Question

I seem to be having trouble with updating a TextView from a thread. I have a GameConnection class (which manages a socket connection) which I want to use across activities. It calls a local “onMessage”, which then uses the target handler to call dispatch Message. The “Handler” in this case, is in my GameBrowser activity.

Here’s code from the GameConnection class.

in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
out = new PrintWriter(socket.getOutputStream(),true);

String message = "".intern();

// as a newline character is read, we interpret it as a message
while ((message = in.readLine()) != null && isConnected){
    onMessage(message);
}

As said above, a local method “onMessage” method handles dispatching of the message.

  private void onMessage(String message){
       ... // create message from String
      handler.dispatchMessage( msg );
  }

However, when I get the response in the GameBrowser class, I get a CalledFromWrongThreadException . Initially, I was using a callback method, which of course wasn’t working. So, after some research, I’ve found that I have to use a Handler, but I can’t seem to get it right.

public class GameBrowser extends Activity {

@Override
protected void onCreate(Bundle savedInstanceState) {

    super.onCreate(savedInstanceState);
    Log.d(C.tag, "GameBrowser.onCreate addr:" + this);

    handler = new Handler(new HandlerCallback());

    connection.addMessageListener(handler);
    connection.connect();
    txtGameLabel = (TextView)findViewById( R.id.txtGamesLabel);
    setContentView(R.layout.game_browser);


}

private class HandlerCallback implements Callback{

    @Override
    public boolean handleMessage(Message msg) {

        if (txtGameLabel == null){
            txtGameLabel =  (TextView)findViewById( R.id.txtGamesLabel);
        }

        String message = msg.getData().getString("message");

        Log.d(C.tag, "GameBrowser recieved message " + message);

        txtGameLabel.setText("Data: " + message);

        return true;
    }
}

}

Answer 1

I figured out what I was doing wrong. Instead of calling the handler from the socket thread, I used a callback, then used Runnable to post to the handler in the GameConnection class. When onMessage executes “run”, which executes “updateTextField”, we’re back in the main thread.

@Override
public void onMessage(final String message) {

    handler.post(new Runnable(){
        @Override
        public void run() {
            updateTextField(message);

        }
    });

}

private void updateTextField(String message){
    if (txtGameLabel == null)
        txtGameLabel = (TextView)findViewById( R.id.txtGamesLabel);

    txtGameLabel.setText(message);
}