Just a boiler plate code to display simple alert in Swift.

simpleAlert.swift

let alert = UIAlertController(title: "Simple Title", 
                              message: "Alert message", 
                              preferredStyle: .alert)
let okAction = UIAlertAction(title: "Close", style: .default)
alert.addAction(okAction)
DispatchQueue.main.async {
  UIApplication.topViewController()?.present(alert, animated: true, completion: nil)
}