Swift: Custom UIButton subclass that displays a rounded rectangle in the background

RoundRectButton.swift

import UIKit

/// UIButton subclass that draws a rounded rectangle in its background.

public class RoundRectButton: UIButton {

    // MARK: Public interface

    /// Corner radius of the background rectangle
    public var roundRectCornerRadius: CGFloat = 8 {
        didSet {
            self.setNeedsLayout()
        }
    }

    /// Color of the background rectangle
    public var roundRectColor: UIColor = UIColor.whiteColor() {
        didSet {
            self.setNeedsLayout()
        }
    }

    // MARK: Overrides

    override public func layoutSubviews() {
        super.layoutSubviews()
        layoutRoundRectLayer()
    }

    // MARK: Private

    private var roundRectLayer: CAShapeLayer?

    private func layoutRoundRectLayer() {
        if let existingLayer = roundRectLayer {
            existingLayer.removeFromSuperlayer()
        }
        let shapeLayer = CAShapeLayer()
        shapeLayer.path = UIBezierPath(roundedRect: self.bounds, cornerRadius: roundRectCornerRadius).CGPath
        shapeLayer.fillColor = roundRectColor.CGColor
        self.layer.insertSublayer(shapeLayer, atIndex: 0)
        self.roundRectLayer = shapeLayer
    }
}