How to Send data as JSON over to MQTT broker in flutter

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 

{ "Motor":"BLDC motor", "Acc": 70, "F/R": "Forward", "Break":"False", "Key":"True" }

help me to pass single json data to mqtt client when the button is pressed

Answer 1

Pass the values in the publish method and make this changes there it will work

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!);}