Q:

conversion from NSTimeInterval to hour,minutes,seconds,milliseconds in swift

My code is here:
func stringFromTimeInterval(interval:NSTimeInterval) -> NSString {

    var ti = NSInteger(interval)
    var ms = ti * 1000
    var seconds = ti % 60
    var minutes = (ti / 60) % 60
    var hours = (ti / 3600)

      return NSString(format: "%0.2d:%0.2d:%0.2d",hours,minutes,seconds,ms)
}

in output the milliseconds give wrong result.Please give an idea how to find milliseconds correctly.

A:

Swift supports remainder calculations on floating-point numbers, so we can use % 1. 
var ms = Int((interval % 1) * 1000)

as in: 
func stringFromTimeInterval(interval: TimeInterval) -> NSString {

  let ti = NSInteger(interval)

  let ms = Int((interval % 1) * 1000)

  let seconds = ti % 60
  let minutes = (ti / 60) % 60
  let hours = (ti / 3600)

  return NSString(format: "%0.2d:%0.2d:%0.2d.%0.3d",hours,minutes,seconds,ms)
}

result:
stringFromTimeInterval(12345.67)                   "03:25:45.670"

Swift 4:
extension TimeInterval{

        func stringFromTimeInterval() -> String {

            let time = NSInteger(self)

            let ms = Int((self.truncatingRemainder(dividingBy: 1)) * 1000)
            let seconds = time % 60
            let minutes = (time / 60) % 60
            let hours = (time / 3600)

            return String(format: "%0.2d:%0.2d:%0.2d.%0.3d",hours,minutes,seconds,ms)

        }
    }

Use:
self.timeLabel.text = player.duration.stringFromTimeInterval()

A:

SWIFT 3 Extension 
I think this way is a easier to see where each piece comes from so you can more easily modify it to your needs
extension TimeInterval {
    private var milliseconds: Int {
        return Int((truncatingRemainder(dividingBy: 1)) * 1000)
    } 

    private var seconds: Int {
        return Int(self) % 60
    } 

    private var minutes: Int {
        return (Int(self) / 60 ) % 60
    } 

    private var hours: Int {
        return Int(self) / 3600
    } 

    var stringTime: String {
        if hours != 0 {
            return "\(hours)h \(minutes)m \(seconds)s"
        } else if minutes != 0 {
            return "\(minutes)m \(seconds)s"
        } else if milliseconds != 0 {
            return "\(seconds)s \(milliseconds)ms"
        } else {
            return "\(seconds)s"
        }
    }
}

A:

Equivalent in Objective-C, based on the @matthias-bauch answer.
+ (NSString *)stringFromTimeInterval:(NSTimeInterval)timeInterval
{
    NSInteger interval = timeInterval;
    NSInteger ms = (fmod(timeInterval, 1) * 1000);
    long seconds = interval % 60;
    long minutes = (interval / 60) % 60;
    long hours = (interval / 3600);

    return [NSString stringWithFormat:@"%0.2ld:%0.2ld:%0.2ld,%0.3ld", hours, minutes, seconds, (long)ms];
}

