ReaderViewController.swift

class ReaderViewController: UIViewController {

    @IBOutlet weak var videoPreview: UIView!
    private var videoLayer: CALayer!
    
    var codeReader: CodeReader!

    override func viewDidLoad() {
        videoLayer = codeReader.videoPreview
        videoPreview.layer.addSublayer(videoLayer)
    }

    override func viewDidLayoutSubviews() {
        super.viewDidLayoutSubviews()
        videoLayer.frame = videoPreview.bounds
    }

    override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)
        codeReader.startReading { [weak self] (code) in
            self?.fetchCard(for: code)
        }
    }

    override func viewWillDisappear(_ animated: Bool) {
        super.viewWillDisappear(animated)
        codeReader.stopReading()
    }

}