将框架设置为UIView的框架时未渲染AVPlayerLayer

Question

我遇到了一个奇怪的问题，在下面的代码中，如果我将playerLayer.frame设置为view.frame，它仍然会加载视频，只是显然它溢出到playerContainer之外。

但是如果我将playerLayer.frame设置为playerContainer.frame，这是有道理的，因为我正在将subLayer添加到playerContainer中，它根本不会呈现。

var player: AVPlayer?
var playerLayer: AVPlayerLayer?

let playerContainer: UIView = {
    let view = UIView()
    return view
}()

let randomizeButton: UIButton = {
    let button = UIButton()
    button.setTitle("Change video", for: .normal)
    button.backgroundColor = UIColor.black
    return button
}()

override func viewDidLoad() {
    super.viewDidLoad()

    view.backgroundColor = UIColor.white

    setupVideoPlayer()
    setupRandomizeButton()

}

private func setupVideoPlayer() {
    view.addSubviewUsingAutoLayout(playerContainer)
    playerContainer.topAnchor.constrain(to: view.topAnchor)
    playerContainer.leadingAnchor.constrain(to: view.leadingAnchor)
    playerContainer.trailingAnchor.constrain(to: view.trailingAnchor)
    playerContainer.heightAnchor.constrain(to: view.frame.width)
    playerContainer.backgroundColor = UIColor.gray

    if let url = URL(string: videoURLArray[0]) {
        player = AVPlayer(url: url)
    }
    playerLayer = AVPlayerLayer(player: player)
    //playerLayer?.videoGravity = AVLayerVideoGravity.resizeAspectFill
    playerLayer?.frame = view.frame

    playerContainer.layer.addSublayer(playerLayer!)

    player?.play()
}