UISlider jumps when updating for AVPlayer

Question

I try to implement simple player with UISlider to indicate at what time is current audio file.

In code I have added two observers:

    slider.rx.value.subscribe(onNext: { value in
        let totalTime = Float(CMTimeGetSeconds(self.player.currentItem!.duration))
        let seconds = value * totalTime
        let time = CMTime(seconds: Double(seconds), preferredTimescale: CMTimeScale(NSEC_PER_SEC))
        self.player.seek(to: time)
        }).disposed(by: bag)
    let interval = CMTime(seconds: 0.1, preferredTimescale: CMTimeScale(NSEC_PER_SEC))
    player.addPeriodicTimeObserver(forInterval: interval, queue: nil) { [weak self] time in
        self?.updateSlider(with: time)
    }

with one private function:

private func updateSlider(with time: CMTime) {
    let currentTime = CMTimeGetSeconds(time)
    var totalTime = CMTimeGetSeconds(player.currentItem!.duration)
    if totalTime.isNaN {
        totalTime = 0
    }
    startLabel.text = Int(currentTime).descriptiveDuration
    endLabel.text = Int(totalTime).descriptiveDuration
    slider.value = Float(currentTime / totalTime)
}

When audio plays, everything is fine and slider is pretty much updated. The problem occurs when I try to move slider manually while audio is playing, then it jumps. Why?

UPDATE:

I know why actually. Because I update it twice: manually and from player observer, but how to prevent from this behaviour? I have no idea;) please, help.

Answer 1

One simple way to go about this would be to prevent addPeriodicTimeObserver from calling self?.updateSlider(with: time) when the slider is being touched.

This can be determined via the UISliders isTracking property:

isTracking

A Boolean value indicating whether the control is currently tracking touch events.

While tracking of a touch event is in progress, the control sets the value of this property to true. When tracking ends or is cancelled for any reason, it sets this property to false.

_{Ref: https://developer.apple.com/documentation/uikit/uicontrol/1618210-istracking}

This is present in all UIControl elements which you can use in this way:

player.addPeriodicTimeObserver(forInterval: interval, queue: nil) { [weak self] time in
    //check if slider is being touched/tracked
    guard self?.slider.isTracking == false else { return }

    //if slider is not being touched, then update the slider from here
    self?.updateSlider(with: time)
}

---

Generic Example:

@IBOutlet var slider: UISlider!
//...
func startSlider() {
    slider.value = 0
    slider.maximumValue = 10

    Timer.scheduledTimer(withTimeInterval: 0.1, repeats: true) { [weak self] (timer) in
        print("Slider at: \(self?.slider.value)")
        guard self?.slider.isTracking == false else { return }
        self?.updateSlider(to: self!.slider.value + 0.1)
    }
}

private func updateSlider(to value: Float) {
    slider.value = value
}

---

_{I'm sure there are other (better) ways out there but I haven't done much in RxSwift (yet).
I hope this is good enough for now.}