NavigationBarController.swift

import UIKit

class FeedViewController: UIViewController {
    lazy var navigationBarController: NavigationBarController = {
        NavigationBarController()
    }()
    override var navigationItem: UINavigationItem {
        return navigationBarController.navigationItem
    }
    override func viewDidLoad() {
        super.viewDidLoad()
        view.backgroundColor = .white
        add(child: navigationBarController)
    }
}

extension FeedViewController {
    class NavigationBarController: UIViewController {
        override func viewDidLoad() {
            super.viewDidLoad()
            view.backgroundColor = .clear
            title = "Feed"
            navigationItem.searchController = UISearchController(searchResultsController: nil)
            navigationItem.rightBarButtonItem = UIBarButtonItem(barButtonSystemItem: .add, target: nil, action: nil)
            navigationItem.leftBarButtonItem = UIBarButtonItem(barButtonSystemItem: .camera, target: nil, action: nil)
        }
    }
}

extension UIViewController {
    func add(child: UIViewController) {
        addChild(child)
        child.didMove(toParent: self)
        view.addSubview(child.view)
    }
}