porcupine_manager.dart

 PorcupineManager porcupineManager;

  /// Create an instance of your porcupineManager which will listen for the given wake words
  /// Must call start on the manager to actually start listening
  void createPorcupineManager() async {
    try{
      porcupineManager = await PorcupineManager.fromKeywords(
         Porcupine.BUILT_IN_KEYWORDS,
          wakeWordCallback);
    } on PvError catch (err) {
      // handle porcupine init error
      print('Porcupine error: '+ err.message);
    }
  }

  /// The function that's triggered when the Porcupine instance recognizes a wake word
  /// Input is the index of the wake word in the list of those being used
  void wakeWordCallback(int word){
    print('Wake word index: '+ word.toString());
  }

/// Begin listening for a wake word
  void listenForWakeWord() async{
    try{
      await porcupineManager.start();
    } on PvAudioException catch (ex) {
      // deal with either audio exception     
      print('PvAudioException: '+ ex.message);
    }
  }