He escrito mi controlador de vista de alerta personalizado. Pero tengo un error al llamar a mi controlador de alerta desde otro controlador de vista. Me muestra el error que describí a continuación.

Error en la consola

2015-06-15 10:21:50.610 automobile[4197:62165] Warning: Attempt to present <UIAlertController: 0x7d11cf70> on <automobile.LoadingAlertViewController: 0x7bfa55d0> whose view is not in the window hierarchy!

Aquí está miLoadingAlertViewController

import UIKit

class LoadingAlertViewController: UIAlertController {

var loadingAlertController : UIAlertController!

override func viewDidLoad() {
    super.viewDidLoad()
}

override func didReceiveMemoryWarning() {
    super.didReceiveMemoryWarning()
    // Dispose of any resources that can be recreated.
}

func displayLoadingAlert() -> UIAlertController {

    var controllerToPresent = viewController
    if controllerToPresent == nil {
            controllerToPresent = self
    }
    //create an alert controller
    loadingAlertController = UIAlertController(title: "Loading...", message: "We are receiving data from network.Please Wait.", preferredStyle: .Alert)

    let indicator = UIActivityIndicatorView()
    indicator.color = UIColor.redColor()
    indicator.setTranslatesAutoresizingMaskIntoConstraints(false)
    loadingAlertController.view.addSubview(indicator)

    let views = ["pending" : loadingAlertController.view, "indicator" : indicator]
    var constraints = NSLayoutConstraint.constraintsWithVisualFormat("V:[indicator]-(7)-|", options: nil, metrics: nil, views: views)
    constraints += NSLayoutConstraint.constraintsWithVisualFormat("H:|[indicator]|", options: nil, metrics: nil, views: views)
    loadingAlertController.view.addConstraints(constraints)

    indicator.userInteractionEnabled = false
    indicator.startAnimating()

    controllerToPresent!.presentViewController(loadingAlertController, animated: true, completion: nil)

    return loadingAlertController
}

func dismissLoadingAlert() -> UIAlertController {
    loadingAlertController.dismissViewControllerAnimated(true, completion: nil)
    return loadingAlertController
}

}

Entonces decalore estoLoadingAlertViewController en mi otro controlador de vista donde quiero mostrar cada vez que solicito a mi API.

Este es miViewController.

import UIKit

class ViewController : UIViewControler{

var loadingAlertController : LoadingAlertController!
var api = MyAPI()

override func viewDidLoad() {

       loadingAlertController = LoadingAlertViewController()

       api.getResults()

       showAlert(true)

}

func showAlert(alert : Bool){

       if alert{

          loadingAlertController.displayLoadingAlert(self)

       }else{

          loadingAlertController.dismissLoadingAlert()

       }

}

¿Alguna ayuda? Por favor, si hay una manera, cómo llamarla desde otro controlador de vista. Gracias