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首先#xff0c;需要在Flutter项目的pubspec.yaml文件中添加mqtt_client依赖。
dependencies:#https://pub.dev/packages/mqtt_clientmqtt_client: ^10.0.02.创建MQTT客户端并连接到MQTT服务器:2.创建一个MQTT客户端实例来进行连接和通信
Fu…1.添加依赖:
首先需要在Flutter项目的pubspec.yaml文件中添加mqtt_client依赖。
dependencies:#https://pub.dev/packages/mqtt_clientmqtt_client: ^10.0.02.创建MQTT客户端并连接到MQTT服务器:2.创建一个MQTT客户端实例来进行连接和通信
FutureMqttServerClient connect(String cid) async {print(mqtt connect host $host cid $cid );MqttServerClient client MqttServerClient.withPort(host, cid, port);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(user, pwd).keepAliveFor(60)// 保持连接时间单位为秒.withWillTopic(willtopic).withWillMessage(Will message).startClean()// 清理会话.withWillQos(MqttQos.atLeastOnce);client.connectionMessage connMessage;try {await client.connect();} catch (e) {print(Exception: $e);client.disconnect();}return client;}其中host 是主机名port是端口号cid是客户端ID你可以根据需要为其分配一个唯一的标识。
3.订阅主题:
一旦连接到MQTT服务器你可以订阅感兴趣的主题以接收消息。以下是订阅主题的示例代码 //用于监听已订阅主题的消息到达。 client.updates?.listen((ListMqttReceivedMessageMqttMessage c) {final MqttPublishMessage recMess c[0].payload as MqttPublishMessage;final String pt MqttPublishPayload.bytesToStringAsString(recMess.payload.message);// 解码包含中文字符的字符串final String decodedString utf8.decode(pt.codeUnits);LogI(Received message: $decodedString from topic: ${c[0].topic});});通过client.subscribe方法订阅一个主题并使用client.updates流来监听接收到的消息。
4.发布消息:
使用MQTT客户端来发布消息到特定的主题。以下是发布消息的示例代码
final MqttClientPayloadBuilder builder MqttClientPayloadBuilder();
builder.addString(Hello from Flutter);client.publishMessage(your_topic, MqttQos.exactlyOnce, builder.payload);在上面的代码中使用MqttClientPayloadBuilder来构建消息的有效载荷然后使用client.publishMessage方法来发布消息到指定的主题。
5.断开连接:
当你不再需要与MQTT服务器通信时记得断开连接以释放资源
client.disconnect();完整代码
class XMqttClient {static final XMqttClient _instance XMqttClient._();static XMqttClient get instance _instance;static const host 139.196.xx.xx;//替换成你自己的主机static const port 1883;//端口号static const user admin;//用户static const pwd public;//密码ListString topics [];MqttClient? client;XMqttClient._() {_initMqtt();}_initMqtt() async {//clientld 确保唯一性否则如果两台机器的clientld 相同 则会连上立刻断开连接String clientId ${DateTime.now().millisecondsSinceEpoch}asc;client await connect(clientId);}FutureMqttServerClient connect(String cid) async {print(mqtt connect host $host cid $cid );MqttServerClient client MqttServerClient.withPort(host, cid, port);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(user, pwd).keepAliveFor(60)// 保持连接时间单位为秒.withWillTopic(willtopic).withWillMessage(Will message).startClean()// 清理会话.withWillQos(MqttQos.atLeastOnce);client.connectionMessage connMessage;try {await client.connect();} catch (e) {print(Exception: $e);client.disconnect();}//用于监听已订阅主题的消息到达。client.updates?.listen((ListMqttReceivedMessageMqttMessage c) {final MqttPublishMessage recMess c[0].payload as MqttPublishMessage;final String pt MqttPublishPayload.bytesToStringAsString(recMess.payload.message);// 解码包含中文字符的字符串final String decodedString utf8.decode(pt.codeUnits);LogI(Received message: $decodedString from topic: ${c[0].topic});});return client;}///订阅一个主题_subscribe(String topic) {client?.subscribe(topic, MqttQos.atLeastOnce);}///订阅多个主题topicSubscribe(ListString topics) async {this.topics.addAll(topics);if (client?.connectionStatus?.state MqttConnectionState.connected) {topics.forEach((topic) {_subscribe(topic);});} else {//未连接成功 每隔3s重新订阅Future.delayed(const Duration(seconds: 3), () {topicSubscribe(topics);});}}///取消订阅_unsubscribe() {client?.unsubscribe(topic/test);}///断开连接_disconnect() {client?.disconnect();}// 连接成功void onConnected() {print(连接成功);}// 连接断开void onDisconnected() {print(连接断开);}// 订阅主题成功void onSubscribed(String topic) {print(订阅主题成功: $topic);}// 订阅主题失败void onSubscribeFail(String topic) {print(订阅主题失败 $topic);}// 成功取消订阅void onUnsubscribed(String? topic) {print(成功取消订阅: $topic);}// 收到 PING 响应void pong() {print(收到 PING 响应 Ping response client callback invoked);}}
