为什么 MQTT 服务阻塞 activity？

Question

我的应用程序来自 MainActivity onCreate()，启动连接到服务器并订阅主题的服务。此外，当我添加新连接时，我的服务会重新启动（使用 stop/startService）。我将连接数据（ip、端口等）存储在 SQL 数据库中，并在它启动后将其集中在服务中。问题是（我认为）当其中一个连接参数不正确时，服务正在等待超时并阻止 activity... 如果我设置 token.waitForCompletion(500); 它会快得多，但我猜不出那个值...

有什么办法可以解决我的问题吗？

@Override
public void onCreate() {

    Datapool();
    IntentFilter intentf = new IntentFilter();
    intentf.addAction(ConnectivityManager.CONNECTIVITY_ACTION);
    registerReceiver(mqttBroadcastReceiver, new IntentFilter(ConnectivityManager.CONNECTIVITY_ACTION));
    mConnMan = (ConnectivityManager) getSystemService(CONNECTIVITY_SERVICE);
    deviceId = String.format(DEVICE_ID_FORMAT, Settings.Secure.getString(getContentResolver(), Settings.Secure.ANDROID_ID));

}

MQTTBroadcastReceiver mqttBroadcastReceiver = new MQTTBroadcastReceiver();

class MQTTBroadcastReceiver extends BroadcastReceiver {
    @Override
    public void onReceive(Context context, Intent intent) {
        Connect();
    }

};

IMqttToken token;
int i = 0;
private HashMap<String, Boolean> _hashMap = new HashMap<>();
private void Connect(){
    for (ServiceDataModel connectionData : dataModels) {

        Log.d(TAG, "doConnect() " + connectionData.getCONNECTION_NAME());
        _hashMap.put(connectionData.getCONNECTION_NAME(), false);
        MqttConnectOptions options = new MqttConnectOptions();
        options.setCleanSession(true);
        i++;
        try {
            mqttClient = new MqttAsyncClient("tcp://" + connectionData.getSERVER_IP() + ":" + connectionData.getSERVER_PORT(), deviceId + i , new MemoryPersistence());
            token = mqttClient.connect();
            token.waitForCompletion(2500);
            if (mqttClient.isConnected()) {
                    mqttClient.setCallback(new MqttEventCallback());
                    token = mqttClient.subscribe(connectionData.getTOPIC(), Integer.parseInt(connectionData.getQOS()));
                    token.waitForCompletion(2500);
                   _hashMap.put(connectionData.getCONNECTION_NAME(), true);
            }
        }catch (Exception ex){
            Log.d(TAG, ex.toString() + connectionData.toString());
        }
    }
    sendMessageToActivity(_hashMap);
}

Answer 1

通过调用 token.waitForCompletion(2500)，您尝试先同步连接，然后同步订阅 - 这会阻塞主线程。

不要应用这些 hack，而是使用异步连接回调（下面的 mCallback 和 mConnectionCallback）。连接成功后，使用异步订阅回调（下图mSubscribeCallback）：

private final MqttCallbackExtended mCallback = new MqttCallbackExtended() {
    @Override
    public void connectComplete(boolean reconnect, String brokerAddress) {
            mqttClient.subscribe(connectionData.getTOPIC(), Integer.parseInt(connectionData.getQOS()), null, mSubscribeCallback);
    }

    @Override
    public void connectionLost(Throwable ex) {
    }

    @Override
    public void deliveryComplete(IMqttDeliveryToken deliveryToken) {
    }

    @Override
    public void messageArrived(String topic, MqttMessage mqttMessage) throws Exception {
    }
};

private final IMqttActionListener mConnectionCallback = new IMqttActionListener() {
    @Override
    public void onSuccess(IMqttToken asyncActionToken) {
        // do nothing, this case is handled in mCallback.connectComplete()
    }

    @Override
    public void onFailure(IMqttToken asyncActionToken, Throwable exception) {
    }
};

private final IMqttActionListener mSubscribeCallback = new IMqttActionListener() {
    @Override
    public void onSuccess(IMqttToken subscribeToken) {
           _hashMap.put(connectionData.getCONNECTION_NAME(), true);
    }

    @Override
    public void onFailure(IMqttToken subscribeToken, Throwable ex) {
    }

};

try {
    MqttConnectOptions connectOptions = new MqttConnectOptions();
    connectOptions.setCleanSession(true);
    connectOptions.setAutomaticReconnect(false);
    connectOptions.setUserName("username");
    connectOptions.setPassword("password".toCharArray());

    mqttClient = new MqttAsyncClient("tcp://" + connectionData.getSERVER_IP() + ":" + connectionData.getSERVER_PORT(), deviceId + i , new MemoryPersistence());
    mqttClient.setCallback(mCallback);
    mqttClient.connect(connectOptions, null, mConnectionCallback);

} catch (Exception ex) {
    Log.d(TAG, ex.toString() + connectionData.toString());
}

所以稍微重新安排一下您的应用程序，它就不会阻塞。

还考虑使用 LocalBroadcastManager 在 SQLite、MQTT 和 Activity 之间进行通信。

更新： 使用 LiveData 和 Room 而不是 LocalBroadcastManager

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