IOS | Unable to change root view controller in app delegate

Question

I am building an app whose root view controller must be changed if the user is logged in. Say if the user is logged in I must show a tab bar controller as the home screen if

Answer 1

If you are targeting only iOS 13+, the only change you should need to make is to add one line:

    window?.rootViewController = initialViewController

    // add this line
    self.window = window

    window?.makeKeyAndVisible()

If you want to support earlier iOS versions, here is a complete SceneDelegate / AppDelegate implementation:

SceneDelegate.swift

//
//  SceneDelegate.swift
//  Created by Don Mag on 3/27/20.
//

import UIKit

// entire class is iOS 13+
@available(iOS 13.0, *)
class SceneDelegate: UIResponder, UIWindowSceneDelegate {

    var window: UIWindow?

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

        print("Scene Delegate willConnectTo", UserDefaults.standard.bool(forKey: "isLoggedIn"))

        guard let windowScene = (scene as? UIWindowScene) else { return }
        let window = UIWindow(frame: windowScene.coordinateSpace.bounds)
        window.windowScene = windowScene

        if UserDefaults.standard.bool(forKey: "isLoggedIn") {
            guard let vc = UIStoryboard(name: "Main", bundle: nil).instantiateViewController(withIdentifier: "HomeVC") as? TabController else {
                fatalError("Could not instantiate HomeVC!")
            }
            window.rootViewController = vc
        } else {
            guard let vc = UIStoryboard(name: "Main", bundle: nil).instantiateViewController(withIdentifier: "AuthVC") as? AuthViewController else {
                fatalError("Could not instantiate HomeVC!")
            }
            window.rootViewController = vc
        }

        self.window = window

        window.makeKeyAndVisible()
    }

}

AppDelegate.swift

//
//  AppDelegate.swift
//  Created by Don Mag on 3/27/20.
//

import UIKit

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {

    var window : UIWindow?
    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey : Any]?) -> Bool {
            if #available(iOS 13, *) {
                // do only pure app launch stuff, not interface stuff
            } else {

                print("App Delegate didFinishLaunching... isLoggedIn:", UserDefaults.standard.bool(forKey: "isLoggedIn"))

                self.window = UIWindow()

                if UserDefaults.standard.bool(forKey: "isLoggedIn") {
                    guard let vc = UIStoryboard(name: "Main", bundle: nil).instantiateViewController(withIdentifier: "HomeVC") as? TabController else {
                        fatalError("Could not instantiate HomeVC!")
                    }
                    window?.rootViewController = vc
                } else {
                    guard let vc = UIStoryboard(name: "Main", bundle: nil).instantiateViewController(withIdentifier: "AuthVC") as? AuthViewController else {
                        fatalError("Could not instantiate HomeVC!")
                    }
                    window?.rootViewController = vc
                }

                window?.makeKeyAndVisible()

            }
            return true
    }

    // MARK: UISceneSession Lifecycle

    // iOS 13+ only
    @available(iOS 13.0, *)
    func application(_ application: UIApplication, configurationForConnecting connectingSceneSession: UISceneSession, options: UIScene.ConnectionOptions) -> UISceneConfiguration {
        return UISceneConfiguration(name: "Default Configuration", sessionRole: connectingSceneSession.role)
    }
    // iOS 13+ only
    @available(iOS 13.0, *)
    func application(_ application: UIApplication, didDiscardSceneSessions sceneSessions: Set<UISceneSession>) {
    }

}

Answer 2

Here's a way to extend your UIWindow (and access to your rootViewController) into your view controllers to make it easier to change your rootviewcontroller throughout your app:

extension UIViewController {
    var appDelegate: AppDelegate {
    return UIApplication.shared.delegate as! AppDelegate
}

var sceneDelegate: SceneDelegate? {
    guard let windowScene = UIApplication.shared.connectedScenes.first as? UIWindowScene,
        let delegate = windowScene.delegate as? SceneDelegate else { return nil }
     return delegate
}}
   





extension UIViewController {   
        var window: UIWindow? {
            if #available(iOS 13, *) {
                guard let windowScene = UIApplication.shared.connectedScenes.first as? UIWindowScene,
                    let delegate = windowScene.delegate as? SceneDelegate, let window = delegate.window else { return nil }
                       return window
            }
            
            guard let delegate = UIApplication.shared.delegate as? AppDelegate, let window = delegate.window else { return nil }
            return window
        }
    }