AndroidAsync - updating views from WebSocket.StringCallback()

Question

i'm writinig some small chat app, and i'm using AndroidAsync to get WebSocket client functionality in my application. So, the trouble is whenever i try to modify my listView from WebSocket.StringCallback().onStringAvailable(String) it causes an exception:

android.view.ViewRoot$CalledFromWrongThreadException: Only the original thread that created a view hierarchy can touch its views.
            at android.view.ViewRoot.checkThread(ViewRoot.java:2932)
            at android.view.ViewRoot.focusableViewAvailable(ViewRoot.java:1712)
            at android.view.ViewGroup.focusableViewAvailable(ViewGroup.java:452)
            at android.view.ViewGroup.focusableViewAvailable(ViewGroup.java:452)
            at android.view.ViewGroup.focusableViewAvailable(ViewGroup.java:452)
            at android.view.ViewGroup.focusableViewAvailable(ViewGroup.java:452)
            at android.view.ViewGroup.focusableViewAvailable(ViewGroup.java:452)
            at android.view.View.setFlags(View.java:4614)
            at android.view.View.setFocusableInTouchMode(View.java:3190)
            at android.widget.AdapterView.checkFocus(AdapterView.java:694)
            at android.widget.AdapterView$AdapterDataSetObserver.onChanged(AdapterView.java:789)
            at android.database.DataSetObservable.notifyChanged(DataSetObservable.java:31)
            at android.widget.BaseAdapter.notifyDataSetChanged(BaseAdapter.java:50)
            at android.widget.ArrayAdapter.notifyDataSetChanged(ArrayAdapter.java:247)
            at persilabtest.zulfigarov.com.chatapp.ChatActivity$1$1.onStringAvailable(ChatActivity.java:76)
            at com.koushikdutta.async.http.WebSocketImpl$1.onMessage(WebSocketImpl.java:88)
            at com.koushikdutta.async.http.HybiParser.emitFrame(HybiParser.java:420)
            at com.koushikdutta.async.http.HybiParser.access$800(HybiParser.java:46)
            at com.koushikdutta.async.http.HybiParser$5.onDataAvailable(HybiParser.java:197)
            at com.koushikdutta.async.DataEmitterReader.handlePendingData(DataEmitterReader.java:24)
            at com.koushikdutta.async.DataEmitterReader.onDataAvailable(DataEmitterReader.java:41)
            at com.koushikdutta.async.Util.emitAllData(Util.java:22)
            at com.koushikdutta.async.AsyncNetworkSocket.onReadable(AsyncNetworkSocket.java:146)
            at com.koushikdutta.async.AsyncServer.runLoop(AsyncServer.java:788)
            at com.koushikdutta.async.AsyncServer.run(AsyncServer.java:626)
            at com.koushikdutta.async.AsyncServer.access$700(AsyncServer.java:41)
            at com.koushikdutta.async.AsyncServer$13.run(AsyncServer.java:568) 

I've already understood that I can't modify a view from non-UI threads. But i don't know how else i can update them in this situation. Here's my ChatActivity code:

public class ChatActivity extends ActionBarActivity
{
    private static final String WS_ADDRESS = "ws://192.168.0.106:8084/TestChatServer/chat";

    @InjectView(R.id.btnSend)
    Button btnSend;

    @InjectView(R.id.lvChat)
    ListView lvChat;

    @InjectView(R.id.etMsg)
    EditText etMsg;

    List<String> mMessages = new ArrayList<String>();

    ArrayAdapter<String> adapter;

    @Override
    protected void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_chat);
        ButterKnife.inject(this);
        adapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, mMessages);
        lvChat.setAdapter(adapter);

        AsyncHttpClient.getDefaultInstance()
                .websocket(WS_ADDRESS, null, new AsyncHttpClient.WebSocketConnectCallback()
                {
                    @Override
                    public void onCompleted(Exception ex, WebSocket webSocket)
                    {

                        if (ex != null)
                        {
                            ex.printStackTrace();
                            return;
                        }
                        Log.d("myLogs", "OK");

                        webSocket.setStringCallback(new WebSocket.StringCallback()
                        {
                            @Override
                            public void onStringAvailable(String s)
                            {
                                String newStr = s.replaceAll("(#+\\S+)", "<font color='#EE0000'>$1</font>");
                                Log.d("myLogs", s + "\n" + newStr);
                                mMessages.add(newStr);
                                //This line causes the exception
                                adapter.notifyDataSetChanged();
                            }
                        });
                    }
                });

    }
} 

So, any ideas how can i get my listView updated every time the new message is delivered?

Answer 1

You will want to make sure that you are updating the views from the UI thread. You can do this by using the Activity.runOnUiThread() like this:

runOnUiThread(new Runnable() {
     @Override
     public void run() {

     //run your code that needs to update the UI here

    }
});

The reason for this error Only the original thread that created a view hierarchy can touch its views is because it detected that another thread (besides the thread that created the views) is trying to touch the views. It would cause threading issues if more than one resource was trying to make changes to something at the same time.

Answer 2

Do not run adapter.notifyDataSetChanged(); from no main thread, use instead:

new Handler().post(new Runnable() {
    @Override
    public void run() {
        adapter.notifyDataSetChanged()
    }
});