如何在 flutter 中将数据以 JSON 形式发送到 MQTT 代理

Question

    return RaisedButton(
      color: Colors.green,
      disabledColor: Colors.grey,
      textColor: Colors.white,
      disabledTextColor:Colors.black38 ,
      child: Text("Break"),
      onPressed: state == MQTTAppConnectionState.connectedSubscribed
          ? () {
        setState(() {
          value = 0;
          action = jsonData;
        });
        publishMessage(action);
      }
          : null, //
    );
  }

I have multiple buttons in my app that passes different message  to mqtt client


I want to pass  different json data to mqtt client for each button 


sample json data for single button 

{ "电机":"BLDC电机", “ACC”：70， “F/R”：“前进”， "Break":"假", “关键”：“真实” 端

按下按钮时帮助我将单个 json 数据传递给 mqtt 客户

Answer 1

在发布方法中传递值并进行更改，它将起作用

return RaisedButton(
  color: Colors.green,
  disabledColor: Colors.grey,
  textColor: Colors.white,
  disabledTextColor:Colors.black38 ,
  child: Text("Break"),
  onPressed: state == MQTTAppConnectionState.connectedSubscribed
      ? () {
    setState(() {
      break1 = "True";
      value = 0;
    });
    publish(break1);
  }
      : null,//
);

void publish(String break1) {
final MqttClientPayloadBuilder builder = MqttClientPayloadBuilder();
builder.addString(
  json.encode(
    {
      "break": "$break1",
    }
  )
);
_client!.publishMessage(_topic, MqttQos.exactlyOnce, builder.payload!);}