Android progressBar setVisibility () не работает

Может кто-нибудь помочь мне понять, почему progressBar.setVisibility() работает при использовании CountDownTimer, но не при загрузке async? На самом деле, первая Toast на async загрузке даже не отображается, хотя вторая onPostExecute() показывает. Ниже приведена работающая, вернее, НЕ работающая демонстрация. Большое спасибо.

Моя MainActivity:

public class MainActivity extends AppCompatActivity {

    ProgressBar progressBar;

    int[] items = { 12982418, 12998698, 12993549, 12995125, 12987537, 12993021, 12991986, 13008408, 12983417, 12986060, 12998395, 12985644, 13014731, 12986433, 12985074, 12994455, 12994262, 12986759, 13011932, 13005211, 12993521, 12987900, 12992623, 12981736, 12986649, 12991524, 13000035, 12989278, 13013868, 13009417, 13013327, 12981605, 12985768, 13000158, 13015035, 13002596, 13015944, 12997893, 12999767, 13010949, 12996835, 13013517, 13006555, 13013143, 13010016, 13005792, 13016948, 13007235, 12998343, 12987102 };
    int counter;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        progressBar = (ProgressBar) findViewById(R.id.progressBar);
        progressBar.setIndeterminate(true);
        progressBar.setKeepScreenOn(true);
        progressBar.setVisibility(View.INVISIBLE);
    }

    public void actionTimer(View view) {
        Toast.makeText(this, "starting progressBar - CountDownTimer", Toast.LENGTH_SHORT).show();
        progressBar.setVisibility(View.VISIBLE);
        new CountDownTimer(5000, 500) {
            @Override
            public void onTick(long millisUntilFinished) {
            }
            @Override
            public void onFinish() {
                progressBar.setVisibility(View.INVISIBLE);
                Toast.makeText(getApplicationContext(), "timer done", Toast.LENGTH_SHORT).show();
            }
        }.start();
    }

    public void actionJson(View view) {
        Toast.makeText(this, "starting progressBar - json fetch", Toast.LENGTH_SHORT).show();
        progressBar.setVisibility(View.VISIBLE);

        String urlTemplate = "https://hacker-news.firebaseio.com/v0/item/___ITEM_NUMBER___.json?print=pretty";
        counter = 0;

        for (int i = 0; i < items.length; i++) {
            String url = urlTemplate.replaceAll("___ITEM_NUMBER___", String.valueOf(items[i]));
            //Log.i("thisDoesNotWork", url);

            DownloadJson downloadJson = new DownloadJson();
            try {
                downloadJson.execute(url).get();
            } catch (InterruptedException e) {
                e.printStackTrace();
            } catch (ExecutionException e) {
                e.printStackTrace();
            }
        }
    }

    public class DownloadJson extends AsyncTask<String, Void, String> {

        @Override
        protected String doInBackground(String... params) {
            Log.i("DownloadJson", "url=" + params[0]);

            URL url;
            HttpURLConnection urlConnection = null;

            try {
                url = new URL(params[0]);
                urlConnection = (HttpURLConnection) url.openConnection();
                InputStream inputStream = urlConnection.getInputStream();

                BufferedReader reader = new BufferedReader(new InputStreamReader(inputStream));
                StringBuilder resultBuilder = new StringBuilder();
                String line;
                while ((line = reader.readLine()) != null) {
                    resultBuilder.append(line).append("\n");
                }
                //Log.i("DownloadJson", "resultBuilder.length()=" + resultBuilder.length());
                return resultBuilder.toString();

            } catch (Exception e) {
                e.printStackTrace();
                return "{\"status\" : \"Hacker News json download failed\"}";
            }
        }

        @Override
        public void onPostExecute(String s) {
            super.onPostExecute(s);
            counter += 1;
            if (counter == items.length) {
                progressBar.setVisibility(View.INVISIBLE);
                Toast.makeText(getApplicationContext(), "download done", Toast.LENGTH_SHORT).show();
            }
        }
    }
}

Мой XML:

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/activity_main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.plaudev.progressbar.MainActivity">

    <LinearLayout
        android:orientation="horizontal"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:gravity="center_vertical">

        <Button
            android:text="@string/timer"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_alignParentTop="true"
            android:layout_centerHorizontal="true"
            android:id="@+id/buttonTimer"
            android:layout_weight="1"
            android:onClick="actionTimer"
            android:layout_margin="25dp" />

        <Button
            android:text="@string/json"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:id="@+id/buttonJson"
            android:layout_weight="1"
            android:onClick="actionJson"
            android:layout_margin="25dp" />
    </LinearLayout>

    <ProgressBar
        style="?android:attr/progressBarStyleLarge"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerVertical="true"
        android:layout_centerHorizontal="true"
        android:id="@+id/progressBar" />
</RelativeLayout>