Flutter之使用mqtt进行连接和信息传输的使用案例

目录

引言

什么是MQTT？

在Flutter中使用MQTT

安装

iOS 

安卓

创建一个全局的客户端对象

 配置客户端对象

 连接（异步）

监听接受的消息

发送消息 

监听连接状态和订阅的回调

---

引言

 随着移动应用开发技术的发展，实时通信成为了许多应用程序不可或缺的一部分。无论是社交应用中的即时消息传递，还是物联网(IoT)设备之间的数据交换，都需要一个高效稳定的通信机制。MQTT（Message Queuing Telemetry Transport）作为一种轻量级的消息协议，非常适合于这种场景。本文将介绍如何在Flutter项目中集成MQTT，并通过一个简单的示例来演示其基本用法。

什么是MQTT？

MQTT是一种基于发布/订阅模式的轻量级消息协议，设计初衷是为了提供低开销、低带宽的网络连接。它特别适合于远程位置的通信，如传感器与中央服务器之间的数据传输。MQTT的主要特点包括：

• 轻量级：非常小的代码占用空间和带宽使用。
• 发布/订阅模型：允许一对多的消息分发，即一个消息可以发送给多个客户端。
• 服务质量(QoS)：提供了三种不同的服务质量级别，以满足不同场景下的需求。
• 安全性：支持TLS/SSL加密，确保数据传输的安全性。

 

在Flutter中使用MQTT

首先需要安装mqtt_client这个依赖，执行下面命令

flutter pub add mqtt_client 

安装

如果您在 Android 或 iOS 设备上的 Flutter 环境中使用客户端，则需要进行以下设备权限设置。

iOS 

将以下键添加到位于ios/Runner/Info.plist的Info.plist文件中：

<key>NSLocalNetworkUsageDescription</key>
<string>Looking for local tcp Bonjour service</string>
<key>NSBonjourServices</key>
<array><string>mqtt.tcp</string>
</array>

安卓

将以下 Android 权限添加到位于android/app/src/main/AndroidManifest.xml的AndroidManifest.xml文件中：

<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />

在页面中导入：

import 'package:mqtt_client/mqtt_client.dart';

使用案例， 这里我们使用的是wss协议：

import 'dart:convert';
import 'package:flutter_diancan/utils/logger_helper.dart';
import 'package:mqtt_client/mqtt_client.dart';
import 'package:mqtt_client/mqtt_server_client.dart';
import 'package:shared_preferences/shared_preferences.dart';class MqttServe {final client = MqttServerClient('请求地址', '');Future<MqttClient> connect() async {try {client.setProtocolV311();client.logging(on: true);client.port = 443; // 端口号client.keepAlivePeriod = 60;client.websocketProtocols = ['mqtt'];client.useWebSocket = true;  // 因为我们这里使用的是wss协议所以加这个，这个根据自己的需求来定是否需要client.onConnected = onConnected;client.onDisconnected = onDisconnected;client.onUnsubscribed = onUnsubscribed;client.onSubscribed = onSubscribed;client.onSubscribeFail = onSubscribeFail;client.pongCallback = pong;client.connectTimeoutPeriod = 60;final connMess = MqttConnectMessage().authenticateAs("用户名", "密码").withClientIdentifier('Mqtt_MyClientUniqueId').withWillTopic('willtopic').withWillMessage('My Will message').startClean().withWillQos(MqttQos.atLeastOnce);client.connectionMessage = connMess;try {print('Connecting');await client.connect();} catch (e) {print('Exception: $e');client.disconnect();}client.updates!.listen((List<MqttReceivedMessage<MqttMessage?>>? c) async {final recMessage = c![0].payload as MqttPublishMessage;final payload = MqttPublishPayload.bytesToStringAsString(recMessage.payload.message);print('Received message:$payload from topic: ${c[0].topic}');});} catch (e, s) {LoggerHelper.fatal(e, s);}return client;}Future<void> sendMessage() async {if (client.connectionStatus?.state == MqttConnectionState.connected) {final builder = MqttClientPayloadBuilder();var payloadObject = {'MsgData': "发送成功啦"};print("发送的信息:${json.encode(payloadObject)} ");builder.addUTF8String(json.encode(payloadObject));client.publishMessage('发送消息的订阅地址', MqttQos.atLeastOnce, builder.payload!);}}// Connected callbackvoid onConnected() {print("已连接");try {// 连接后订阅client.subscribe('订阅地址', MqttQos.atLeastOnce);} catch (e, s) {LoggerHelper.fatal(e, s);}}// Disconnected callbackvoid onDisconnected() async {print('已断开');final SharedPreferences prefs = await SharedPreferences.getInstance();String? token = prefs.getString('token');if (token != null) {reconnect();}}Future<void> reconnect() async {print("重连中");int retryCount = 0;const maxRetries = 10;const baseRetryInterval = 2; // 初始重连间隔时间（秒）while (retryCount < maxRetries) {try {print('Reconnecting attempt ${retryCount + 1}...');await client.connect();if (client.connectionStatus?.state == MqttConnectionState.connected) {print('Reconnected successfully.');break;}} catch (e) {print('Reconnect failed: $e');}// 计算下一次重连间隔时间（指数退避）int retryInterval = baseRetryInterval * (2 << retryCount);await Future.delayed(Duration(seconds: retryInterval));retryCount++;}}// 关闭Future<void> close() async {try {// 重新订阅client.unsubscribe('订阅地址');} catch (e, s) {LoggerHelper.fatal(e, s);}client.disconnect();}// Subscribed callbackvoid onSubscribed(String topic) {print('订阅成功，主题为: $topic');}// Subscribed failed callbackvoid onSubscribeFail(String topic) {print('订阅失败，主题为: $topic');}// Unsubscribed callbackvoid onUnsubscribed(String? topic) {print('Unsubscribed topic: $topic');}// Ping callbackvoid pong() {print('调用Ping响应客户端回调');}
}

• 创建一个全局的客户端对象

final client = MqttServerClient('请求地址', '');

•  配置客户端对象

      client.setProtocolV311();client.logging(on: true);client.port = 443; // 端口号client.keepAlivePeriod = 60;client.websocketProtocols = ['mqtt'];client.useWebSocket = true;  // 因为我们这里使用的是wss协议所以加这个，这个根据自己的需求来定是否需要client.onConnected = onConnected;client.onDisconnected = onDisconnected;client.onUnsubscribed = onUnsubscribed;client.onSubscribed = onSubscribed;client.onSubscribeFail = onSubscribeFail;client.pongCallback = pong;client.connectTimeoutPeriod = 60;

• 设置连接消息

 final connMess = MqttConnectMessage().authenticateAs("用户名", "密码").withClientIdentifier('Mqtt_MyClientUniqueId').withWillTopic('willtopic').withWillMessage('My Will message').startClean().withWillQos(MqttQos.atLeastOnce);client.connectionMessage = connMess;

•  连接（异步）

 try {print('Connecting');await client.connect();} catch (e) {print('Exception: $e');client.disconnect();}

• 监听接受的消息

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

• 发送消息 

Future<void> sendMessage() async {if (client.connectionStatus?.state == MqttConnectionState.connected) {final builder = MqttClientPayloadBuilder();var payloadObject = {'MsgData': "发送成功啦"};print("发送的信息:${json.encode(payloadObject)} ");builder.addUTF8String(json.encode(payloadObject));client.publishMessage('发送消息的订阅地址', MqttQos.atLeastOnce, builder.payload!);}}

• 监听连接状态和订阅的回调

// Connected callbackvoid onConnected() {print("已连接");try {// 连接后订阅client.subscribe('订阅地址', MqttQos.atLeastOnce);} catch (e, s) {LoggerHelper.fatal(e, s);}}// Disconnected callbackvoid onDisconnected() async {print('已断开');final SharedPreferences prefs = await SharedPreferences.getInstance();String? token = prefs.getString('token');if (token != null) {reconnect();}}Future<void> reconnect() async {print("重连中");int retryCount = 0;const maxRetries = 10;const baseRetryInterval = 2; // 初始重连间隔时间（秒）while (retryCount < maxRetries) {try {print('Reconnecting attempt ${retryCount + 1}...');await client.connect();if (client.connectionStatus?.state == MqttConnectionState.connected) {print('Reconnected successfully.');break;}} catch (e) {print('Reconnect failed: $e');}// 计算下一次重连间隔时间（指数退避）int retryInterval = baseRetryInterval * (2 << retryCount);await Future.delayed(Duration(seconds: retryInterval));retryCount++;}}// 关闭Future<void> close() async {try {// 重新订阅client.unsubscribe('订阅地址');} catch (e, s) {LoggerHelper.fatal(e, s);}client.disconnect();}// Subscribed callbackvoid onSubscribed(String topic) {print('订阅成功，主题为: $topic');}// Subscribed failed callbackvoid onSubscribeFail(String topic) {print('订阅失败，主题为: $topic');}// Unsubscribed callbackvoid onUnsubscribed(String? topic) {print('Unsubscribed topic: $topic');}// Ping callbackvoid pong() {print('调用Ping响应客户端回调');}