UINavigationController app以编程方式委托UIViewController

Question

I'm trying to create a UINavigationController and two UIVewControllers programmatically and be able to transition from the first VC to the second VC and back using the navigation controller. I've tried different methods for getting this to work. I've left some lines in the source code commented out to give hints of things that I've tried.

With the current method I'm getting this warning (it doesn't work):

Warning: Attempt to present <x.VC2: 0x7fd27240df00> on <x.VC1: 0x7fd27240db60> whose view is not in the window hierarchy!

In AppDelegate.swift:

func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
    let navcon = UINavigationController()
    //navcon.viewControllers = [VC1(), VC2()]    // tried this without success
    navcon.viewControllers = [VC1()]

    window = UIWindow()
    window?.makeKeyAndVisible()
    //window?.rootViewController = VC1()         // one variation that I tried

    window?.rootViewController = navcon.viewControllers[0]
    return true
}

In VC1.swift:

var navcon: UINavigationController!
let vc2 = VC2()

//---------------------------------------------

override func viewDidLoad() {
    super.viewDidLoad()
    navcon = self.navigationController
    //navcon?.viewControllers.append(vc2)
    let x = navcon?.viewControllers
    let n = x?.count
}

//---------------------------------------------

func triggeredFunction()  {
    self.present(vc2, animated: true, completion: nil)
    //navcon.pushViewController(vc2, animated: true)
}

Answer 1

Result:

Code:

AppDelegate:

    window = UIWindow()
    let firstVC = FirstViewController()
    let navigationController = UINavigationController(rootViewController: firstVC)
    window?.rootViewController = navigationController
    window?.makeKeyAndVisible()

FirstVC:

override func viewDidLoad() {
    super.viewDidLoad()

    view.backgroundColor = .green

    let button = UIButton(frame: CGRect(x: 100, y: 100, width: 100, height: 100))
    button.backgroundColor = .red
    view.addSubview(button)
    button.addTarget(self, action: #selector(showSecondVC), for: .touchUpInside)
}

@objc func showSecondVC() {
    let secondVC = SecondViewController()
    navigationController?.pushViewController(secondVC, animated: true)
}

SecondVC:

view.backgroundColor = .yellow

Hope it helps! Please let me know if it works for you or not.