import android.app.ActionBar;
import android.app.FragmentTransaction;
import android.content.Intent;
import android.os.Bundle;
import android.support.v4.app.FragmentActivity;
import android.support.v4.view.ViewPager;
import android.util.Log;
import android.view.Menu;
import android.view.MenuItem;
import com.parse.ParseAnalytics;
import com.parse.ParseUser;

import adapter.SectionPargerAdapter;


public class MainActivity extends FragmentActivity implements ActionBar.TabListener
{

    public static final String TAG = MainActivity.class.getSimpleName();

    /**
     * The {@link android.support.v4.view.PagerAdapter} that will provide
     * fragments for each of the sections. We use a
     * {@link android.support.v4.app.FragmentPagerAdapter} derivative, which
     * will keep every loaded fragment in memory. If this becomes too memory
     * intensive, it may be best to switch to a
     * {@link android.support.v4.app.FragmentStatePagerAdapter}.
     */
    SectionPargerAdapter mSectionPargerAdapter;
    ViewPager mViewPager;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);
       , ParseAnalytics.trackAppOpened(getIntent());

        ParseUser currentUser = ParseUser.getCurrentUser();

        if(currentUser == null) {

            navigateToLogin();
        } else {
            Log.i(TAG, currentUser.getUsername());
        }

        final ActionBar actionBar = getActionBar();
//        actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);


        actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);



        mSectionPargerAdapter = new SectionPargerAdapter(this, getSupportFragmentManager());

        mViewPager = (ViewPager) findViewById(R.id.pager);
        mViewPager.setAdapter(mSectionPargerAdapter);

        mViewPager.setOnPageChangeListener(new ViewPager.SimpleOnPageChangeListener(){

            @Override
            public void onPageSelected(int position) {
                actionBar.setSelectedNavigationItem(position);

                for (int i = 0; i < mSectionPargerAdapter.getCount(); i++) {
                    // Create a tab with text corresponding to the page title defined by
                    // the adapter. Also specify this Activity object, which implements
                    // the TabListener interface, as the callback (listener) for when
                    // this tab is selected.
                    actionBar.addTab(actionBar.newTab()
                            .setText( mSectionPargerAdapter.getPageTitle(i))
                            .setTabListener(MainActivity.this));}
            }
        });

    }

    @Override
    public void onTabSelected(ActionBar.Tab tab, FragmentTransaction fragmentTransaction) {
        mViewPager.setCurrentItem(tab.getPosition());
    }

    @Override
    public void onTabReselected(ActionBar.Tab tab, FragmentTransaction fragmentTransaction) {

    }

    @Override
    public void onTabUnselected(ActionBar.Tab tab, FragmentTransaction fragmentTransaction) {

    }

    private void navigateToLogin() {
        Intent intent = new Intent(this, LoginActivity.class);
        intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
        intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TASK);
        startActivity(intent);
    }


    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int itemId = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (itemId == R.id.action_logout) {
            ParseUser.logOut();
            navigateToLogin();
        }

        return super.onOptionsItemSelected(item);
    }
}

I face actionBar.setNavigationMode (ActionBar.NAVIGATION_MODE_TABS) hat eine NullPointerException erzeugt. Wie kann ich diesen Fehler beheben? Ich weiß nicht, wie ich das beheben soll. Im Tutorial-Video ist dies kein Fehler, sondern die Verwendung des Tutorials mit Eclipse. Ich benutze Android Studio. Bitte sagen Sie mir, wie ich es reparieren soll. Vielen Dank