Question

我正在为项目测试 MQTT 。我还能够在客户端连接时接收客户已订阅的主题的消息。我已将QoS设置为1，cleanSession设置为false。但是当我的客户端再次连接时，我无法接收发送到订阅主题的消息。在我的应用程序中，几乎所有的工作都是由帮助程序服务完成的。

这是我的代码

的AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>

<uses-permission android:name="android.permission.WAKE_LOCK" />
<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />

<application
    android:allowBackup="true"
    android:icon="@mipmap/ic_launcher"
    android:label="@string/app_name"
    android:theme="@style/AppTheme" >
    <activity
        android:name=".MainActivity"
        android:label="@string/app_name"
        android:screenOrientation="portrait" >
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />

            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>

    <service
        android:name=".MqttHelperService"
        android:enabled="true"
        android:exported="true" />

    <!-- MqttService -->
    <service android:name="org.eclipse.paho.android.service.MqttService" />
</application>

MainActivity.java

package com.prateek.mqtttest;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;

public class MainActivity extends Activity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        startService(new Intent(getBaseContext(), MqttHelperService.class));
    }
}

MqttHelperService.java

package com.prateek.mqtttest;

import android.app.Service;
import android.content.Intent;
import android.os.Binder;
import android.os.IBinder;
import android.widget.Toast;

import org.eclipse.paho.android.service.MqttAndroidClient;
import org.eclipse.paho.client.mqttv3.IMqttActionListener;
import org.eclipse.paho.client.mqttv3.IMqttDeliveryToken;
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 MqttHelperService extends Service implements MqttCallback {

    private static final String MQTT_URI = "tcp://broker.mqttdashboard.com:1883";
    private static final String CLIENT_ID = "prateek";
    private static final String MQTT_TOPIC = "mqttmessenger";
    private static final int QOS = 1;
    private MqttAndroidClient client;

    public MqttHelperService() {
    }

    @Override
    public int onStartCommand(Intent intent, int flags, int startId) {
        Toast.makeText(this, "MQTT Helper Service Started", Toast.LENGTH_SHORT).show();
        new Thread(new Runnable() {
            @Override
            public void run() {
                connect();
            }
        }, "MqttHelperService").start();
        return START_STICKY;
    }

    public class MqttHelperBinder extends Binder {
        public MqttHelperService getService(){
            return MqttHelperService.this;
        }
    }

    public void connect() {
        client = new MqttAndroidClient(this, MQTT_URI, CLIENT_ID);
        client.setCallback(this);

        try {
            MqttConnectOptions options = new MqttConnectOptions();
            options.setCleanSession(false);
            client.connect(options, new IMqttActionListener() {
                @Override
                public void onSuccess(IMqttToken iMqttToken) {
                    Toast.makeText(getBaseContext(), "connected to MQTT broker", Toast.LENGTH_SHORT).show();
                    subscribe();
                }

                @Override
                public void onFailure(IMqttToken iMqttToken, Throwable throwable) {
                    Toast.makeText(getBaseContext(), "failed to connect: " + throwable.getMessage(), Toast.LENGTH_SHORT).show();
                }
            });
        } catch (MqttException e) {
            Toast.makeText(this, "could not connect to MQTT broker at " + MQTT_URI, Toast.LENGTH_SHORT).show();
        }
    }

    public void subscribe() {
        try {
            IMqttToken token = client.subscribe(MQTT_TOPIC, QOS, null, new IMqttActionListener() {
                @Override
                public void onSuccess(IMqttToken iMqttToken) {
                    Toast.makeText(getBaseContext(), "subscription successful", Toast.LENGTH_SHORT).show();
                }

                @Override
                public void onFailure(IMqttToken iMqttToken, Throwable throwable) {
                    Toast.makeText(getBaseContext(), "subscription failed: " + throwable, Toast.LENGTH_SHORT).show();
                }
            });

        } catch (MqttException e) {
            Toast.makeText(this, "could not subscribe", Toast.LENGTH_SHORT).show();
        }
    }

    @Override
    public IBinder onBind(Intent intent) {
        // TODO: Return the communication channel to the service.
        throw new UnsupportedOperationException("Not yet implemented");
    }

    @Override
    public void connectionLost(Throwable throwable) {
        Toast.makeText(this, "connection lost", Toast.LENGTH_SHORT).show();
    }

    @Override
    public void messageArrived(String s, MqttMessage mqttMessage) throws Exception {
        Toast.makeText(this, "message received on topic " + s, Toast.LENGTH_SHORT).show();
    }

    @Override
    public void deliveryComplete(IMqttDeliveryToken iMqttDeliveryToken) {
    }

    @Override
    public void onDestroy() {
        super.onDestroy();
        Toast.makeText(this, "Service Destroyed", Toast.LENGTH_SHORT).show();
    }


}

我甚至检查了此链接With the clear session flag set to FALSE, I am missing the published values，但在我的代码中找不到错误

Answer 1

我最近遇到了同样的问题。现在我认为解决方案非常简单，但我花了很多时间来解决这个问题。

这条线很糟糕：

client.connect(mqttOptions, mqqtActionListener);

'正确'是：

client.connect(mqttOptions, null, mqqtActionListener);

如果使用2个参数调用 connect 方法，则使用此构造函数：

public IMqttToken connect(Object userContext, IMqttActionListener callback) throws MqttException

而不是正确的：

public IMqttToken connect(MqttConnectOptions options, Object userContext, IMqttActionListener callback) throws MqttException

我希望这也是你的问题。

Answer 2

最可能的问题是发布的消息是QoS = 0。订阅和发布都必须是QoS＆gt; 0才能排队等待持久客户端。

您已确认消息是使用QoS 1发布的，因此接下来要做的是使用已知的工作工具进行测试，以消除代码可能出现的问题。我试过了：

mosquitto_sub -i prateek -t mqttmessenger -h broker.mqttdashboard.com -v -d -c -q 1

并确认我可以在连接时收到消息：

mosquitto_pub -q 1 -t mqttmessenger -m hello2 -h broker.mqttdashboard.com

然后我断开了mosquitto_sub客户端，并使用相同的mosquitto_pub命令发布了另一条消息。使用相同的命令重新连接mosquitto_sub不会产生任何消息，正如您所看到的那样。重复该过程但使用test.mosquitto.org作为代理，行为符合预期。看起来broker.mqttdashboard.com未配置为允许持久客户端。

Paho MQTT cleanSession设置为false但未接收消息

2 个答案: