Add voice guidance

_{Estimated reading time: 2 minutes}

For voice guidance we can use the flutter_tts package. Other packages for TTS can also be used. The voice instructions will come on the onTextToSpeechInstruction callback set during navigation or simulation.

Add flutter_tts as a dependency to the pubspec.yaml file of the project and run the dart pub get command to install the tts package.

We can use the onTextToSpeechInstruction callback of the startSimulation methods in the following way:

// instantiate FlutterTts
FlutterTts flutterTts = FlutterTts();

void simulationInstructionUpdated(NavigationInstruction instruction, Set<NavigationInstructionUpdateEvents> events) {
  // handle instruction
}

void textToSpeechInstructionUpdated(String ttsInstruction) {
  flutterTts.speak(ttsInstruction);
}

TaskHandler? taskHandler = NavigationService.startSimulation(
  route,
  null,
  onNavigationInstruction: simulationInstructionUpdated,
  onTextToSpeechInstruction: textToSpeechInstructionUpdated,
  speedMultiplier: 2,
);

For navigation we can set the onTextToSpeechInstruction callback in a similar way with startNavigation.

Text to speech instructions language

The TTS instruction strings will come in the language set using the SdkSettings.setTTSLanguage method. The snippet provided below sets the language to English. See the setting a map language for more info about the Language class.

Language lang = languages.where((lang) => lang.languagecode == 'eng' && lang.regioncode == 'GBR').first;
SdkSettings.setTTSLanguage(lang);

See the documentation for flutter_tts for information on how to set the TTS voice, language and other options such as pitch, volume, speechRate, etc.