Swift 3 trying to create and use a UINavigationController programmatically - swift3

Question

I'm working on an existing application which uses the storyboard but I want to continue development without using the storyboard at all, or nib files.
The existing left menu is a UITableView which is not the root controller and does not have a navigation controller associated with it. I have created a UINavigationController in the app delegate and want to use this navigation controller to push a new controller. I am able to present a view controller but I want to use push in order to conform with the current UIX.
In the following code nothing happens because navigationController? returns nil.
Here is my new code in the app delegate.
#UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {
var window: UIWindow?
var navController: UINavigationController?
func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
navController = UINavigationController()
self.window = UIWindow(frame: UIScreen.main.bounds)
self.window!.rootViewController = navController
self.window!.backgroundColor = .red
self.window!.makeKeyAndVisible()
let menuViewController = SideMenuViewController()
menuViewController.navController = navController
Then in my side menu controller:
import UIKit
class SideMenuViewController: UIViewController {
var navController: UINavigationController?
.......
let myViewController = myViewController()
self.navigationController?.pushViewController(myViewController, animated: true )

Answer 1

From the UIViewController documentation:
var navigation​Controller:​ UINavigation​Controller?
The nearest
ancestor in the view controller hierarchy that is a navigation
controller.
Which means when you call self.navigationController in a view controller you get the (nearest) navigation controller that self is embedded in. Apparently your menu controller is not embedded in the navigation controller hierarchy. Using your app delegate's navController member is one way to make this work. Then you can say in your menu view controller:
func menuItemFooSelected()
{
let navController = (UIApplication.shared.delegate as! AppDelegate).navController
let myViewController = myViewController()
navController?.pushViewController(myViewController, animated: true)
}
Alternatively (and probably preferably), when you set up your initial structure in your app delegate, inject the navigation controller into the side menu controller:
class MenuViewController: UIViewController
{
var navController: UINavigationController?
...
func menuItemFooSelected()
{
let myViewController = myViewController()
self.navController?.pushViewController(myViewController, animated: true)
}
}
In application(_:didFinishLaunchingWithOptions:)
...
let menuViewController = MenuViewController(...)
menuViewController.navController = navController