avplayer-debugging-1-isTracking-observer.swift

private var progressBarHighlightedObserver: NSKeyValueObservation?
    
private lazy var progressBar: UISlider = {
    let bar = UISlider()
    bar.minimumTrackTintColor = .red
    bar.maximumTrackTintColor = .white
    bar.value = 0.0
    bar.isContinuous = false
    bar.addTarget(self, action: #selector(handleSliderChange), for: .valueChanged)
    self.progressBarHighlightedObserver = bar.observe(\UISlider.isTracking, options: [.old, .new]) { (_, change) in
        if let newValue = change.newValue {
            self.didChangeProgressBarDragging?(newValue, bar.value)
        }
    }
    return bar
}()