NavigationControllerCompletion-2016.swift

import UIKit

extension UINavigationController {
    
    func pushViewController(_ viewController: UIViewController, animated: Bool = true, completion: @escaping(Void) -> Void) {
        pushViewController(viewController, animated: animated)
        
        guard animated, let coordinator = transitionCoordinator else {
            completion()
            return
        }
        
        coordinator.animate(alongsideTransition: nil, completion: { _ in
            completion()
        })
    }
    
}