android studio mqt

### 如何在 Android Studio 中设置和使用 MQTT #### 配置项目权限 为了使应用程序能够通过网络发送和接收消息，在 `AndroidManifest.xml` 文件中需声明必要的权限： ```xml <uses-permission android:name="android.permission.INTERNET" /> <uses-permission android:name="android.permission.WAKE_LOCK" /> <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />[^2] ``` 这些权限允许应用访问互联网并保持处理器处于唤醒状态。 #### 添加依赖库 要在项目里集成 MQTT 客户端功能，推荐采用 Eclipse Paho 库。打开项目的 build.gradle (Module: app)，加入如下依赖项： ```gradle dependencies { implementation 'org.eclipse.paho:org.eclipse.paho.client.mqttv3:1.2.5' } ``` 同步 Gradle 后即可引入所需类文件。 #### 编写客户端代码 下面展示了一个基本的 MQTT 连接实例化过程以及订阅主题的方法： ```java import org.eclipse.paho.client.mqttv3.IMqttDeliveryToken; import org.eclipse.paho.client.mqttv3.MqttCallback; import org.eclipse.paho.client.mqttv3.MqttClient; import org.eclipse.paho.client.mqttv3.MqttConnectOptions; import org.eclipse.paho.client.mqttv3.MqttException; import org.eclipse.paho.client.mqttv3.MqttMessage; public class MqttHelper { private static final String BROKER_URL = "tcp://broker.emqx.io:1883"; // 或者本地服务器地址 private static final String CLIENT_ID = "TestClientId"; public void connect() throws MqttException { MqttClient client = new MqttClient(BROKER_URL, CLIENT_ID); MqttConnectOptions options = new MqttConnectOptions(); options.setCleanSession(true); try { client.connect(options); System.out.println("Connected to broker"); subscribeToTopic(client, "/test/topic"); } catch (MqttException e) { throw e; } } private void subscribeToTopic(MqttClient client, String topic) throws MqttException { client.subscribe(topic); client.setCallback(new MqttCallback() { @Override public void connectionLost(Throwable cause) {} @Override public void messageArrived(String topic, MqttMessage message) throws Exception { System.out.printf("Received Message on Topic %s :%n%s%n", topic, new String(message.getPayload())); } @Override public void deliveryComplete(IMqttDeliveryToken token) {} }); } } ``` 此段代码展示了如何创建一个 MQTT 客户端对象并与指定代理建立连接；同时定义了当收到新消息时触发的消息回调函数[^1]。