问题描述:
在安卓Oreo/Pie版本上,使用Paho MQTT库无法在后台启动活动。
解决方法:
在安卓Oreo版本及以上,后台限制了活动的启动方式,需要使用前台服务(Foreground Service)来启动活动。以下是一个使用Paho MQTT库在后台启动活动的示例代码:
import android.app.Notification;
import android.app.NotificationChannel;
import android.app.NotificationManager;
import android.app.PendingIntent;
import android.app.Service;
import android.content.Context;
import android.content.Intent;
import android.os.Build;
import android.os.IBinder;
import android.support.v4.app.NotificationCompat;
import org.eclipse.paho.android.service.MqttAndroidClient;
import org.eclipse.paho.client.mqttv3.IMqttActionListener;
import org.eclipse.paho.client.mqttv3.IMqttToken;
import org.eclipse.paho.client.mqttv3.MqttCallback;
import org.eclipse.paho.client.mqttv3.MqttConnectOptions;
import org.eclipse.paho.client.mqttv3.MqttException;
import org.eclipse.paho.client.mqttv3.MqttMessage;
public class MQTTService extends Service {
private static final String CHANNEL_ID = "MQTTServiceChannel";
private MqttAndroidClient mqttClient;
@Override
public void onCreate() {
super.onCreate();
startForeground(1, createNotification());
}
@Override
public int onStartCommand(Intent intent, int flags, int startId) {
if (intent.getAction().equals("START")) {
String clientId = "your_client_id";
String serverUri = "tcp://your_mqtt_server:1883";
String topic = "your_topic";
mqttClient = new MqttAndroidClient(this, serverUri, clientId);
mqttClient.setCallback(new MqttCallback() {
@Override
public void connectionLost(Throwable cause) {
// 连接丢失时的处理
}
@Override
public void messageArrived(String topic, MqttMessage message) throws Exception {
// 消息到达时的处理
}
@Override
public void deliveryComplete(IMqttDeliveryToken token) {
// 消息发送完成后的处理
}
});
MqttConnectOptions connectOptions = new MqttConnectOptions();
connectOptions.setCleanSession(true);
try {
IMqttToken token = mqttClient.connect(connectOptions);
token.setActionCallback(new IMqttActionListener() {
@Override
public void onSuccess(IMqttToken asyncActionToken) {
// 连接成功时的处理
subscribeToTopic();
}
@Override
public void onFailure(IMqttToken asyncActionToken, Throwable exception) {
// 连接失败时的处理
}
});
} catch (MqttException e) {
e.printStackTrace();
}
} else if (intent.getAction().equals("STOP")) {
stopSelf();
}
return START_STICKY;
}
@Override
public IBinder onBind(Intent intent) {
return null;
}
private void subscribeToTopic() {
String topic = "your_topic";
int qos = 1;
try {
IMqttToken token = mqttClient.subscribe(topic, qos);
token.setActionCallback(new IMqttActionListener() {
@Override
public void onSuccess(IMqttToken asyncActionToken) {
// 订阅成功时的处理
}
@Override
public void onFailure(IMqttToken asyncActionToken, Throwable exception) {
// 订阅失败时的处理
}
});
} catch (MqttException e) {
e.printStackTrace();
}
}
private Notification createNotification() {
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
NotificationChannel channel = new NotificationChannel(CHANNEL_ID, "MQTT Service", NotificationManager.IMPORTANCE_DEFAULT);
NotificationManager notificationManager = getSystemService(NotificationManager.class);
notificationManager.createNotificationChannel(channel);
}
Intent notificationIntent = new Intent(this, MainActivity.class);
PendingIntent pendingIntent = PendingIntent.getActivity(this, 0, notificationIntent, 0);
return new NotificationCompat.Builder(this, CHANNEL_ID)
.setContentTitle("MQTT Service")
.setContentText("Running in background")
.setSmallIcon(R.drawable.ic_notification)
.setContentIntent(pendingIntent)
.build();
}
}
在你的活动或广播接收器中,使用以下代码启动和停止MQTT服务:
// 启动MQTT服务
Intent startIntent = new Intent(this, MQTTService.class);
startIntent.setAction("