A view that combines shadow, corner radius, and translucent background into one view

ShadowCutoutView.swift

class ShadowCutoutView: UIView {
    var contentView: UIView? {
        didSet {
            oldValue?.removeFromSuperview()

            guard let contentView else {
                return
            }

            contentView.autoresizingMask = [.flexibleWidth, .flexibleHeight]
            addSubview(contentView)
        }
    }

    let shadowLayer = CALayer()

    private let shadowMaskLayer = CAShapeLayer()

    override init(frame: CGRect) {
        super.init(frame: frame)

        shadowLayer.mask = shadowMaskLayer
        layer.addSublayer(shadowLayer)
    }
    
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

    override func layoutSubviews() {
        super.layoutSubviews()

        let shadowCornerRadius = contentView?.layer.cornerRadius ?? 0
        let shadowPadding = shadowLayer.shadowRadius * 4

        shadowLayer.frame = bounds
        shadowLayer.shadowPath = UIBezierPath(roundedRect: bounds, cornerRadius: shadowCornerRadius).cgPath

        let maskFrame = CGRect(
            x: -shadowPadding,
            y: -shadowPadding,
            width: bounds.width + shadowPadding * 2,
            height: bounds.height + shadowPadding * 2
        )
        let maskPath = UIBezierPath(rect: CGRect(origin: .zero, size: maskFrame.size))
        let cutoutPath = UIBezierPath(
            roundedRect: bounds.offsetBy(dx: shadowPadding, dy: shadowPadding),
            cornerRadius: shadowCornerRadius
        )
        maskPath.append(cutoutPath.reversing())

        shadowMaskLayer.frame = maskFrame
        shadowMaskLayer.path = maskPath.cgPath
    }
}

// Shadow parameters are adjusted through `shadowLayer` property instead
let view = ShadowCutoutView()
view.shadowLayer.shadowOffset = .zero
view.shadowLayer.shadowColor = UIColor.black.cgColor
view.shadowLayer.shadowRadius = 20
view.shadowLayer.shadowOpacity = 1

// Shadow corner radius is determined by corner radius of the content view
let contentView = UIView()
contentView.clipsToBounds = true
contentView.layer.cornerRadius = 20
view.contentView = contentView