Question

I’m developing a chat application in Android and have run into a massive problem. I need a thread to constantly run in the background (polling a server), and have attached it to my main process via a Handle.

The main problem is: As long as this background thread is running, the foreground one grinds to a complete halt!

Here is an incomplete chunk of code (because the full version is much longer/uglier)…

public class ChatActivity extends Activity {
    ...

    private Thread chatUpdateTask;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_chat);

        ...

        chatUpdateTask = new ChatUpdateTask(handler);
        chatUpdateTask.start();
    }

    public void updateChat(JSONObject json) {
        // ...
        // Updates the chat display
    }


    // Define the Handler that receives messages from the thread and update the progress
    final Handler handler = new Handler() {
        public void handleMessage(Message msg) {
            // Get json from the sent Message and display it
            updateChat(json);
        }
    };

    public class ChatUpdateTask extends Thread {
        Handler mHandler;   // for handling things outside of the thread.

        public ChatUpdateTask(Handler h) {
            mHandler = h;               // When creating, make sure we request one!
        }//myTask

        @Override
        public void start() {
            while(mState==STATE_RUNNING) {

                // ...
                // Send message to handler here

                Thread.sleep(500);  // pause on completion

            }//wend
        }//end start

        /* sets the current state for the thread,
         * used to stop the thread */
        public void setState(int state) {
            mState = state;
        }//end setState


        public JSONObject getChatMessages() {
            // ... call server, return messages (could take up to 50 seconds to execute; 
            // server only returns messages when there are new ones
            return json;
        }
    }//end class myTask


}

Answer 1

You’re overriding start(). Threads run in their run() method.

http://docs.oracle.com/javase/tutorial/essential/concurrency/runthread.html