myhomie_app/lib/Screens/Home/HomePage.dart

import 'package:flutter/material.dart';
import 'package:flutter/rendering.dart';
import 'package:flutter/services.dart';
import 'package:mqtt_client/mqtt_client.dart';
import 'package:mqtt_client/mqtt_server_client.dart';
import 'package:mycoreapi/api.dart';
import 'package:myhomie_app/Helpers/MQTTHelper.dart';
import 'package:myhomie_app/Screens/Debug/DebugPage.dart';
import 'package:myhomie_app/app_context.dart';
import 'package:myhomie_app/client.dart';
import 'package:provider/provider.dart';

class HomePage extends StatefulWidget {
  HomePage({Key key}) : super(key: key);

  @override
  _HomePageState createState() => _HomePageState();
}

class _HomePageState extends State<HomePage> {
  int _counter = 0;
  final MqttServerClient client = MqttServerClient.withPort('192.168.31.140', 'flutter_client', 1883); // TODO Add switch button or check online connexion if local broker available
  //final MqttServerClient client = MqttServerClient.withPort('myhomie.be', 'flutter_client00', 1883); // TODO ONLINE

  void _incrementCounter() {
    setState(() {
      _counter++;
      
      print("client.connectionStatus !!! ==" + client.connectionStatus.toString());
      if (client.connectionStatus.state == MqttConnectionState.connected) {
        const pubTopic = 'topic/test';
        final builder = MqttClientPayloadBuilder();
        builder.addString('Hello MQTT');
        client.publishMessage(pubTopic, MqttQos.atLeastOnce, builder.payload);
      }
    });
  }

  // connection succeeded
  void onConnected() {
    print('Connected !!!!!!!!!!!! ----------------------------------');

    client.updates.listen((List<MqttReceivedMessage<MqttMessage>> c) {
      final MqttPublishMessage message = c[0].payload;
      final payload = MqttPublishPayload.bytesToStringAsString(message.payload.message);
      print('Received message:$payload from topic: ${c[0].topic}>');
    });
  }

// unconnected
  void onDisconnected() {
    print('Disconnected');
  }

// subscribe to topic succeeded
  void onSubscribed(String topic) {
    print('Subscribed topic: $topic');
  }

// subscribe to topic failed
  void onSubscribeFail(String topic) {
    print('Failed to subscribe $topic');
  }

// unsubscribe succeeded
  void onUnsubscribed(String topic) {
    print('Unsubscribed topic: $topic');
  }

  Future<MqttServerClient> connect() async {
    client.logging(on: false);
    client.keepAlivePeriod = 20;
    client.onDisconnected = onDisconnected;
    client.onConnected = onConnected;
    client.onSubscribed = onSubscribed;

    /// Security context
    /*SecurityContext context = new SecurityContext()
      ..useCertificateChain('path/to/my_cert.pem')
      ..usePrivateKey('path/to/my_key.pem', password: 'key_password')
      ..setClientAuthorities('path/to/client.crt', password: 'password');*/
    //client.setProtocolV31();
    //client.secure = true;
    //client.securityContext = context;

    final connMessage = MqttConnectMessage()
        .authenticateAs('thomas', 'MyCore,1') // TODO ONLINE
     /*.keepAliveFor(60)
    .withWillTopic('willtopic')
        .withWillMessage('Will message')*/
    .withClientIdentifier("TESSST")
        .startClean();
        //.withWillQos(MqttQos.atLeastOnce);
    //client.secure = true;
    client.connectionMessage = connMessage;
    client.autoReconnect = true;
    try {
      await client.connect();
    } catch (e) {
      print('Exception: $e');
      client.disconnect();
    }

    client.subscribe("#", MqttQos.atLeastOnce);

    return client;
    return null;
  }

  @override
  Widget build(BuildContext context) {
    final appContext = Provider.of<AppContext>(context);

    if (!MQTTHelper.instance.isInstantiated)
    {
      print("MQTT NOT INSTANTIATED");
      MQTTHelper.instance.connect(appContext);
    }


    return Scaffold(
      appBar: AppBar(
        title: Text("HomePage TODO"),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text(
              'You have pushed the button this many times:',
            ),
            Text(
              '$_counter',
              style: Theme.of(context).textTheme.headline4,
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: () => {
          Navigator.push(
              context,
              MaterialPageRoute(
                builder: (context) {
                  return DebugPage();
                },
              )
          )
        },
        tooltip: 'Increment',
        child: Icon(Icons.add),
      ),
    );
  }
}