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长沙的网站建设公司,青岛seo关键词排名,新风格网站,网站建设要解决哪些方面的事项目录引言什么是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…

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');}

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