Custom UIView hosting a CAShapeLayer

CircleView.swift

// known-good: Xcode 8.2.1, Swift 3, 2017-02-08

/**
 Draws a circle, centered in the view, with the specified radius
 */
class CircleView: UIView
{
  // API
  var circleRadius:CGFloat = 15 {
    didSet { self.setNeedsLayout() }
  }
  var color:UIColor = .black {
    didSet { self.shapeLayer.fillColor = color.cgColor  }
  }
  
  override static var layerClass:AnyClass {
    return CAShapeLayer.self
  }
  
  private var shapeLayer:CAShapeLayer {
    return self.layer as! CAShapeLayer
  }
  
  override func layoutSubviews() {
    super.layoutSubviews()
    self.shapeLayer.path = self.circlePath()
  }

  private func circlePath() -> CGPath {
    let center = CGPoint(x: self.layer.bounds.midX, y: self.layer.bounds.midY)
    let circleRect = CGRect(origin: center, size: .zero).insetBy(dx: -1*circleRadius, dy: -1*circleRadius)
    let satelittePath = UIBezierPath(ovalIn: circleRect).cgPath
    return satelittePath
  }
}