Drawer icon not changing to the arrow when opened

I am just learning Android following the Head First: Android book, on the chapter 10: Drawers it shows how to create and handle a Drawer,i followed everything but as the book shows once the user opens the Drawer the hamburguer icon is supposed to change to a back arrow, my drawer opens and the clicks works fine, the only thing is that the icon does not change to the back arrow, it stays as the hamburguer icon even when i open the drawer, heres my code:

public class MainActivity extends Activity {

private String[] titles;
private ListView drawerList;
private ShareActionProvider shareActionProvider;
private DrawerLayout drawerLayout;
private ActionBarDrawerToggle drawerToggle;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    titles = getResources().getStringArray(R.array.titles);
    drawerList = (ListView) findViewById(R.id.drawer);
    drawerLayout = (DrawerLayout) findViewById(R.id.drawer_layout);
    drawerList.setAdapter(new ArrayAdapter<String>(this, android.R.layout.simple_list_item_activated_1, titles));
    drawerList.setOnItemClickListener(new DrawerItemClickListener());
    if(savedInstanceState == null){
        selectItem(0);
    }
    drawerToggle = new ActionBarDrawerToggle(this, drawerLayout, R.string.open_drawer, R.string.close_drawer){
        public void onDrawerClosed(View view){
            super.onDrawerClosed(view);
            invalidateOptionsMenu();
        }
        public void onDrawerOpened(View view){
            super.onDrawerOpened(view);
            invalidateOptionsMenu();
        }
    };
    getActionBar().setDisplayHomeAsUpEnabled(true);
    getActionBar().setHomeButtonEnabled(true);
}

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

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



@Override
public boolean onPrepareOptionsMenu(Menu menu){
    boolean drawerOpen = drawerLayout.isDrawerOpen(drawerList);
    menu.findItem(R.id.action_share).setVisible(!drawerOpen);
    return super.onPrepareOptionsMenu(menu);
}

@Override
public boolean onCreateOptionsMenu(Menu menu){
    getMenuInflater().inflate(R.menu.menu_main, menu);
    MenuItem menuItem = menu.findItem(R.id.action_share);
    shareActionProvider = (ShareActionProvider) menuItem.getActionProvider();
    setIntent("Text");
    return super.onCreateOptionsMenu(menu);
}
private void setIntent(String text){
    Intent intent = new Intent(Intent.ACTION_SEND);
    intent.setType("text/plain");
    intent.putExtra(Intent.EXTRA_TEXT, text);
    shareActionProvider.setShareIntent(intent);
}
@Override
public boolean onOptionsItemSelected(MenuItem item){
    if(drawerToggle.onOptionsItemSelected(item)){
        return true;
    }
    switch (item.getItemId()){
        case R.id.action_create_order:
            Intent intent = new Intent(this, OrderActivity.class);
            startActivity(intent);
            return true;
        case R.id.action_settings:
            return true;
        default:
            return super.onOptionsItemSelected(item);
    }
}

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;
    switch (position){
        case 1:
            fragment = new PizzaFragment();
            break;
        case 2:
            fragment = new PastaFragment();
            break;
        case 3:
            fragment = new StoresFragment();
            break;
        default:
            fragment = new TopFragment();
    }
    FragmentTransaction ft = getFragmentManager().beginTransaction();
    ft.replace(R.id.content_frame, fragment);
    ft.addToBackStack(null);
    ft.setTransition(FragmentTransaction.TRANSIT_ENTER_MASK);
    ft.commit();
    setActionBarTitle(position);
    drawerLayout.closeDrawer(drawerList);
}

private void setActionBarTitle(int position){
    String title;
    if(position == 0){
        title = getResources().getString(R.string.app_name);
    }else{
        title = titles[position];
    }
    getActionBar().setTitle(title);
}

}

After you've initialised your drawer toggle, set a drawer listener, so:

drawerLayout.setDrawerListener(drawerToggle);