Flutter中使用mqtt_client实现发布topic1并监听topic2可行吗？

• 区分发布与监听的主题配置
  由于现在发布和监听的主题不同，需要将两者分开存储。你可以修改MQTTManager的构造函数，新增对应参数来支持动态配置：

  MQTTManager(
      {required String host,
      required String publishTopic,
      required String listenTopic,
      required String identifier,
      required MQTTAppState state})
      : _identifier = 'id',
        _host = '48.38.96.88',
        _publishTopic = publishTopic,
        _listenTopic = listenTopic,
        _currentState = state;
  

  如果暂时不需要动态配置，也可以直接硬编码主题：

  // 替换原有的单一_topic定义
  final String _publishTopic = 'topic1';
  final String _listenTopic = 'topic2';
  

• 修改连接成功后的订阅逻辑
  在onConnected方法中，将订阅的主题从原来的topic1改为topic2：

  void onConnected() {
    _currentState.setAppConnectionState(MQTTAppConnectionState.connected);
    print('EXAMPLE::Mosquitto client connected....');
    // 订阅监听topic2
    _client!.subscribe(_listenTopic, MqttQos.atLeastOnce);
    _client!.updates!.listen((List<MqttReceivedMessage<MqttMessage?>>? c) {
      final MqttPublishMessage recMess = c![0].payload as MqttPublishMessage;
      final String pt =
          MqttPublishPayload.bytesToStringAsString(recMess.payload.message!);
      _currentState.setReceivedText(pt);
      print(
          'EXAMPLE::Change notification:: topic is <${c[0].topic}>, payload is <-- $pt -->');
      print('');
    });
    print(
        'EXAMPLE::OnConnected client callback - Client connection was sucessful');
  }
  

• 确保消息发布到topic1
  找到你项目中发布消息的代码，确认发布目标是_publishTopic（即topic1），示例发布代码如下：

  void publishMessage(String message) {
    final MqttClientPayloadBuilder builder = MqttClientPayloadBuilder();
    builder.addString(message);
    _client!.publishMessage(
      _publishTopic,
      MqttQos.atLeastOnce,
      builder.payload!,
    );
  }
  

完成以上修改后，你的应用就能向topic1发布消息，同时监听topic2上的回复了。

内容的提问来源于stack exchange，提问作者Johan Scheepers