Circular UIView with drop shadow (using UIBezierPath)

1_playground.swift

import UIKit
import PlaygroundSupport

let container = UIView(frame: CGRect(x: 0, y: 0, width: 500, height: 200))
container.backgroundColor = .lightGray

let buttonRadius: CGFloat = 50
let buttonSize = CGSize(width: buttonRadius * 2, height: buttonRadius * 2)
let buttonPath = UIBezierPath(arcCenter: CGPoint(x: buttonRadius, y: buttonRadius), radius: buttonRadius, startAngle: 0, endAngle: CGFloat.pi * 2, clockwise: true)

// only for shadow
let buttonBackgroundView = UIView(frame: CGRect(origin: .zero, size: buttonSize))
buttonBackgroundView.backgroundColor = .clear
buttonBackgroundView.center = container.center
buttonBackgroundView.layer.masksToBounds = false
buttonBackgroundView.layer.cornerRadius = buttonRadius
buttonBackgroundView.layer.shadowOffset = .zero
buttonBackgroundView.layer.shadowRadius = 5
buttonBackgroundView.layer.shadowOpacity = 0.5
buttonBackgroundView.layer.shadowPath = buttonPath.cgPath
container.addSubview(buttonBackgroundView)

// circle button view
let buttonView = UIView(frame: CGRect(origin: .zero, size: buttonSize))
buttonView.backgroundColor = .white
buttonView.frame.origin = .zero
let buttonShape = CAShapeLayer()
buttonShape.path = buttonPath.cgPath
buttonView.layer.mask = buttonShape
buttonBackgroundView.addSubview(buttonView)

PlaygroundPage.current.liveView = container

2_fig.png