1. Add dependencies:
First, you need to add the mqtt_client dependency to the pubspec.yaml file of the Flutter project.
dependencies:
#https://pub.dev/packages/mqtt_client
mqtt_client: ^10.0.02.创建MQTT客户端并连接到MQTT服务器:
2. Create an MQTT client instance to connect and communicate
Future<MqttServerClient> 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;
}
Where host is the host name, port is the port number, and cid is the client ID. You can assign a unique identifier to it as needed.
3. Subscribe to topics:
Once connected to the MQTT server, you can subscribe to topics of interest to receive messages. The following is a sample code for subscribing to a topic:
//Used to listen for the arrival of messages from a subscribed topic.
client.updates?.listen((List<MqttReceivedMessage<MqttMessage>> 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: ${
c[0].topic}');
});
Subscribe to a topic through the client.subscribe method and use the client.updates stream to listen for received messages.
4.Publish news:
Use an MQTT client to publish messages to a specific topic. The following is sample code for publishing a message:
final MqttClientPayloadBuilder builder = MqttClientPayloadBuilder();
builder.addString('Hello from Flutter');
client.publishMessage('your_topic', MqttQos.exactlyOnce, builder.payload);
In the above code, use MqttClientPayloadBuilder to build the payload of the message, and then use the client.publishMessage method to publish the message to the specified topic.
5. Disconnect:
When you no longer need to communicate with the MQTT server, remember to disconnect to free up resources:
client.disconnect();
Complete code:
class XMqttClient {
static final XMqttClient _instance = XMqttClient._();
static XMqttClient get instance => _instance;
static const host = '139.196.xx.xx';//替换成你自己的主机
static const port = 1883;//端口号
static const user = 'admin';//用户
static const pwd = 'public';//密码
List<String> topics = [];
MqttClient? client;
XMqttClient._() {
_initMqtt();
}
_initMqtt() async {
//clientld 确保唯一性，否则如果两台机器的clientld 相同 则会连上立刻断开连接！！！
String clientId = '${
DateTime.now().millisecondsSinceEpoch}asc';
client = await connect(clientId);
}
Future<MqttServerClient> 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((List<MqttReceivedMessage<MqttMessage>> 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(List<String> 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');
}
}