Vertical button with underline view

VerticleButton+UnderlineView.swift

//
//  ViewController.swift
//  Button
//
//  Created by Glenn Posadas on 6/23/22.
//

import UIKit

class ViewController: UIViewController {
    
    
    var button: VerticalButton!
    
    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view.
        
        view.backgroundColor = .red
        
        button = VerticalButton(icon: .init(named: "ic_poll_results")!, title: "Results")
        button.addTarget(self, action: #selector(boom), for: .touchUpInside)
        button.translatesAutoresizingMaskIntoConstraints = false
        
        view.addSubview(button)
        
        NSLayoutConstraint.activate([
            button.centerYAnchor.constraint(equalTo: view.centerYAnchor),
            button.centerXAnchor.constraint(equalTo: view.centerXAnchor),
            button.widthAnchor.constraint(equalToConstant: 50),
            button.heightAnchor.constraint(equalToConstant: 50),
        ])
        
    }
    
    @objc
    func boom() {
        button.isSelected.toggle()
    }
    
}

/**
 A custom `UIButton` that has custom label and imageView
 which are both aligned vertically. Image at the top, label at the bottom.
 */
class VerticalButton: UIButton {
    
    private(set) var icon: UIImage!
    private(set) var title: String!
    private(set) var underlineView: UIView!
    private var contentView: UIView!
    
    convenience init(icon: UIImage, title: String) {
        self.init(frame: .zero)
        
        self.icon = icon
        self.title = title
        
        layout()
    }
    
    override var isSelected: Bool {
        didSet {
            UIView.animate(withDuration: 0.1) {
                self.underlineView.alpha = self.isSelected ? 1 : 0
            }
        }
    }
    
    override var isHighlighted: Bool {
        didSet {
            self.contentView.alpha = self.isHighlighted ? 0.6 : 1.0
        }
    }
}

private extension VerticalButton {
    
    func layout() {
        let imageView = UIImageView(image: icon)
        imageView.isUserInteractionEnabled = false
        imageView.contentMode = .scaleAspectFit
        
        let titleLabel = UILabel()
        titleLabel.font = .systemFont(ofSize: 14)
        titleLabel.text = title
        titleLabel.textAlignment = .center
        titleLabel.isUserInteractionEnabled = false
        titleLabel.textColor = .white
        
        let stackView = UIStackView(arrangedSubviews: [
            imageView,
            titleLabel
        ])
        stackView.axis = .vertical
        stackView.spacing = 4
        stackView.isUserInteractionEnabled = false
        stackView.translatesAutoresizingMaskIntoConstraints = false
        
        underlineView = UIView()
        underlineView.alpha = isSelected ? 1 : 0
        underlineView.backgroundColor = .white
        underlineView.isUserInteractionEnabled = false
        underlineView.translatesAutoresizingMaskIntoConstraints = false
        
        contentView = UIView()
        contentView.isUserInteractionEnabled = false
        contentView.translatesAutoresizingMaskIntoConstraints = false
        
        addSubview(contentView)
        contentView.addSubview(stackView)
        contentView.addSubview(underlineView)
        
        NSLayoutConstraint.activate([
            contentView.topAnchor.constraint(equalTo: topAnchor),
            contentView.bottomAnchor.constraint(equalTo: bottomAnchor),
            contentView.leadingAnchor.constraint(equalTo: leadingAnchor),
            contentView.trailingAnchor.constraint(equalTo: trailingAnchor),
            
            stackView.topAnchor.constraint(equalTo: contentView.topAnchor),
            stackView.bottomAnchor.constraint(equalTo: contentView.bottomAnchor),
            stackView.leadingAnchor.constraint(equalTo: contentView.leadingAnchor),
            stackView.trailingAnchor.constraint(equalTo: contentView.trailingAnchor),
            
            underlineView.leadingAnchor.constraint(equalTo: titleLabel.leadingAnchor),
            underlineView.trailingAnchor.constraint(equalTo: titleLabel.trailingAnchor),
            underlineView.heightAnchor.constraint(equalToConstant: 1),
            underlineView.topAnchor.constraint(equalTo: titleLabel.bottomAnchor)
        ])
    }
}