Custom TabBarViewController

TabBarViewController.swift

import UIKit

extension UIColor {
    convenience init(hex: UInt32, alpha: CGFloat = 1) {
        let r = CGFloat((hex & 0xFF0000) >> 16) / 255
        let g = CGFloat((hex & 0x00FF00) >> 8) / 255
        let b = CGFloat(hex & 0x0000FF) / 255
        self.init(red: r, green: g, blue: b, alpha: alpha)
    }
}

final class DummyViewController: UIViewController {
    private var text: String
    private var color: UIColor

    init(text: String, color: UIColor) {
        self.text = text
        self.color = color
        super.init(nibName: nil, bundle: nil)
    }

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

    override func loadView() {
        let label = UILabel()
        label.text = text
        label.backgroundColor = color
        label.font = .boldSystemFont(ofSize: 40)
        label.textColor = .white
        label.textAlignment = .center
        view = label
    }

    override func viewDidLoad() {
        super.viewDidLoad()
        print(#function, text)
    }

    override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)
        print(#function, text)
    }

    override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)
        print(#function, text)
    }

    override func viewWillDisappear(_ animated: Bool) {
        super.viewWillAppear(animated)
        print(#function, text)
    }

    override func viewDidDisappear(_ animated: Bool) {
        super.viewDidDisappear(animated)
        print(#function, text)
    }
}


protocol TabViewDelegate: AnyObject {
    func didSelectTab(_ selectedIndex: Int)
}

final class TabView: UIView {
    weak var delegate: TabViewDelegate?

    private var buttons: [UIButton] = []

    override init(frame: CGRect) {
        super.init(frame: frame)
        initializeView()
    }

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

    override func layoutSubviews() {
        super.layoutSubviews()
        let width = bounds.width / CGFloat(buttons.count)
        let height = bounds.height
        buttons.enumerated().forEach { index, button in
            button.frame = CGRect(
                origin: CGPoint(x: width * CGFloat(index), y: 0),
                size: CGSize(width: width, height: height)
            )
        }
    }
}

private extension TabView {
    func initializeView() {
        buttons = (0...3).map { index in
            let button = UIButton()
            button.tag = index
            button.setTitle(index.description, for: .normal)
            button.titleLabel?.font = .boldSystemFont(ofSize: 28)
            button.setTitleColor(.white, for: .normal)
            button.backgroundColor = .black
            button.addTarget(self, action: #selector(selectButton), for: .touchUpInside)
            addSubview(button )
            return button
        }
    }

    @objc func selectButton(_ sender: UIButton) {
        delegate?.didSelectTab(sender.tag)
    }
}

final class TabViewController: UIViewController {
    private let contentView = UIView()
    private let tabView = TabView()
    private let viewControllers = [
        DummyViewController(text: "0", color: UIColor(hex: 0xffc4e4)),
        DummyViewController(text: "1", color: UIColor(hex: 0xc4f4ff)),
        DummyViewController(text: "2", color: UIColor(hex: 0xcfffd9)),
        DummyViewController(text: "3", color: UIColor(hex: 0xddd1ff))
    ]

    private var selectedViewController: UIViewController?

    override func viewDidLoad() {
        super.viewDidLoad()
        view.addSubview(contentView)
        tabView.delegate = self
        view.addSubview(tabView)

        if let firstViewController = viewControllers.first {
            selectedViewController = firstViewController
            add(controller: firstViewController)
        }
    }

    override func viewDidLayoutSubviews() {
        super.viewDidLayoutSubviews()
        let tabviewHeight: CGFloat = 80
        contentView.frame = CGRect(
            origin: .zero,
            size: CGSize(width: view.bounds.width, height: view.bounds.height - tabviewHeight)
        )
        tabView.frame = CGRect(
            origin: CGPoint(x: 0, y: contentView.bounds.height),
            size: CGSize(width: view.bounds.width, height: tabviewHeight)
        )
    }
}

extension TabViewController: TabViewDelegate {
    func didSelectTab(_ selectedIndex: Int) {
        guard let fromViewController = selectedViewController,
            viewControllers.count > selectedIndex else {
                return
        }

        let toViewController = viewControllers[selectedIndex]
        if fromViewController !== toViewController {
            toViewController.beginAppearanceTransition(true, animated: true)
            fromViewController.beginAppearanceTransition(false, animated: true)

            add(controller: toViewController)
            remove(controller: fromViewController)

            fromViewController.endAppearanceTransition()
            toViewController.endAppearanceTransition()

            selectedViewController = toViewController
        }
    }
}

private extension TabViewController {
    func add(controller: UIViewController) {
        controller.willMove(toParent: self)
        addChild(controller)
        controller.view.frame = view.bounds
        contentView.addSubview(controller.view)
    }

    func remove(controller: UIViewController) {
        controller.willMove(toParent: nil)
        controller.removeFromParent()
        controller.view.removeFromSuperview()
    }
}