Driving the Future of Connected Cars with MQTT →

Using MQTT in The Flutter Project

Zhiwei Yu
Jul 20, 2020
Using MQTT in The Flutter Project

Flutter is Google’s UI toolkit for building beautiful, natively compiled applications for mobile, web, and desktop from a single codebase. Flutter provides a rich set of components and interfaces, the developer can quickly add native expansion for Flutter. At the same time, Flutter also uses a Native engine to render view. There is no doubt that it can provide a good experience for users.

MQTT is a lightweight IoT communication protocol based on the publish/subscribe model. It can enable stable transmission over severely restricted device hardware and high-latency / low-bandwidth network. Because it is simple and easy to implement, supports QoS, and small size packet, it occupies half market of the Internet of Things protocol.

This article mainly introduces how to use MQTT in the Flutter project to implement the connection between the client and MQTT broker, subscribe, unsubscribe, send and receive messages, and other functions.

Learn more: How to use MQTT on Android.

Project Initialization

Create a project

Create a new project, can refer to the following links:

Install dependencies

Add dependencies into file pubspec.yaml

  mqtt_client: ^7.2.1

Install dependencies:

flutter pub get


import 'package:mqtt_client/mqtt_client.dart';

Use of MQTT

Connect to MQTT broker

This article will use the MQTT broker which is operated and maintained by EMQX Cloud. EMQX Cloud is the MQTT IoT cloud service platform released by EMQ, it provides the service for accessing MQTT 5.0 with all-in-one operation and maintenance and unique isolation environment.

  • Broker: broker.emqx.io
  • TCP Port: 1883
  • Websocket Port: 8083

Open Manufacturing Hub
A Practical Guide to MQTT Broker Selection
Download this practical guide and learn what to consider when choosing an MQTT broker.
Get the eBook →

The example of connect

Future<MqttServerClient> connect() async {
  MqttServerClient client =
      MqttServerClient.withPort('broker.emqx.io', 'flutter_client', 1883);
  client.logging(on: true);
  client.onConnected = onConnected;
  client.onDisconnected = onDisconnected;
  client.onUnsubscribed = onUnsubscribed;
  client.onSubscribed = onSubscribed;
  client.onSubscribeFail = onSubscribeFail;
  client.pongCallback = pong;

  final connMessage = MqttConnectMessage()
      .authenticateAs('username', 'password')
      .withWillMessage('Will message')
  client.connectionMessage = connMessage;
  try {
    await client.connect();
  } catch (e) {
    print('Exception: $e');

  client.updates.listen((List<MqttReceivedMessage<MqttMessage>> c) {
    final MqttPublishMessage message = c[0].payload;
    final payload =

    print('Received message:$payload from topic: ${c[0].topic}>');

  return client;

The description of the callback method

// connection succeeded
void onConnected() {

// unconnected
void onDisconnected() {

// 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');

// PING response received
void pong() {
  print('Ping response client callback invoked');

MqttConnectMessage: set connection options, including timeout settings, authentication, last wish messages, etc.

client.updates.listen: used for monitoring the arrival of messages of the subscribed topics

The example of certificate connection

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

Other MQTT operations

Subscribe to topic

client.subscribe("topic/test", MqttQos.atLeastOnce)

Publish message

const pubTopic = 'topic/test';
final builder = MqttClientPayloadBuilder();
builder.addString('Hello MQTT');
client.publishMessage(pubTopic, MqttQos.atLeastOnce, builder.payload);






We write a simple UI interface for this project and use MQTT 5.0 client tool - MQTTX to do the following tests:

  • connect

  • subscribe

  • publish

  • unsubscribe

  • disconnect

The interface of the application:


Use MQTTX as another client to send and receive messages:


We can see the log of the whole process



So far, we have finished that use Flutter to build MQTT applications in the Android platform, implemented the connection between the client and MQTT broker, subscribe, unsubscribe, publish and receive messages, etc.

Flutter makes it easy that develop powerful mobile applications through unified programming language and the feature cross-platform. It may be the most proper solution for developing mobile applications in the future. Using Flutter, MQTT protocol and MQTT cloud service, we can develop more interesting applications.

Next, you can check out The Easy-to-understand Guide to MQTT Protocol series of articles provided by EMQ to learn about MQTT protocol features, explore more advanced applications of MQTT, and get started with MQTT application and service development.

Try EMQX Cloud for Free
No credit card required
Get Started →

Related Posts

Oct 29, 2020Shifan Yu
How to use MQTT in the Electron project

This article introduces how to use MQTT in the Electron project, and implement the connection, subscription and messaging, etc of MQTT.

Nov 15, 2022Zhiwei Yu
How to Use MQTT in Dart

This article introduces how to use MQTT in the Dart project, and implements the connection, subscription and messaging, etc of MQTT.

Jun 16, 2020Zhiwei Yu
Android and MQTT: Step by Step Guide

This article introduces how to use MQTT to implement the connection, messaging, etc between Android client and MQTT broker, through using Kotlin.