警告：尝试在*视图不在窗口层次结构中的*上呈现UIAlertController - swift

Question

我收到此错误/警告，但没有找到任何答案。问题是我有两个代码文件： ViewController.swift 和 CoreLocationDelegate.swift 。

在下面的代码（CoreLocationDelegate.swift）中，您将找到 showLocationServicesDeniedAlert（）方法。在 getLocation（）中调用了哪个。

import UIKit
import CoreLocation

class CoreLocationDelegate: UIViewController, CLLocationManagerDelegate {

  // MARK: - CLLocationManagerDelegate

  let locationManager = CLLocationManager()

  func locationManager(manager: CLLocationManager, didFailWithError error: NSError) {
    print("didFailWithError: \(error)")
  }

  func locationManager(manager: CLLocationManager, didUpdateLocations locations: [CLLocation]) {
    let newLocation = locations.last!
    print("didUpdateLocations: \(newLocation)")
  }

  // MARK: getLocation method

  func getLocation() {

    // Check for current authorisation status of app:
    let authStatus = CLLocationManager.authorizationStatus()

    if authStatus == .NotDetermined {
      locationManager.requestAlwaysAuthorization()
      return
    }

    if authStatus == .Denied || authStatus == .Restricted {
      showLocationServicesDeniedAlert()
    }

    // Get current location
    locationManager.delegate = self
    locationManager.desiredAccuracy = kCLLocationAccuracyBestForNavigation
    locationManager.startUpdatingLocation()

  }

  func showLocationServicesDeniedAlert() {
    let alert = UIAlertController(title: "Location Services Disabled", message: "Please enable location services for this app in Settings.", preferredStyle: .Alert)

    let okAction = UIAlertAction(title: "OK", style: .Default, handler: nil)

    alert.addAction(okAction)

    presentViewController(alert, animated: true, completion: nil)
  }

}

现在，在以下代码（ViewController.swift）中的按钮内使用getLocation（）方法会出现问题：

import UIKit
import CoreLocation

    class ViewController: UIViewController, CLLocationManagerDelegate {

        @IBAction func getLocationButton(sender: AnyObject) {
            CoreLocationDelegate().getLocation()        
        }

    }

按下按钮时（在模拟器中）我得到警告：尝试在视图不在窗口层次结构中显示！

知道我缺少什么或需要掌握什么？