How to convert MQTT Message to JSON format in Flutter - json

Question

I already connect and get data from MQTT broker using snapshot method. However, I want to convert the MQTT message to JSON format cause I want to do some condition code to certain data.
My problem is when I stream data from the MQTT broker, my data only came out for the last data for that index. That index consists three different data, but since the index hold 3 data at the same time, only the last data of the index that displayed. This is my current code. How can I do that?
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text("Flutter MQTT"),
),
body: FutureBuilder(
future: mqttSubscribe(topic: "/sensor_simulator/data"),
builder: (BuildContext context, AsyncSnapshot snapshot) {
if (snapshot.hasError) {
return Center(
child: Text("Error: ${snapshot.error}"),
);
}
// if succeed to connect
if (snapshot.connectionState == ConnectionState.done) {
return StreamBuilder(
stream: snapshot.data,
builder: (BuildContext context, AsyncSnapshot snapshot) {
// if have error--> display
if (snapshot.hasError) {
return Center(
child: Text("Error: ${snapshot.error}"),
);
}
// if data detected--> display
if (snapshot.hasData) {
try {
final List<MqttReceivedMessage> receiveMessage =
snapshot.data;
final recMess =
receiveMessage[0].payload as MqttPublishMessage;
String payload = MqttPublishPayload.bytesToStringAsString(
recMess.payload.message);
return ListView(
children: [
Card(
child: ListTile(
title: Text(payload),
))
],
padding: EdgeInsets.all(10),
);
} catch (e) {
return Center(
child: Text("Error: ${e.toString()}"),
);
}
}
return Center(child: CircularProgressIndicator());
},
);
}
return Center(child: CircularProgressIndicator());
},
),
);
}
}

Answer 1

You can use this piece of code:
void _subscribeToTopic(String topicName) {
print('MQTTClientWrapper::Subscribing to the $topicName topic');
client.subscribe(topicName, MqttQos.atMostOnce);
client.updates!.listen((List<MqttReceivedMessage<MqttMessage>> c) {
final recMess = c[0].payload as MqttPublishMessage;
String message =
MqttPublishPayload.bytesToStringAsString(recMess.payload.message);
String decodeMessage = Utf8Decoder().convert(message.codeUnits);
print("MQTTClientWrapper::GOT A NEW MESSAGE $decodeMessage");
});
}