ShadowView.swift

import UIKit

class ShadowView: UIView {

    var color: UIColor? {
        didSet {
            self.setNeedsDisplay()
        }
    }
    
    var cornerRadius: CGFloat = 16 {
        didSet {
            self.setNeedsDisplay()
        }
    }
    
    var shadowOpacity: Float = 0.4 {
        didSet {
            self.setNeedsDisplay()
        }
    }
    
    var shadowRadius: CGFloat = 16 {
        didSet {
            self.setNeedsDisplay()
        }
    }
    
    var shadowColor: UIColor = .black {
        didSet {
            self.setNeedsDisplay()
        }
    }
    
    private lazy var backgroundLayer: CAShapeLayer = {
        let backgroundLayer = CAShapeLayer()
        backgroundLayer.cornerRadius = cornerRadius
        backgroundLayer.masksToBounds = true
        return backgroundLayer
    }()
    
    private lazy var shadowLayer: CAShapeLayer = {
        let shadowLayer = CAShapeLayer()
        shadowLayer.fillColor = UIColor.clear.cgColor
        return shadowLayer
    }()
    
    override func draw(_ rect: CGRect) {
        super.draw(rect)
        self.backgroundColor = UIColor.clear
        
        backgroundLayer.frame = rect
        backgroundLayer.backgroundColor = color?.cgColor
        
        shadowLayer.frame = rect
        shadowLayer.shadowPath = UIBezierPath(roundedRect: rect, cornerRadius: cornerRadius).cgPath
        shadowLayer.shadowColor = shadowColor.cgColor
        shadowLayer.shadowOffset = CGSize(width: 0, height: 0)
        shadowLayer.shadowOpacity = shadowOpacity
        shadowLayer.shadowRadius = shadowRadius
        
        self.layer.insertSublayer(shadowLayer, at: 0)
        self.layer.insertSublayer(backgroundLayer, above: shadowLayer)
    }
    
    override func layoutSubviews() {
        super.layoutSubviews()
        self.backgroundLayer.frame = self.bounds
        self.shadowLayer.frame = self.bounds
        shadowLayer.shadowPath = UIBezierPath(roundedRect: self.bounds, cornerRadius: cornerRadius).cgPath
    }

}