval: NSTimeInterval) -> String {
let interval = Int(interval)
let seconds = interval % 60
let minutes = (interval / 60) % 60
let hours = (interval / 3600)
return String(format: "%02d:%02d:%02d", hours, minutes, seconds)
}

Objective-C

- (NSString *)stringFromTimeInterval:(NSTimeInterval)interval {
NSInteger ti = (NSInteger)interval;
NSInteger seconds = ti % 60;
NSInteger minutes = (ti / 60) % 60;
NSInteger hours = (ti / 3600);
return [NSString stringWithFormat:@"%02ld:%02ld:%02ld", (long)hours, (long)minutes, (long)seconds];
}

Some extra lines of code, but I feel using NSDateComponents will give a more precise value.

- (NSString *)getTimeRepresentationFromDate:(NSDate *)iDate withTimeInterval:(NSTimeInterval)iTimeInterval {
NSString *aReturnValue = nil;
NSDate *aNewDate = [iDate dateByAddingTimeInterval:iTimeInterval];


unsigned int theUnits = NSHourCalendarUnit | NSMinuteCalendarUnit | NSSecondCalendarUnit;
NSCalendar *aCalender = [NSCalendar currentCalendar];
NSDateComponents *aDateComponents = [aCalender components:theUnits fromDate:iDate toDate:aNewDate options:0];


aReturnValue = [NSString stringWithFormat:@"%d:%d:%d", [aDateComponents hour], [aDateComponents minute], [aDateComponents second]];


return aReturnValue;
}

NSTimeInterval ti = 3667;
double hours = floor(ti / 60 / 60);
double minutes = floor((ti - (hours * 60 * 60)) / 60);
double seconds = floor(ti - (hours * 60 * 60) - (minutes * 60));

On iOS 8, use NSDateComponentsFormatter.

NSDateComponentsFormatter *dateComponentsFormatter = [[NSDateComponentsFormatter alloc] init];
NSLog(@"%@", [dateComponentsFormatter stringFromTimeInterval:200.0]);

outputs "3:20".

NSDateComponentsFormatter *dateComponentsFormatter = [[NSDateComponentsFormatter alloc] init];
dateComponentsFormatter.zeroFormattingBehavior = NSDateComponentsFormatterZeroFormattingBehaviorPad;
dateComponentsFormatter.allowedUnits = (NSCalendarUnitHour | NSCalendarUnitMinute | NSCalendarUnitSecond);
NSLog(@"%@", [dateComponentsFormatter stringFromTimeInterval:200.0]);

outputs "0:03:20".

To "extend" Matthias Bauch's suggestion, in Swift I would make this a computed property of NSTimeInterval:

extension NSTimeInterval {
var stringValue: String {
let interval = Int(self)
let seconds = interval % 60
let minutes = (interval / 60) % 60
let hours = (interval / 3600)
return String(format: "%02d:%02d:%02d", hours, minutes, seconds)
}
}

The advantage of this is it's attached to the NSTimeInterval type, not your view controller or wherever else you put that function. To use you'd go something like:

let timeInterval = NSDate().timeIntervalSinceDate(start)
self.elapsedTimeLabel.text = timeInterval.stringValue

In Swift 2, iOS 8+. This makes sure we only show hour when necessary

func format(duration: NSTimeInterval) -> String {
let formatter = NSDateComponentsFormatter()
formatter.zeroFormattingBehavior = .Pad


if duration >= 3600 {
formatter.allowedUnits = [.Hour, .Minute, .Second]
} else {
formatter.allowedUnits = [.Minute, .Second]
}


return formatter.stringFromTimeInterval(duration) ?? ""
}

So you have

print(format(12)) // 0:12
print(format(65)) // 1:05
print(format(1750)) // 29:10
print(format(3890)) // 1:04:50
print(format(45720)) // 12:42:00

Swift 3 version of onmyway133's answer:

import Foundation


func format(_ duration: TimeInterval) -> String {
let formatter = DateComponentsFormatter()
formatter.zeroFormattingBehavior = .pad
formatter.allowedUnits = [.minute, .second]


if duration >= 3600 {
formatter.allowedUnits.insert(.hour)
}


return formatter.string(from: duration)!
}




print(format(12)) // 0:12
print(format(65)) // 1:05
print(format(1750)) // 29:10
print(format(3890)) // 1:04:50
print(format(45720)) // 12:42:00

Based on answer by @onmyway133 here is the Swift 4 version:

func format(duration: TimeInterval) -> String {
let formatter = DateComponentsFormatter()
formatter.zeroFormattingBehavior = .pad


if duration >= 3600 {
formatter.allowedUnits = [.hour, .minute, .second];
} else {
formatter.allowedUnits = [.minute, .second];
}


return formatter.string(from: duration) ?? "";
}

straight from apple docs: in h file:

 @property(strong,nonatomic)NSDateComponentsFormatter *timerFormatter;

in m file

@synthesize timerFormatter;


- (void)viewDidLoad {
[super viewDidLoad];
NSDateComponentsFormatter *timerFormatter = [[NSDateComponentsFormatter alloc] init];
timerFormatter.unitsStyle = NSDateComponentsFormatterUnitsStylePositional;
//10:59 Positional THIS ONE DOES NOT SEEM TO WORK iOS<9 WHEN <1Minute JUST SHOWS 01, 10m 59s Abbreviated, 10min 59sec Short, 10minutes 59seconds Full ...
timerFormatter.allowedUnits = NSCalendarUnitHour|NSCalendarUnitMinute|NSCalendarUnitSecond;
}

whereever you need to convert your NSTimeInterval timeInterval to hh:mm:ss string, do this:

NSString *txt=[timerFormatter stringFromTimeInterval:timeInterval];

I guess, the timer fraction should be ceiled out. As Matthias' code was creating that issue in seconds, I use the following slightly modified from that of Matthias

    - (NSString *)stringFromTimeInterval:(NSTimeInterval)interval {
int ti = (int) ceil(interval);
int seconds = ti % 60;
int minutes = (ti / 60) % 60;
int hours = (ti / 3600);
return [NSString stringWithFormat:@"%02d:%02d:%02d",hours, minutes, seconds];
}

Swift 4

DateComponentsFormatter().string(from: <# TimeInterval #>)

ex:

DateComponentsFormatter().string(from: 59.0)

Objective C version of onmyway133's answer

- (NSString*) formatTimeInterval:(NSTimeInterval) timeInterval {


NSDateComponentsFormatter *formatter = [[NSDateComponentsFormatter alloc] init];


formatter.zeroFormattingBehavior = NSDateComponentsFormatterZeroFormattingBehaviorPad;


if (timeInterval > 3600) {
formatter.allowedUnits = NSCalendarUnitHour | NSCalendarUnitMinute | NSCalendarUnitSecond;
} else {
formatter.allowedUnits = NSCalendarUnitMinute | NSCalendarUnitSecond;
}


return [formatter stringFromTimeInterval:timeInterval];
}