gistfile1.txt

class GradientView: UIView {
    override class var layerClass: AnyClass { CAGradientLayer.self }

    override init(frame: CGRect) {
        super.init(frame: frame)
        isOpaque = false
        if let gradient = self.layer as? CAGradientLayer {
            gradient.startPoint = .init(x: 0.5, y: 0)
            gradient.endPoint = .init(x: 0.5, y: 1)
            //gradient.colors = [UIColor.red.cgColor, UIColor.black.cgColor]
            
            gradient.locations = [0.0, 0.2, 0.7, 1.0]
            gradient.colors = [UIColor.clear.cgColor, UIColor.clear.cgColor, UIColor.black.cgColor, UIColor.black.cgColor]
        }
    }
    
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
}

class OnboardingViewControllerTemplate: UIViewController {

    @IBOutlet weak var stackView: UIStackView!
    @IBOutlet weak var demoImageView: UIImageView!
    
    override func viewDidLoad() {
        super.viewDidLoad()
    }
    

    override func viewDidLayoutSubviews() {
        super.viewDidLayoutSubviews()
        
        print(">>>> self.demoImageView.bounds.width \(self.demoImageView.bounds.width)")
        print(">>>> self.stackView.bounds.width \(self.stackView.bounds.width)")
        
        demoImageView.subviews.forEach({ $0.removeFromSuperview() })

        let v = GradientView()
        v.frame = CGRect(
            x: 0,
            y: self.demoImageView.bounds.height - 300,
            width: self.stackView.bounds.width, // ?? bug
            height: 300
        )
        
        self.demoImageView.addSubview(v)
    }
}