Creating a navigationController programmatically (Swift)

Value of type 'AppDelegate' has no member 'window'

For those building newer projects with SceneDelegate.swift, you can use the 'var window: UIWindow?' in SceneDelegate instead of the removed 'var window' in AppDelegate

func scene(_ scene: UIScene, willConnectTo session: UISceneSession, options connectionOptions: UIScene.ConnectionOptions) {
    guard let windowScene = (scene as? UIWindowScene) else { return }

    window?.windowScene = windowScene
    window?.makeKeyAndVisible()

    let viewController = ViewController()
    let navViewController = UINavigationController(rootViewController: viewController)
    window?.rootViewController = navViewController
}

I would recommend starting your AppDelegate with this skeleton:

1) use let wherever you can!

2) UINavigationController has the rootViewController property.

func application(application: UIApplication, didFinishLaunchingWithOptions launchOptions: [NSObject: AnyObject]?) -> Bool {
    let viewController = ViewController(nibName: nil, bundle: nil) //ViewController = Name of your controller
    let navigationController = UINavigationController(rootViewController: viewController)

    self.window = UIWindow(frame: UIScreen.mainScreen().bounds)
    self.window?.rootViewController = navigationController
    self.window?.makeKeyAndVisible()

    return true
}

Swift 1, 2:

func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
   self.window = UIWindow(frame: UIScreen.mainScreen().bounds)
   var nav1 = UINavigationController()
   var mainView = ViewController(nibName: nil, bundle: nil) //ViewController = Name of your controller
   nav1.viewControllers = [mainView]
   self.window!.rootViewController = nav1
   self.window?.makeKeyAndVisible()
}

Swift 4+: and Swift 5+

func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
   self.window = UIWindow(frame: UIScreen.main.bounds)
   let nav1 = UINavigationController()
   let mainView = ViewController(nibName: nil, bundle: nil) //ViewController = Name of your controller
   nav1.viewControllers = [mainView]
   self.window!.rootViewController = nav1
   self.window?.makeKeyAndVisible()
}

Here is another take in the SceneDelegate class:

var window: UIWindow?

func scene(_ scene: UIScene, willConnectTo session: UISceneSession, options connectionOptions: UIScene.ConnectionOptions) {

    if let windowScene = scene as? UIWindowScene {

        let window = UIWindow(windowScene: windowScene)    
        let navController = UINavigationController()
        let viewController = ViewController()

        navController.viewControllers = [viewController]            
        window.rootViewController = navController
        self.window = window
        window.makeKeyAndVisible()
    }
}