Why onDestroy doesn't kill its methods?

Issue

I am working on xmpp chat on Android now. I have next situation: 1) I have singletone class with XMPPConnection and 2 activities. 2) 1st activity is just a list of contacts, which I can choose and start message with. 3) In second activity(chat) I setup listeners for my connection and add some signal, which plays, when message from particular contact is received. 4) Then I close chat activity and onDestroy method is called. 5) And then, if I message to my app - I hear the signal, which plays in destroyed activity(I mean method which plays signal must be destroyed with chat activity).

Please, explain me why it's possible.

    public class ChatActivity extends ActionBarActivity {
    ...
    public void beep() {
            Uri notification = RingtoneManager
                    .getDefaultUri(RingtoneManager.TYPE_NOTIFICATION);
            RingtoneManager.getRingtone(getApplicationContext(), notification).play();
        }
    ...

    public void setupListeners(XMPPConnection connection) {
            if(connection != null) {
                //Set a listener for chat messages
                connection.addPacketListener(new PacketListener() {
                    @Override
                    public void processPacket(Packet packet) {
                        Message message = (Message) packet;
                        if (message.getBody() != null && message.getFrom()
                                .contains(chatModel.getRecipient())) {
                            chatModel.addMessage(StringUtils.parseBareAddress(message.getFrom())
                                    + " :" + message.getBody());
                            beep();
                        }
                    }
                }, new MessageTypeFilter(Message.Type.chat));

                //Set a listener for normal messages
                connection.addPacketListener(new PacketListener() {
                    @Override
                    public void processPacket(Packet packet) {
                        Message message = (Message) packet;
                        if(message.getBody() != null && message.getFrom()
                                .contains(chatModel.getRecipient())) {
                            chatModel.addMessage(StringUtils.parseBareAddress(message.getFrom())
                                    + " :" + message.getBody());
                            beep();
                        }
                    }
                }, new MessageTypeFilter(Message.Type.normal));
       }
   }

Solution

Have you tried disconnecting the Connection in the onDestroy of your Activity? Or to remove the listeners? Because of these inner classes, which hold a (hidden) reference to their outer class - your Activity in this case, the Activity possibly can't be garbage collected. So removing the listeners or disconnecting the Connection should do the trick.

Edit: Like Gusdor said, you'd want to remove the listeners in the onPause() Method and add them again in the onResume().

Edit2: If you want that the XMPP Connection runs in the background, you should consider using a background Service for handling the Connection and the messages, instead of the Activity.

Answered By - tknell