AVPlayer currentTime update for a UISlider when ViewController load - ios

Question

I'm playing songs in AVPlayer. I have created a separate view controller for my media player and initialization, and all the methods that I'm using for the player (play, pause, repeat, shuffle) are there in the same view controller.
I update a slider like this:
[NSTimer scheduledTimerWithTimeInterval:1.0 target:self selector:#selector(sliderUpdate:) userInfo:nil repeats:YES];`
- (void) sliderUpdate:(id) sender{
int currentTime = (int)((song.player.currentTime.value)/song.player.currentTime.timescale);
slider.value=currentTime;
NSLog(#"%i",currentTime);
song.currentTime=currentTime;
int currentPoint=(int)((song.player.currentTime.value)/song.player.currentTime.timescale);
int pointMins=(int)(currentPoint/60);
int pointSec=(int)(currentPoint%60);
NSString *strMinlabel=[NSString stringWithFormat:#"%02d:%02d",pointMins,pointSec];
lblSlidermin.text=strMinlabel;
song.strslidermin=strMinlabel;
}
Once I'm going out of the viewcontroller and when come again, song is playing but the problem is slider is not updating. So I created a singleton class to assign currently playing song details. Also inside the slider update I asigned playerCurrentTime (slidercurrent value) for a singleton class variable. And my viewdidload method I assigned like this:
if (song.isPlaying==NO) {
[self prePlaySong];
}else{
lblAlbum.text=song.currentAlbum;
lblArtist.text=song.currentArtist;
lblSong.text=song.currentSong;
slider.value=song.currentTime;
slider.maximumValue=song.sliderMax;
slider.minimumValue=song.sliderMin;
imgSong.image=song.songImage;
[btnMiddle setBackgroundImage:[UIImage imageNamed:#"pause.png"] forState:UIControlStateNormal];
}
but slider is not getting updated. Why is that and how I can solve this problem?

Answer 1

You should not use a timer for this, AVPlayer provides an API you observe the time.
Register an observer (e.g. in viewWillAppear) like this:
CMTime interval = CMTimeMakeWithSeconds(1.0, NSEC_PER_SEC); // 1 second
self.playbackTimeObserver =
[self.player addPeriodicTimeObserverForInterval:interval
queue:NULL usingBlock:^(CMTime time) {
// update slider value here...
}];
To unregister the observer (e.g. in viewDidDisappear), do:
[self.player removeTimeObserver:self.playbackTimeObserver];
Hope that helps.

Answer 2

Swift 3 version.
Register an observer:
// Invoke callback every second
let interval = CMTime(seconds:1.0, preferredTimescale: CMTimeScale(NSEC_PER_SEC))
// Queue on which to invoke the callback
let mainQueue = DispatchQueue.main
// Keep the reference to remove
self.playerObserver = player.addPeriodicTimeObserver(forInterval: interval, queue: mainQueue) { time in
print(time)
}
Remove an obserber:
if let observer = self.playerObserver {
self.player.removeTimeObserver(observer)
self.playerObserver = nil
}