CheckBoxSingleselectButton.swift

import UIKit

final class CheckBoxSingleselectButton: UIExpandedTouchAreaButton {
    private var shapeLayerRect: CGRect {
        let width = bounds.width / 1.4
        let height = bounds.height / 1.4
        return CGRect(x: (bounds.width - width) / 2,
                          y: (bounds.height - height) / 2,
                          width: width,
                          height: height)
    }
    
    private var blueShapeLayer: CAShapeLayer {
        let layer = CAShapeLayer()
        layer.path = UIBezierPath(roundedRect: shapeLayerRect, cornerRadius: 3).cgPath
        layer.fillColor = UIColor.lightRoyalBlue.cgColor
        return layer
    }
    
    private var whiteShapeLayer: CAShapeLayer {
        let layer = CAShapeLayer()
        layer.path = UIBezierPath(roundedRect: shapeLayerRect, cornerRadius: 3).cgPath
        layer.fillColor = UIColor.white.cgColor
        return layer
    }
    
    override func awakeFromNib() {
        super.awakeFromNib()
        
        backgroundColor = .white
        layer.cornerRadius = 5
        tintColor = .clear
    }
    
    override var isSelected: Bool {
        didSet {
            if isSelected {
                layer.borderWidth = 1
                layer.borderColor = UIColor.blue.cgColor
                backgroundColor = .white
                layer.addSublayer(blueShapeLayer)
            } else {
                layer.borderWidth = 1
                layer.borderColor = UIColor.grey.cgColor
                backgroundColor = .white
                layer.addSublayer(whiteShapeLayer)
            }
        }
    }
}