Updating Android UI using threads

I am writing an Android Chat App. I am listening for connections and I receive data and I can see it in the Log.d, but whenever I try to update my UI the application crashes.

Code snippet:

private class chatReceiver implements Runnable {
    @Override
    public void run() {
        try {
            skt = new DatagramSocket(Integer.parseInt(Main.prefs.getString("port_number", "5432")));
            DatagramPacket rcvPkt = new DatagramPacket(r开发者_开发问答cvBuf,rcvBuf.length);
            String ack = "Hello from our SimpleUDPServer";
            byte[] sndBuf = ack.getBytes();
            while (true) {
                Log.d("Server received: " ,"entered loop");
                skt.receive(rcvPkt);
                String rcvMsg = new String(rcvBuf, 0, rcvPkt.getLength(), "UTF-8");
                Log.d("Server received: " ,"receiving" + rcvMsg);
                if (rcvMsg != null) {
                    Log.d("Server received: " ,"not equal null");
                    // I want to update my UI here
                }
                DatagramPacket k = new DatagramPacket(sndBuf, sndBuf.length,
                        rcvPkt.getAddress(), rcvPkt.getPort());
                skt.send(k);
                Log.d("Server sent" ,ack);

            }
        } catch (IOException ex) {
            Log.d("ThreadStart", "Error Starting thread" + ex.getStackTrace());
        }

    }
} 

and to update the UI I do use :

public static void updateUI(Bubble b, View itemView) {

    TextView txt_display_name = (TextView) itemView
            .findViewById(R.id.display_name);
    txt_display_name.setText(b.getDisplay_name());
    TextView txt_chat_body = (TextView) itemView
            .findViewById(R.id.chat_body);
    txt_chat_body.setText(b.getChat_body());
    TextView txt_creation_date = (TextView) itemView
            .findViewById(R.id.creation_date);
    txt_creation_date.setText(b.getCreation_time());
}

The application keeps crashing.

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You cannot change UI elements from a non-UI thread. Try using runOnUiThread.

runOnUiThread(new Runnable(){
    @Override
    public void run(){
        // change UI elements here
    }
});

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You cannot touch anything in the UI thread from a background thread, to do that use Handlers, initialize your background thread passing it a Handler object. When data arrives to use the handler to send a message to the UI. In the UI when the message from the background thread comes, just update the Views.

Example Code Snippet :

in the background thread:

if(dataArrives){
    Message msg = handler.obtainMessage();
    msg.what = UPDATE_IMAGE;
    msg.obj = bitmap;
    msg.arg1 = index;
    handler.sendMessage(msg);
}

in the UI thread:

final Handler handler = new Handler(){
  @Override
  public void handleMessage(Message msg) {
    if(msg.what==UPDATE_IMAGE){
      images.get(msg.arg1).setImageBitmap((Bitmap) msg.obj);
    }
    super.handleMessage(msg);
  }
};

and pass the handler to the background thread.

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Or just use AsyncTask, it is more useful IMHO.

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Use this method to update your UI from the worker thread, here it's explained well.

Note: - If you are using progressbar.setProgress(progress) you can update directly from the worker thread because the ProgressBar internally call setProgress() method using Handler.