MQTT 消息在取消订阅后仍然存在，并在再次订阅时收到答案

【问题标题】：MQTT messages persists after unsubscription and is recieved on subscribing againMQTT 消息在取消订阅后仍然存在，并在再次订阅时收到
【发布时间】：2016-03-18 09:28:17
【问题描述】：

我的应用使用 android 上的 paho mqtt 库来订阅主题列表。在登录到应用程序时进行订阅，在注销时取消订阅主题。订阅时 QoS 设置为 1。

当我下次登录时，我会在我退订后收到代理发布的所有 mqtt 消息。

取消订阅的回调告诉取消订阅成功。据我所知，一旦我取消订阅，我就不应该收到任何消息。

这是我的 doConnect() 用于建立连接和订阅

   private void doConnect() {
            Log.d(TAG, "doConnect()");
            IMqttToken token;
            MqttConnectOptions options = new MqttConnectOptions();
            options.setCleanSession(false);
            options.setKeepAliveInterval(30);
            try {
            mqttClient = new MqttAsyncClient(tcp_server_URL, deviceId, new MemoryPersistence());

            token = mqttClient.connect(options);
            token.waitForCompletion(3500);
            mqttClient.setCallback(new MqttEventCallback());
            //changed single subscription of each topic to mass subscription
            // using String [] of Topics and int [] of QoS

            if (channelList != null) {
            channelListStringArray= new String[channelList.size()];
            channelListQosStringArray= new int[channelList.size()];
            for (int i = 0; i < channelList.size(); i++) {
            // creating String Array of topics and int Array of QoS
            channelListStringArray [i] = "account/" + channelList.get(i);
            channelListQosStringArray [i] = 1;
            }
            //subscribe all channels by passing all topics as String Array and QoS int array
            token = mqttClient.subscribe(channelListStringArray, channelListQosStringArray);
            token.waitForCompletion(3500);
            }

            } catch (MqttSecurityException e) {
            e.printStackTrace();
            } catch (MqttException e) {
            switch (e.getReasonCode()) {
            case MqttException.REASON_CODE_BROKER_UNAVAILABLE:
            case MqttException.REASON_CODE_CLIENT_TIMEOUT:
            case MqttException.REASON_CODE_CONNECTION_LOST:
            case MqttException.REASON_CODE_SERVER_CONNECT_ERROR:
            Log.v(TAG, "c" + e.getMessage());
            e.printStackTrace();
            break;
            case MqttException.REASON_CODE_FAILED_AUTHENTICATION:
            Intent i = new Intent("RAISEALLARM");
            i.putExtra("ALLARM", e);
            Log.e(TAG, "b" + e.getMessage());
            break;
            default:
            Log.e(TAG, "a" + e.getMessage());
            }
            }
            }

这是我取消订阅和断开连接的 onDestroy

    public void onDestroy() {
            super.onDestroy();
            //disconnect from mqtt server
            IMqttToken token;
            try {
            if (channelList != null) {
            channelListStringArray = new String[channelList.size()];
            for (int i = 0; i < channelList.size(); i++) {
            //creating array of topics
            channelListStringArray[i] = "account/" + channelList.get(i);
            }
            //unsubscribe MQTTClient by passing String array of Topics, NULL, mqttActionListener to get CallBack
            //on success or failure of unsubscription
            token = mqttClient.unsubscribe(channelListStringArray, getApplicationContext(), mqttActionListener);
            token.waitForCompletion(3500);
            }
            //Disconnect MqttCient
            token = mqttClient.disconnect();
            token.waitForCompletion(3500);
            } catch (MqttException e) {
            e.printStackTrace();
            }
            unregisterReceiver(broadcastReceiver);
            }

是因为应用退订不正确造成的吗？

【问题讨论】：

标签： android mqtt paho

【解决方案1】：

这是因为您已将 cleanSession 标志设置为 false。

如果您不希望消息排队，请将其设置为 true。

...
MqttConnectOptions options = new MqttConnectOptions();
options.setCleanSession(true);
options.setKeepAliveInterval(30);
...

Clean Session 标志告诉代理存储 QOS 1/2 订阅的所有消息，直到客户端重新连接。

【讨论】：