Title does not appear when an item is selected in the Navigation Drawer

When I select an item in the navigation drawer the action bar does not change the title.

package br.com.isckosta.mensagenslegais;

import android.app.Activity;
import android.app.Fragment;
import android.app.FragmentManager;
import android.content.res.Configuration;
import android.os.Bundle;
import android.support.v4.app.ActionBarDrawerToggle;
import android.support.v4.widget.DrawerLayout;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import br.com.isckosta.fragment.MensagensFragment;

public class MainActivity extends Activity {
    private String[] titles;
    private DrawerLayout drawerLayout;
    private ListView listView;
    private CharSequence mTitle;
    private CharSequence drawerTitle;
    private ActionBarDrawerToggle actionBarDrawerToggle;

    /// OBSERVAÇÃO: Verificar itens não aparecendo no Navigation Drawer, background.

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

        titles = getResources().getStringArray(R.array.array_titles);
        mTitle = drawerTitle = getTitle();
        drawerLayout = (DrawerLayout) findViewById(R.id.drawer_layout);

        listView = (ListView) findViewById(R.id.left_drawer);

        listView.setAdapter(new ArrayAdapter<String>(this, R.layout.drawer_list_item, titles));
        listView.setOnItemClickListener(new DrawerItemClickListener());

        drawerLayout.setDrawerListener(actionBarDrawerToggle);
        getActionBar().setDisplayHomeAsUpEnabled(true);
        getActionBar().setHomeButtonEnabled(true);

        actionBarDrawerToggle = new ActionBarDrawerToggle(this, drawerLayout, R.drawable.ic_drawer, R.string.drawer_open, R.string.drawer_closed) {

            @Override
            public void onDrawerClosed(View drawerView) {
                super.onDrawerClosed(drawerView);
                getActionBar().setTitle(drawerTitle);
                invalidateOptionsMenu();
            }

            @Override
            public void onDrawerOpened(View drawerView) {
                super.onDrawerOpened(drawerView);
                getActionBar().setTitle(mTitle);
                invalidateOptionsMenu();
            }
        };
    }

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

        actionBarDrawerToggle.syncState();
    }

    @Override
    public void onConfigurationChanged(Configuration newConfig) {
        super.onConfigurationChanged(newConfig);

        actionBarDrawerToggle.onConfigurationChanged(newConfig);
    }

    @Override
    public boolean onPrepareOptionsMenu(Menu menu) {
        boolean drawerOpen = drawerLayout.isDrawerOpen(listView);
        menu.findItem(R.id.action_websearch).setVisible(!drawerOpen);

        return super.onPrepareOptionsMenu(menu);
    }

    private class DrawerItemClickListener implements ListView.OnItemClickListener {
        @Override
        public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
            selectItem(position);
        }
    }


    private void selectItem(int position) {
        Fragment fragment = new MensagensFragment();
        Bundle args = new Bundle();
        args.putInt(MensagensFragment.ARGS_MENSAGENS_NUMBER, position);
        fragment.setArguments(args);

        FragmentManager fragmentManager = getFragmentManager();
        fragmentManager.beginTransaction().replace(R.id.content_frame, fragment).commit();

        listView.setItemChecked(position, true);
        setTitle(titles[position]);
        drawerLayout.closeDrawer(listView);
    }

    @Override
    public void setTitle(CharSequence title) {
        mTitle = title;
        getActionBar().setTitle(title);
    }

    @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 id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        if (actionBarDrawerToggle.onOptionsItemSelected(item)) {

            return true;
        }

        return super.onOptionsItemSelected(item);
    }
}