ReusableViewController(UsingEnum).swift

import UIKit

protocol ReusableViewControllerDelegate {
    func handle(_ event: ReusableViewController.Event)
}

final class ReusableViewController: UIViewController {
    enum Event {
        case viewDidLoad
        case viewWillAppear(_ animated: Bool)
    }

    var delegate: ReusableViewControllerDelegate?
    private let contentView: UIView

    init(with view: UIView) {
        self.contentView = view
        super.init(nibName: nil, bundle: nil)
    }

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

    override func loadView() {
        super.loadView()
        self.view = contentView
    }

    override func viewDidLoad() {
        super.viewDidLoad()
        delegate?.handle(.viewDidLoad)
    }

    override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)
        delegate?.handle(.viewWillAppear(animated))
    }
}