UISlider alpha stuck at 0.5

Question

I have a UISlider inside a cell and I set its alpha to 1 but when the slider is displayed the alpha is stuck at 0.5. How do I change it?

lazy var videoSlider: UISlider = {
    let slider = UISlider()
    slider.translatesAutoresizingMaskIntoConstraints = false
    slider.minimumTrackTintColor = UIColor.orange
    slider.maximumTrackTintColor = UIColor.white
    slider.setThumbImage(UIImage(named: "sliderThumb"), for: .normal)
    slider.isEnabled = false
    slider.alpha = 1.0 // set at 1 here and never changed
    return slider
}()

I also tried:

override init(frame: CGRect) {
    super.init(frame: frame)
    backgroundColor = UIColor.black

    videoSlider.alpha = 0
    UIView.animate(withDuration: 0.33, animations: {
        self.videoSlider.alpha = 1
    })
}

this happens on the very first cell. There is only 1 cell on screen — Lance Samaria, Jun 09 '20 at 14:43
@PranavKasetti I just added **slider.isOpaque = true** after I set the alpha inside the closure, same result. Thanks though — Lance Samaria, Jun 09 '20 at 14:51
There are similar threads for this topic, you can take a look. https://stackoverflow.com/questions/4680473/uislider-ignores-alpha-when-set-to-0-5?rq=1 — Omer Faruk Ozturk, Jun 09 '20 at 14:52
@omerfarukozturk I saw that earlier but it only has no accepted answer and only 1 vote so I didn't;t have much faith in it. I'll try it though. Thanks — Lance Samaria, Jun 09 '20 at 14:53
@PranavKasetti The problem was the periodic time observer. For some strange reason it was resetting the slider's alpha to 0.5 every time there was an update. I just had to reset it to 1 on the main queue. Thanks for the help though :) — Lance Samaria, Jun 09 '20 at 15:08
Ok. Although in your periodic time observer the queue is already main, so you don't need to wrap it inside it again. :) — Pranav Kasetti, Jun 09 '20 at 15:10
I noticed that but for strange reason it didn't work when I added it in there without it. Definitely weird bug. — Lance Samaria, Jun 09 '20 at 15:11

Lance Samaria · Accepted Answer · 2020-06-09T15:54:29.467

It was the period time observer that was causing the problem. As the time progressed and the track moved along for some reason the slider color was getting reset to 0.5. To fix it I updated the alpha on the main queue.

timeObserverToken = player?.addPeriodicTimeObserver(forInterval: interval, queue: DispatchQueue.main, using: { [weak self](progressTime) in

    let seconds: Float64 = CMTimeGetSeconds(progressTime)

    if let duration = self?.player?.currentItem?.duration {

        let durationSeconds: Float64 = CMTimeGetSeconds(duration)

        // even though this is already happening on the main queue it didn't work without it
        DispatchQueue.main.async {
            self?.videoSlider.alpha = 1
        }

        self.videoSlider.value = Float(seconds / durationSeconds)
    }
})

UISlider alpha stuck at 0.5

1 Answers1