I'm having trouble connecting to mqtt in flutter? - flutter

Question

I'm having trouble connecting to mqtt in flutter. I can't connect. The code I am using is as follows.
import 'package:mqtt_client/mqtt_server_client.dart';
late MqttServerClient client;
// ignore: camel_case_types
class mqttconnect {
Future<MqttServerClient> connect() async {
try {
client =
MqttServerClient.withPort('broker.emqx.io', 'flutter_client', 1883);
client.logging(on: true);
client.onConnected = onConnected;
client.onDisconnected = onDisconnected;
} catch (e) {
print(e.toString());
}
try {
await client.connect();
} catch (e) {
print('Exception: $e');
client.disconnect();
}
return client;
}
void onConnected() {
print('object');
}
void onDisconnected() {}
}
While trying to connect to mqtt, I get an error as above in the console. How can I fix.

Answer 1

import 'dart:convert';
import 'dart:developer';
import 'package:mqtt_client/mqtt_client.dart';
import 'package:mqtt_client/mqtt_server_client.dart';
late MqttServerClient client;
mqttSubscribe() async {
client = MqttServerClient.withPort("broker.emqx.io", "daly", 1883);
client.keepAlivePeriod = 30;
client.autoReconnect = true;
await client.connect().onError((error, stackTrace) {
log("error -> " + error.toString());
});
client.onConnected = () {
log('MQTT connected');
};
client.onDisconnected = () {
log('MQTT disconnected');
};
client.onSubscribed = (String topic) {
log('MQTT subscribed to $topic');
};
if (client.connectionStatus!.state == MqttConnectionState.connected) {
client.subscribe("battery", MqttQos.atMostOnce);
client.updates!.listen((List<MqttReceivedMessage<MqttMessage?>>? c) {
final recMess = c![0].payload as MqttPublishMessage;
final pt = MqttPublishPayload.bytesToStringAsString(recMess.payload.message);
log("message payload => " + pt);
});
}
}

Answer 2

import 'dart:async';
import 'package:mqtt_client/mqtt_client.dart';
import 'package:mqtt_client/mqtt_server_client.dart';
class MqttService{
MqttService._();
/// Our mqtt client object.
static late MqttClient client;
// for listen from other pages.
// and can close listen mqtt.
static StreamSubscription? mqttListen;
static void initMqtt(){
/// Initialize Mqtt and connect.
client = MqttServerClient(/* Your mqtt host address */)
..logging(on: false)
..port = MqttConstants.mqttPort
..keepAlivePeriod = 20
..onDisconnected = _onDisconnected
..onSubscribed = _onSubscribed
..onConnected = _onConnected
..onUnsubscribed = _onUnsubscribed
..onSubscribeFail = _onSubscribeFail;
/// If the mqtt connection lost
/// MqttBroker publish this message on this topic.
final mqttMsg = MqttConnectMessage()
.withWillMessage('connection-failed')
.withWillTopic('willTopic')
.startClean()
.withWillQos(MqttQos.atLeastOnce)
.withWillTopic('failed');
client.connectionMessage = mqttMsg;
await _connectMqtt();
}
/// Mqtt server connected.
void _onConnected() {
log('Connected');
_listenMqtt();
}
/// Mqtt server disconnected
void _onDisconnected() {
log('Disconnected');
}
/// Mqtt server subscribed
void _onSubscribed(String? topic) {
log('Subscribed topic is : $topic');
}
void _onUnsubscribed(String? topic) {
log('Unsubscribed topic is : $topic');
}
void _onSubscribeFail(String? topic) {
log('Failed subscribe topic : $topic');
}
/// Connection MQTT Server.
Future<void> _connectMqtt() async {
if (client.connectionStatus!.state != MqttConnectionState.connected) {
try {
await client.connect();
} catch (e) {
log('Connection failed' + e.toString());
}
} else {
log('MQTT Server already connected ');
}
}
/// Diconnection MQTT Server.
static Future<void> disconnectMqtt() async {
if (client.connectionStatus!.state == MqttConnectionState.connected) {
try {
client.disconnect();
} catch (e) {
log('Disconnection Failed ' + e.toString());
}
} else {
log('MQTT Server already disconnected ');
}
}
/// Subscribe a topic
static void subscribeTopic(String topic) {
final state = client.connectionStatus?.state;
if (state != null) {
if (state == MqttConnectionState.connected) {
client.subscribe(topic + "/data", MqttQos.atLeastOnce);
}
}
}
/// Publish a message to topic
/// [reatain] means last message save the broker.
static void publish(String topic, String message, {bool retain = true}) {
final builder = MqttClientPayloadBuilder();
builder.addString(message);
client.publishMessage(
topic,
MqttQos.atLeastOnce,
builder.payload!,
retain: retain,
);
builder.clear();
}
static void unSubscribeTopic(String topic) {
final state = client.connectionStatus?.state;
if (state != null) {
if (state == MqttConnectionState.connected) {
client.unsubscribe(topic + "/data");
}
}
}
static void onClose(){
mqttListen?.close();
disconnectMqtt();
}
void _listenMqtt() {
mqttListen = client.updates!.listen((dynamic t) {
MqttPublishMessage recMessage = t[0].payload;
final message =
MqttPublishPayload.bytesToStringAsString(recMessage.payload.message);
/*
Listen subscribe topic.
*/
log(message);
});
}
}
I have created a nice format for MQTT and I wanted to share with you through this question.
Package: mqtt_client