NotificationCenterRetainCycle.swift

import UIKit

class ListViewController: UIViewController {
   let label = UILabel(frame: CGRect(x: 100, y: 200, width: 300, height: 50))

    override func viewDidLoad() {
        super.viewDidLoad()
        view.backgroundColor = .white

        label.text = "Animating"
        view.addSubview(label)
        let controller = DetailViewController()
        controller.definesPresentationContext = true
        let navControll = UINavigationController(rootViewController: controller)
        self.navigationController?.present(navControll, animated: true, completion: nil)

        NotificationCenter.default.addObserver(forName: .titleUpdated, object: nil, queue: nil) {_ in
            UIView.animate(withDuration: 0.3, animations: {
                self.label.textColor = .green
            })
        }
    }

    deinit {
        print("Deinit")
    }
}

class DetailViewController: UIViewController {
    var listTitle: (() -> String)?
    
    override func viewDidLoad() {
        super.viewDidLoad()
        NotificationCenter.default.post(name: .titleUpdated, object: nil)
    }
}

extension Notification.Name {
    static let titleUpdated = Notification.Name("titleUpdated")
}