Alerts

UIAlertController displays an alert message in a small dialog box. Additionally you can associate an action with the alert controller.

let alert = UIAlertController.init(title: "Error", 
                                   message: "An unknown error has occurred", 
                                   preferredStyle: .alert)

let action = UIAlertAction.init(title: "Ok", 
                                style: .default) { _ in
   print("Ob button is pressed")
}

alert.addAction(action)
present(alert, animated: true, completion: nil)

extension UIViewController {
  
    func showErrorMessage(_ msg: String?) {
        let alert = UIAlertController(title: "Error",
                                      message:msg ?? "unknown error",
                                      preferredStyle: .alert)
        alert.addAction(UIAlertAction(title: "Ok",
                                      style: UIAlertAction.Style.default,
                                      handler: nil))
        present(alert, animated: true, completion: nil)
    }
    
    func showAlert(_ msg: String?, title: String? = nil) {
        let alert = UIAlertController(title: title ?? "Attention",
                                      message:msg ?? "unknown error",
                                      preferredStyle: .alert)
        alert.addAction(UIAlertAction(title: "Ok",
                                      style: .default,
                                      handler: nil))
        present(alert, animated: true, completion: nil)
    }
    
}

The alert may contain one or more text fields that allow the user to enter some data.

func showPromptAlert() {
    let alert = UIAlertController(title: "Enter text", 
                                  message: nil, 
                                  preferredStyle: .alert)
    
    alert.addTextField()
 
    let action = UIAlertAction(title: "Done", 
                               style: .default) { [unowned alert] _ in
        let textField = alert.textFields![0]
        // ...
    }

    alert.addAction(action)
    present(alert, animated: true)
}