ios - AlertController is not in the window hierarchy

Question

I've just created a Single View Application project with ViewController class. I would like to show a UIAlertController from a function which is located inside my own class.

Here is my class with an alert.

class AlertController: UIViewController {
     func showAlert() { 
         var alert = UIAlertController(title: "abc", message: "def", preferredStyle: .Alert)
         self.presentViewController(alert, animated: true, completion: nil)
     }
}

Here is ViewController which executes the alert.

class ViewController: UIViewController {
   override func viewDidLoad() {
       super.viewDidLoad()  
   }

   @IBAction func showAlertButton(sender: AnyObject) {
       var alert = AlertController()
       alert.showAlert()
   }
}

This is what I get instead of a beautiful alert.

Warning: Attempt to present UIAlertController: 0x797d2d20 on Sprint1.AlertController: 0x797cc500 whose view is not in the window hierarchy!

What should I do?

Answer 1

If you're instancing your UIAlertController from a modal controller, you need to do it in viewDidAppear, not in viewDidLoad or you'll get an error.

Here's my code (Swift 4):

override func viewDidAppear(_ animated: Bool) {
    super.viewDidAppear(animated)

    let alertController = UIAlertController(title: "Foo", message: "Bar", preferredStyle: .alert)

    alertController.addAction(UIAlertAction(title: "OK", style: .cancel, handler: nil))
    present(alertController, animated: true, completion: nil)
}