Dismiss and Present View Controller in Swift

You have to get the viewController which presented self (current ViewController). If that view controller is rootViewController, then you can use the code below, if not then query it based on your view controller hierarchy.

if let vc3 = self.storyboard?.instantiateViewController(withIdentifier: "vc3") as? ViewController3 {
    let appDelegate = UIApplication.shared.delegate as! AppDelegate
    appDelegate.window?.rootViewController!.present(vc3, animated: true, completion: nil)
}

you can't do that because when the UIViewController A calls the UIViewController B and the first controller is dismissed then the two controllers are nil.

You need to have a UIViewController as a base, in this case MainViewController is the base. You need to use a protocol to call the navigation between controllers.

you can do using protocol let say for example as bellow:-

In to your viewController setting Protocol :

    protocol FirstViewControllerProtocol {
    func dismissViewController()
}

class FirstViewController: UIViewController {
    var delegate:FirstViewControllerProtocol!

    override func viewDidLoad() {
        super.viewDidLoad()

        // Do any additional setup after loading the view.
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }


    @IBAction func goBack(sender: AnyObject) {
        self.dismissViewControllerAnimated(true) { 
            self.delegate!.dismissViewController()
        }
    }

Now in your main view controller

class MainViewController: UIViewController, FirstViewControllerProtocol {

override func viewDidLoad() {
    super.viewDidLoad()
    // Do any additional setup after loading the view, typically from a nib.
}

override func didReceiveMemoryWarning() {
    super.didReceiveMemoryWarning()
    // Dispose of any resources that can be recreated.
}


@IBAction func goToFirstViewController(sender: AnyObject) {
    let viewController = self.storyboard?.instantiateViewControllerWithIdentifier(String(FirstViewController)) as! FirstViewController
    viewController.delegate = self
    self.presentViewController(viewController, animated: true, completion: nil)
}



//MARK: Protocol
func dismissViewController() {
    if let viewController = self.storyboard?.instantiateViewControllerWithIdentifier(String(SecondViewController)){
        self.presentViewController(viewController, animated: true, completion: nil)
    }
}

Code example with storyboard:

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