Prevent UIAlertController to dismiss

EDIT: Updated for Swift 5

EDIT: Updated to include @skywalker’s feedback

So I actually got this to work. In short, it involves adding a long-press gesture recognizer to the UIAlertController that triggers before the dismissal occurs.

First, create lazily loaded computed variables in your view controller for your UIAlertController and the UIAlertAction you want to prevent from triggering so that self is accessible via the gesture recognizer’s selector method you’ll be attaching to the alert (self in the selector insinuates that all of this is inside a view controller).

lazy var alert: UIAlertController = {

    let alert = UIAlertController(title: "Title", message: "Message", preferredStyle: .alert)

    alert.addTextField(configurationHandler: nil)

    let appendAction = self.appendAction
    let cancelAction = UIAlertAction(title: "Cancel", style: .cancel, handler: nil)

    alert.addAction(appendAction)
    alert.addAction(cancelAction)

    let gestureRecognizer = UILongPressGestureRecognizer(target: self, action: #selector(append(sender:)))
    gestureRecognizer.minimumPressDuration = 0.0
    alert.view.addGestureRecognizer(gestureRecognizer)

    return alert
}()

lazy var appendAction: UIAlertAction = {
    return UIAlertAction(title: "Paste Message", style: .default, handler: nil)
}()

Make sure your gesture recognizer above is a UILongPressGestureRecognizer set with a minimum press duration of 0. That way you can access the state of the gesture (for when the user touches down) before the action is triggered fully. There you can disable the UIAlertAction, implement your custom code, and reenable the action after the gesture has completed (user has touched up). See below:

@objc func append(sender: UILongPressGestureRecognizer) {
    
    switch sender.state {
    case .began:
        appendAction.isEnabled = false
    case .ended:
        // Do whatever you want with the alert text fields
        print(alert.textFields?[0].text)
        appendAction.isEnabled = true
    default:
        return
    }
}

Also, make sure that the view controller owning the presentation of this alert conforms to UIGestureRecognizerDelegate in order to recognize simultaneous gestures.

extension YourViewController: UIGestureRecognizerDelegate {

    func gestureRecognizer(_ gestureRecognizer: UIGestureRecognizer, shouldRecognizeSimultaneouslyWith otherGestureRecognizer: UIGestureRecognizer) -> Bool {
        return true
    }
}

Then, just present the UIAlertController wherever.

func showAlert() {
    self.present(alert, animated: true, completion: nil)
}

This is obviously a hack, but there’s no other way that I know to achieve this without a hack since it’s not meant to be achieved. For example, the gesture recognizer is tied to the UIAlertController so the user can trigger that method if they tap anywhere on the alert (besides the cancel button).

ORIGINAL ANSWER:

This is as close as I could come to a hack-a-round. If there was some way to customize the dismissal transition time to nothing then you could set animated: to false and it would look like the same alert, but I don’t think it’s possible

class ViewController: UIViewController {

    @IBAction func alert(sender: AnyObject) {
        let alert = UIAlertController(title: "title", message: "message", preferredStyle: .Alert)
    
        alert.addTextFieldWithConfigurationHandler(nil)
    
        let appendAction = UIAlertAction(title: "Append text", style: .Default) { _ in
            var textField = alert.textFields![0] as UITextField
            // Append text here
            self.presentViewController(alert, animated: true, completion: nil)
        }
    
        let cancelAction = UIAlertAction(title: "Cancel", style: .Cancel, handler: nil)
    
        alert.addAction(appendAction)
        alert.addAction(cancelAction)
    
        self.presentViewController(alert, animated: true, completion: nil)
    }
}

I’m only familiar with swift