RoundShadowView.swift

/* 
  Example of how to create a view that has rounded corners and a shadow.
  These cannot be on the same layer because setting the corner radius requires masksToBounds = true.
  When it's true, the shadow is clipped.
  It's possible to add sublayers and set their path with a UIBezierPath(roundedRect...), but this becomes difficult when using AutoLayout.
  Instead, we a containerView for the cornerRadius and the current view for the shadow.
  All subviews should just be added and constrained to the containerView
*/

import UIKit

class RoundShadowView: UIView {
  
    let containerView = UIView()
    let cornerRadius: CGFloat = 6.0
  
    override init(frame: CGRect) {
        super.init(frame: frame)

        layoutView()
    }

    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

    func layoutView() {
      
      // set the shadow of the view's layer
      layer.backgroundColor = UIColor.clear.cgColor
      layer.shadowColor = UIColor.black.cgColor
      layer.shadowOffset = CGSize(width: 0, height: 1.0)
      layer.shadowOpacity = 0.2
      layer.shadowRadius = 4.0
        
      // set the cornerRadius of the containerView's layer
      containerView.layer.cornerRadius = cornerRadius
      containerView.layer.masksToBounds = true
      
      addSubview(containerView)
      
      //
      // add additional views to the containerView here
      //
      
      // add constraints
      containerView.translatesAutoresizingMaskIntoConstraints = false
      
      // pin the containerView to the edges to the view
      containerView.leadingAnchor.constraint(equalTo: leadingAnchor).isActive = true
      containerView.trailingAnchor.constraint(equalTo: trailingAnchor).isActive = true
      containerView.topAnchor.constraint(equalTo: topAnchor).isActive = true
      containerView.bottomAnchor.constraint(equalTo: bottomAnchor).isActive = true
    }
}