error: Only the original thread that created a view hierarchy can touch its views-Collection of common programming errors

Hi and thank you for looking at my question. I am an intermediate programmer in C but an Android newbie. I have been trying to get a chat programming working. Assuming everything else in the code below works perfectly. The one question I like to ask is when I try to setText() from a thread running, I get an exception above. I looked at many many websites and here too. Found many things, but I really do not understand. Please explain to me in the most simple way or offer me some simple fix if possible.

Thank you very much!!

public class chatter extends Activity {

private String name = "Unknown User";

/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);



    final EditText msgToServer = (EditText) findViewById(R.id.msgBox);
    final EditText chatFromServer = (EditText) findViewById(R.id.chatBox); 

    final Button MsgToServer = (Button) findViewById(R.id.sendButton);

    Socket socket = null;
    String ipAddress = "192.168.1.103";
    try {
        InetAddress serverAddr = InetAddress.getByName(ipAddress);
        Socket socketMain = new Socket(serverAddr, 4444);
        socket = socketMain;
    } catch (IOException e) {
        // TODO Auto-generated catch block
        Log.e("TCP", "error", e);
    }

    final OutMsg outMsg = new OutMsg(socket);
    Thread msgSenderThread = new Thread(outMsg);
    msgSenderThread.start();

    //chatFromServer.post(new InMsg(socket, chatFromServer));
    Thread msgReceiverThread = new Thread(new InMsg(socket, chatFromServer));
    msgReceiverThread.start();

    MsgToServer.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            String msgToServerString; 
            msgToServerString = msgToServer.getText().toString();
            outMsg.message = name + ": " + msgToServerString;
            outMsg.readyToSend = true;
            msgToServer.setText("");
        }
    });
}

public void updateResultsInUi (String msg)
{
    final EditText chatFromServer = (EditText) findViewById(R.id.chatBox); 
    chatFromServer.setText(msg); 
}

public class InMsg implements Runnable {

    Socket socket;
    EditText chatFromServer;
    public InMsg(Socket socket, EditText chatFromServer)
    {
        this.socket = socket;
        this.chatFromServer = chatFromServer;
    }

    public void run(){
        try {
        BufferedReader in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
        String str = "FIRSTMESSAGEFROMSERVER";
            while (true)
            {
                if (str.equals("FIRSTMESSAGEFROMSERVER"))
                    str = in.readLine();
                else
                    str = str + "\n" + in.readLine();
                Log.e("TCP", "got the message: " + str);
     //Here is where went wrong******************
                chatFromServer.setText(str);
     //******************************************
            }
        } catch (IOException e) {
            // TODO Auto-generated catch block
            Log.e("TCP", "error in receiving", e);
        }
    }

}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    MenuInflater inflater = getMenuInflater();
    inflater.inflate(R.menu.menu, menu);
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle item selection
    switch (item.getItemId()) {
    case R.id.setNameMenu:
        setname();
        return true;
    default:
        return super.onOptionsItemSelected(item);
    }
}

public void populateChatBox (String msgFromS)
{
    Log.e("TCP", "going in to popC");
    final EditText textNameInput = (EditText) findViewById(R.id.nameBox);
    Log.e("TCP", " popC");
    textNameInput.setText(msgFromS);
    Log.e("TCP", "going out from popC");
}

public void setname()
{
    setContentView(R.layout.custom_dialog);
    final EditText textNameInput = (EditText) findViewById(R.id.nameBox);
    Button submitNameButton = (Button) findViewById(R.id.submitNameButton);
    submitNameButton.setOnClickListener(new OnClickListener() {
    @Override
        public void onClick(View v) {
        String nameinput = textNameInput.getText().toString();
            if (!name.equals(""))
                name = nameinput;
            setContentView(R.layout.main);
        }
    });
}
}

1. In your run() method:

   Message msg = new Message();
   String textTochange = "text";
   msg.obj = textTochange;
   mHandler.sendMessage(msg);
   

   Create the mHandler in your UI thread;

   Handler mHandler = new Handler() {
           @Override
           public void handleMessage(Message msg) {
               String text = (String)msg.obj;
               //call setText here
           }
   };
   

2. You are not on the UI thread when setting the text. You need to be on UI if you want to work on UI items. Create a message handler on the UI thread, post your messages to it and call setText from the handler on the UI thread.

3. you can do this whenever you are in a thread:

   msgToServer.post(new Runnable() {
       public void run() {
           msgToServer.setText("your text here");
       }
   }
   

4. Your problem is that there are certain interactions that you can only do on the UI thread. This is one of them.

   Looks like you might want to use AsyncTask

   http://developer.android.com/reference/android/os/AsyncTask.html

   Basically you could make your Runnable an AsyncTask instead and do the setText in onProgressUpdate, which gets run on the UIThread.

Originally posted 2013-11-09 21:08:44.