Question

我正在尝试为Android构建一个MQTT“监听器”应用程序，并使用this sample application作为模型。但是，原始示例会抛出“主要活动上的网络”运行时错误，因此我被迫使用AsyncTask类。

主App作为服务运行：LWMQService.java [此处代码的相关部分]

package org.iothub.lightwatchmq;

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.MqttException;
import org.eclipse.paho.client.mqttv3.MqttMessage;
import org.eclipse.paho.client.mqttv3.MqttPersistenceException;
import org.eclipse.paho.client.mqttv3.MqttTopic;
import org.eclipse.paho.client.mqttv3.persist.MemoryPersistence;

import org.iothub.lightwatchmq.PushCallback;

import android.app.Service;
import android.content.Context;
import android.content.Intent;
import android.hardware.Sensor;
import android.hardware.SensorEvent;
import android.hardware.SensorEventListener;
import android.hardware.SensorManager;
import android.os.AsyncTask;
import android.os.IBinder;
import android.util.Log;
import android.widget.Toast;
import android.provider.Settings.Secure;

public class LWMQService extends Service implements SensorEventListener {

    -----

    String BROKER_URL = "tcp://test.mosquitto.org:1883";
    String TOPIC = "iothub";
    String TOPIC2 = "iothub2";
    String ClientID ;

    private MqttClient client;

   @Override
   public IBinder onBind(Intent arg0) {
      return null;
   }

   @Override
   public int onStartCommand(Intent intent, int flags, int startId) {

      ------

       ClientID = Secure.getString(getContentResolver(), Secure.ANDROID_ID); 

       try {

           client = new MqttClient(BROKER_URL, ClientID, new MemoryPersistence());
       } catch (MqttException e) {
           e.printStackTrace();
           System.exit(1);
       }
       new mConnect ().execute();
     //  new mTransmit ().execute();
       new mListen().execute();;

      Toast.makeText(this, "Service started", Toast.LENGTH_LONG).show();
      Log.d(LogMsgID, "LightWatch Service started");
      return START_STICKY;
   }

   @Override
   public void onDestroy() {
      -----
      return;
   }

   private class mConnect extends AsyncTask<Void, Void, Void> {
         protected Void doInBackground(Void...dummy) {
             try {

                 client.connect();

             } catch (MqttException e) {
                 e.printStackTrace();
                 Log.d(LogMsgID, "Connect Failed");
                 System.exit(1);
             }
            return null;
         }
    }

   public class mListen extends AsyncTask<Void, Void, Void> {
         protected Void doInBackground(Void...dummy) {
             try {
                 client.setCallback(new PushCallback(this));
                 client.subscribe(TOPIC2);

             } catch (MqttException e) {
                 e.printStackTrace();
                 Log.d(LogMsgID, "Listen Failed");
                 System.exit(1);
             }
            return null;
         }
    }


   private class mTransmit extends AsyncTask<Void, Void, Void> {
         protected Void doInBackground(Void...dummy) {

            --------
         }

     }

   @Override
      public final void onAccuracyChanged(Sensor sensor, int accuracy) {
        // Do something here if sensor accuracy changes.
      }

    @Override
      public final void onSensorChanged(SensorEvent event) {
        // The light sensor returns a single value.
        ---
      }
}

mConnect和mTransmit（发布）类正确编译并正常工作但是mListen（subscribe）类我得到一个编译错误，指出“构造函数PushCallback（LWMQService.mListen）未定义”显示在下一行中类

client.setCallback(new PushCallback(this));

PushCallback类在另一个文件中可用：PushCallback.java

package org.iothub.lightwatchmq;

import android.app.Notification;
import android.app.NotificationManager;
import android.app.PendingIntent;
import android.content.Context;
import android.content.ContextWrapper;
import android.content.Intent;
import android.util.Log;

import org.eclipse.paho.client.mqttv3.IMqttDeliveryToken;
import org.eclipse.paho.client.mqttv3.MqttCallback;
import org.eclipse.paho.client.mqttv3.MqttDeliveryToken;
import org.eclipse.paho.client.mqttv3.MqttMessage;
import org.eclipse.paho.client.mqttv3.MqttTopic;
import org.iothub.lightwatchmq.LWMQService.mListen;

public class PushCallback implements MqttCallback {

    String LogMsgID = "iothub: ";
    private ContextWrapper context;

    public PushCallback(ContextWrapper context) {

        this.context = context;
        Log.d(LogMsgID, "PCB-1");
    }

    @Override
    public void connectionLost(Throwable cause) {
        //We should reconnect here
    }

    @Override
    public void deliveryComplete(IMqttDeliveryToken arg0) {
        // TODO Auto-generated method stub
    }

    @Override
    public void messageArrived(String Topic, MqttMessage message) throws Exception {
        // TODO Auto-generated method stub

        final Intent intent = new Intent(context, MainActivity.class);
        final PendingIntent activity = PendingIntent.getActivity(context, 0, intent, 0);
        String RecdMessage = new String(message.getPayload());
        Log.d(LogMsgID, RecdMessage);

    }
}

我承认我不是很擅长Java而且可能会犯一些明显的错误，但如果有人能帮我解决这个错误，我将不胜感激。

Answer 1

在您调用client.setCallback(new PushCallback(this)); 的范围内，此是 AsyncTask ，因为 AsyncTask 类不会扩展 ContextWrapper 它与构造函数不匹配。

将行更改为

client.setCallback(new PushCallback(LWMQService.this));

获取正确的上下文对象

Android的MQTT java应用程序中的setCallback抛出错误

1 个答案: