mjn mjn - 4 months ago 41
Android Question

Paho Android client drops connection when a message is shown

I am trying to use the basic Eclipse Paho MQTT client version 1.1.0 to connect to a CloudAMQP RabbitMQ instance, subscribe to a topic, and receive messages (which I send from the web admin console).

It works well if the application sends all message payloads to the Log output.

If the application adds the message to a TextView, the message appears, but the connection is dropped immediately and no more message are received.

The full project is available at GitHub. A simple example is below.

There is a service-based MQTT Paho client, but I thought that for very simple applications the basic client should be able to receive and show messages in the Android app UI.

...

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.MqttClientPersistence;
import org.eclipse.paho.client.mqttv3.MqttConnectOptions;
import org.eclipse.paho.client.mqttv3.MqttException;
import org.eclipse.paho.client.mqttv3.MqttMessage;
import org.eclipse.paho.client.mqttv3.persist.MemoryPersistence;

public class MainActivity extends AppCompatActivity implements MqttCallback {

private static final String TAG = "main";
private Connection connection;

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);

configureUI();
}

private Button buttonConnect;
private TextView messageWindow;


private void configureUI() {
buttonConnect = (Button) findViewById(R.id.buttonConnect);
messageWindow = (TextView) findViewById(R.id.messageWindow);

buttonConnect.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
String s = "***";
String d = "test";
String u = "***";
String p = "***";

if (connection != null && connection.isConnected()) {
connection.disconnect();
connection = null;
messageWindow.setText(String.format("Disconnected from server %s",
new Object[]{s}));
return;
}

messageWindow.setText(String.format("Connecting to server %s as user %s",
new Object[]{s, u}));

connection = new Connection(MainActivity.this, MainActivity.this, s, u, p);
connection.connect();

if (connection.isConnected()) {
messageWindow.append("\n\n");
messageWindow.append(String.format("Connected, listening for messages from topic %s",
new Object[]{d}));
connection.subscribe(d);
}
}
});
}

@Override
public void connectionLost(Throwable cause) {
Log.e(TAG, "connectionLost" + cause.getMessage());
}

@Override
public void messageArrived(String topic, MqttMessage message) throws Exception {
String msg = new String(message.getPayload());
Log.i(TAG, "Message Arrived: " + msg);
// messageWindow.append(msg);
}

@Override
public void deliveryComplete(IMqttDeliveryToken token) {
Log.i(TAG, "Delivery Complete!");
}

class Connection {
private static final String TAG = "conn";
private static final String protocol = "tcp://";
private static final int port = 1883;
private static final int version = MqttConnectOptions.MQTT_VERSION_3_1_1;
private static final int keepAliveSeconds = 20 * 60;

private final Context context;
private MqttClient client;

private final String server;
private final String user;
private final String pass;

private final MqttConnectOptions options = new MqttConnectOptions();

public Connection(Context ctx, MqttCallback mqttCallback, String server, String user, String pass) {
this.context = ctx;
this.server = server;
this.user = user;
this.pass = pass;

MqttClientPersistence memPer = new MemoryPersistence();
try {
String url = protocol + server + ":" + port;
client = new MqttClient(url, MqttClient.generateClientId(), memPer);
client.setCallback(mqttCallback);
} catch (MqttException e) {
e.printStackTrace();
}

options.setUserName(user + ":" + user);
options.setPassword(pass.toCharArray());
options.setMqttVersion(version);
options.setKeepAliveInterval(keepAliveSeconds);
}

void connect() {
Log.i(TAG, "buttonConnect");
try {
client.connect(options);
} catch (MqttException ex) {
Log.e(TAG, "Connection attempt failed with reason code = " + ex.getReasonCode() + ":" + ex.getCause());
}
}

public boolean isConnected() {
return client.isConnected();
}

public void disconnect() {
try {
client.disconnect();
} catch (MqttException e) {
Log.e(TAG, "Disconnect failed with reason code = " + e.getReasonCode());
}
}

void subscribe(String dest) {
try {
client.subscribe(dest);
} catch (MqttException e) {
Log.e(TAG, "Subscribe failed with reason code = " + e.getReasonCode());
}
}
}
}

Answer

I would guess this is because you are trying to update the TextView from a none UI thread.

Try wrapping the messageWindow.append(msg); in a runOnUiThread call.

public void messageArrived(String topic, MqttMessage message) throws Exception {
    String msg = new String(message.getPayload());
    Log.i(TAG, "Message Arrived: " + msg);
    runOnUiThread(new Runnable(){
       public void run() {
           messageWindow.append(msg);
       }
    });
}