My function in my main view controller is not working - xcode

Question

I´m trying to use a function that I wrote in my main viewController, this is it.
func displayAlert(title: String, message: String)
{
let alert = UIAlertController(title: title, message: message, preferredStyle: UIAlertControllerStyle.Alert)
alert.addAction((UIAlertAction(title: "Ok", style: .Default, handler:
{ (action) -> Void in
self .dismissViewControllerAnimated(true, completion: nil)
})))
self.presentViewController(alert, animated: true, completion: nil)
}
I´m trying to use it on other viewController call viewControllerRegistro, for some reason is not working. this is it...
#IBAction func signUp(sender: AnyObject)
{
//checar que el usuario copero al poner su correo electronico y su contraseña
if usernameRegistro.text == "" || correoRegistro.text == "" || contraseñaRegistro.text == ""
{
ViewController().displayAlert("Informando Error", message: "Porfavor completa los cuadros de registro")
}
any help?
I´m using xcode 7.0 beta 6 with swift 2

Answer 1

ViewController() creates a new ViewController instance. That view controller is not part of your view hierarchy (because you just created it, without adding it anywhere).
You have to call that method on the view controller that is currently visible. Because of that the function should not be part of your MainViewController class. It should be part of the ViewController class that needs it. Or if you need it in multiple view classes you could add the function to an extension of UIViewController:
extension UIViewController {
func displayAlert(title: String, message: String) {
let alert = UIAlertController(title: title, message: message, preferredStyle: UIAlertControllerStyle.Alert)
alert.addAction((UIAlertAction(title: "Ok", style: .Default, handler:
{ (action) -> Void in
self .dismissViewControllerAnimated(true, completion: nil)
})))
presentViewController(alert, animated: true, completion: nil)
}
}
With this extension you can call displayAlert on any UIViewController and UIViewController subclasses.