Update Custom-Voice-Controller example (#152)

Check #133 (comment) for more info.

Author: S2Ler

Navigation-Examples/Examples/Custom-Voice-Controller.swift

@@ -1,3 +1,9 @@
+/*
+ This code example is part of the Mapbox Navigation SDK for iOS demo app.
+ To learn more about each example in this app, including descriptions and links
+ to documentation, see our docs: https://docs.mapbox.com/ios/navigation/examples/custom-voice-controller/
+ */
+
 import Foundation
 import UIKit
 import MapboxCoreNavigation
@@ -20,33 +26,47 @@ class CustomVoiceControllerUI: UIViewController {
             case .failure(let error):
                 print(error.localizedDescription)
             case .success(let response):
-                guard let strongSelf = self else {
-                    return
-                }
-                
-                // For demonstration purposes, simulate locations if the Simulate Navigation option is on.
-                let navigationService = MapboxNavigationService(routeResponse: response, routeIndex: 0, routeOptions: routeOptions, simulating: simulationIsEnabled ? .always : .onPoorGPS)
-                
-                // `MultiplexedSpeechSynthesizer` will provide "a backup" functionality to cover cases, which
-                // our custom implementation cannot handle.
-                let speechSynthesizer = MultiplexedSpeechSynthesizer([CustomVoiceController(), SystemSpeechSynthesizer()] as? [SpeechSynthesizing])
-                let routeVoiceController = RouteVoiceController(navigationService: navigationService, speechSynthesizer: speechSynthesizer)
-                // Remember to pass our `Voice Controller` to `Navigation Options`!
-                let navigationOptions = NavigationOptions(navigationService: navigationService, voiceController: routeVoiceController)
-                
-                let navigationViewController = NavigationViewController(for: response, routeIndex: 0, routeOptions: routeOptions, navigationOptions: navigationOptions)
-                navigationViewController.modalPresentationStyle = .fullScreen
-                
-                strongSelf.present(navigationViewController, animated: true, completion: nil)
+                self?.presentNavigationWithCustomVoiceController(routeOptions: routeOptions, response: response)
             }
         }
     }
+
+    func presentNavigationWithCustomVoiceController(routeOptions: NavigationRouteOptions, response: RouteResponse) {
+        // For demonstration purposes, simulate locations if the Simulate Navigation option is on.
+        let navigationService = MapboxNavigationService(routeResponse: response,
+                                                        routeIndex: 0,
+                                                        routeOptions: routeOptions,
+                                                        simulating: simulationIsEnabled ? .always : .onPoorGPS)
+
+        // `MultiplexedSpeechSynthesizer` will provide "a backup" functionality to cover cases, which
+        // our custom implementation cannot handle.
+        let speechSynthesizer = MultiplexedSpeechSynthesizer([CustomVoiceController(), SystemSpeechSynthesizer()])
+
+        // Create a `RouteVoiceController` type with a customized `SpeechSynthesizing` instance.
+        // A route voice controller monitors turn-by-turn navigation events and triggers playing spoken instructions
+        // as audio using the custom `speechSynthesizer` we created above.
+        let routeVoiceController = RouteVoiceController(navigationService: navigationService,
+                                                        speechSynthesizer: speechSynthesizer)
+        // Remember to pass our RouteVoiceController` to `Navigation Options`!
+        let navigationOptions = NavigationOptions(navigationService: navigationService,
+                                                  voiceController: routeVoiceController)
+
+        // Create `NavigationViewController` with the custom `NavigationOptions`.
+        let navigationViewController = NavigationViewController(for: response,
+                                                                routeIndex: 0,
+                                                                routeOptions: routeOptions,
+                                                                navigationOptions: navigationOptions)
+        navigationViewController.modalPresentationStyle = .fullScreen
+
+        present(navigationViewController, animated: true, completion: nil)
+    }
 }
 
 class CustomVoiceController: MapboxSpeechSynthesizer {
 
     // You will need audio files for as many or few cases as you'd like to handle
-    // This example just covers left and right. All other cases will fail the Custom Voice Controller and force a backup System Speech to kick in
+    // This example just covers left and right. All other cases will fail the Custom Voice Controller and
+    // force a backup System Speech to kick in
     let turnLeft = NSDataAsset(name: "turnleft")!.data
     let turnRight = NSDataAsset(name: "turnright")!.data