ReusableViewController(UsingObjcOptionalMethodsSingleDelegate).swift

import UIKit

@objc protocol ReusableViewControllerDelegate {
    @objc optional func viewDidLoad()
    @objc optional func viewWillAppear(_ animated: Bool)
}

final class ReusableViewController: UIViewController {
    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?.viewDidLoad?()
    }

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