Problem in getPage, return NullPointerException about smarttablayout HOT 3 CLOSED

public class MainActivity extends AppCompatActivity {

    ViewPagerItemAdapter adapter;

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

        Thread thread = new Thread() {
            @Override
            public void run() {
                try {
                    // answer
                    final String json = "";

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

                            adapter = new ViewPagerItemAdapter(ViewPagerItems.with(MainActivity.this)
                                    .add("tab1", R.layout.fragment_tab1)
                                    .add("tab2", R.layout.fragment_tab2)
                                    .add("tab3", R.layout.fragment_tab3)
                                    .create());

                            ViewPager viewPager = (ViewPager) findViewById(R.id.viewpager);
                            viewPager.setAdapter(adapter);

                            SmartTabLayout viewPagerTab = (SmartTabLayout) findViewById(R.id.viewpagertab);
                            viewPagerTab.setViewPager(viewPager);

                            // after answer
                            TextView textView1 = (TextView) adapter.getPage(0).findViewById(R.id.textView1);
                            textView1.setText("1 - ok");
                            TextView textView2 = (TextView) adapter.getPage(1).findViewById(R.id.textView2);
                            textView2.setText("2 - ok");
                            TextView textView3 = (TextView) adapter.getPage(2).findViewById(R.id.textView3);
                            textView3.setText("3 - ok");

                        }
                    });
                } catch (Exception e) {
                    //runOnUiThread(checkInternetConnection);
                    e.printStackTrace();
                }
            }
        };
        thread.start();
    }
}