Android http соединение с OkHttp не работает

Я пытаюсь использовать OkHttp, но это постоянно. Может кто-то быстро взглянуть и посмотреть, знаете ли вы, что происходит. Спасибо.

Log cat:

01-24 08:34:46.952: E/AndroidRuntime(31953): FATAL EXCEPTION: OkHttp Dispatcher
01-24 08:34:46.952: E/AndroidRuntime(31953): java.lang.NoClassDefFoundError: okio.Okio
01-24 08:34:46.952: E/AndroidRuntime(31953):    at com.squareup.okhttp.internal.http.HttpConnection.<init>(HttpConnection.java:87)
01-24 08:34:46.952: E/AndroidRuntime(31953):    at com.squareup.okhttp.Connection.upgradeToTls(Connection.java:272)
01-24 08:34:46.952: E/AndroidRuntime(31953):    at com.squareup.okhttp.Connection.connect(Connection.java:158)
01-24 08:34:46.952: E/AndroidRuntime(31953):    at com.squareup.okhttp.Connection.connectAndSetOwner(Connection.java:174)
01-24 08:34:46.952: E/AndroidRuntime(31953):    at com.squareup.okhttp.OkHttpClient.connectAndSetOwner(OkHttpClient.java:120)
01-24 08:34:46.952: E/AndroidRuntime(31953):    at com.squareup.okhttp.internal.http.RouteSelector.next(RouteSelector.java:131)
01-24 08:34:46.952: E/AndroidRuntime(31953):    at com.squareup.okhttp.internal.http.HttpEngine.connect(HttpEngine.java:312)
01-24 08:34:46.952: E/AndroidRuntime(31953):    at com.squareup.okhttp.internal.http.HttpEngine.sendRequest(HttpEngine.java:235)
01-24 08:34:46.952: E/AndroidRuntime(31953):    at com.squareup.okhttp.Call.getResponse(Call.java:262)
01-24 08:34:46.952: E/AndroidRuntime(31953):    at com.squareup.okhttp.Call$ApplicationInterceptorChain.proceed(Call.java:219)
01-24 08:34:46.952: E/AndroidRuntime(31953):    at com.squareup.okhttp.Call.getResponseWithInterceptorChain(Call.java:192)
01-24 08:34:46.952: E/AndroidRuntime(31953):    at com.squareup.okhttp.Call.access0(Call.java:34)
01-24 08:34:46.952: E/AndroidRuntime(31953):    at com.squareup.okhttp.Call$AsyncCall.execute(Call.java:156)
01-24 08:34:46.952: E/AndroidRuntime(31953):    at com.squareup.okhttp.internal.NamedRunnable.run(NamedRunnable.java:33)
01-24 08:34:46.952: E/AndroidRuntime(31953):    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1080)
01-24 08:34:46.952: E/AndroidRuntime(31953):    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:573)
01-24 08:34:46.952: E/AndroidRuntime(31953):    at java.lang.Thread.run(Thread.java:841)

вот пример кода, который я пытаюсь использовать. Его из учебника онлайн (teamtreehouse.com) Java-код:

OkHttpClient client = new OkHttpClient();
            Request request = new Request.Builder()
                    .url(forecastUrl)
                    .build();

            Call call = client.newCall(request);
            call.enqueue(new Callback() {
                @Override
                public void onFailure(Request request, IOException e) {
                    runOnUiThread(new Runnable() {
                        @Override
                        public void run() {
                            toggleRefresh();
                        }
                    });
                    alertUserAboutError();
                }

                @Override
                public void onResponse(Response response) throws IOException {
                    runOnUiThread(new Runnable() {
                        @Override
                        public void run() {
                            toggleRefresh();
                        }
                    });

                    try {
                        String jsonData = response.body().string();
                        Log.v(TAG, jsonData);
                        if (response.isSuccessful()) {
                            mCurrentWeather = getCurrentDetails(jsonData);
                            runOnUiThread(new Runnable() {
                                @Override
                                public void run() {
                                    updateDisplay();
                                }
                            });
                        } else {
                            alertUserAboutError();
                        }
                    }
                    catch (IOException e) {
                        Log.e(TAG, "Exception caught: ", e);
                    }
                    catch (JSONException e) {
                        Log.e(TAG, "Exception caught: ", e);
                    }
                }
            });