title: Sliding Menu doesn't show tabs
body: <p>I am kind of new to Android, I am trying to implement a Sliding Menu, so I followed some tutorials and ended up with these codes:</p>
  
  <p>Activity:</p>
  
  <pre><code>public class MercadoriaFormActivity extends AbstractActivity {
  
  @Inject
  MercadoriaService mercadoriaService;
  
  @InjectView(R.id.toolbarMercadoria)
  Toolbar toolbar;
  
  @InjectView(R.id.pagerMercadoriaForm)
  ViewPager pager;
  
  @InjectView(R.id.tabsMercadoria)
  SlidingTabLayout tabs;
  
  private MercadoriaFragmentPageAdapter adapter;
  
  @Override
  public void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.activity_form_mercadoria);
      setSupportActionBar(toolbar);
      adapter = new MercadoriaFragmentPageAdapter(getSupportFragmentManager());
      pager.setAdapter(adapter);
  
      tabs.setDistributeEvenly(true);
      tabs.setCustomTabColorizer(new SlidingTabLayout.TabColorizer() {
          @Override
          public int getIndicatorColor(int position) {
              return getResources().getColor(R.color.primary_dark);
          }
      });
  
      tabs.setViewPager(pager);
  }
  
  @Override
  public boolean onCreateOptionsMenu(Menu menu) {
      getMenuInflater().inflate(R.menu.menu_mercadoria_form, menu);
      return true;
  }
  }
  </code></pre>
  
  <p>my Layout:</p>
  
  <pre><code>&lt;LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
  android:layout_width="match_parent"
  android:layout_height="match_parent"
  android:orientation="vertical"&gt;
  
  &lt;include
      android:id="@+id/toolbarMercadoria"
      layout="@layout/toolbar_default"
      android:layout_height="wrap_content"
      android:layout_width="match_parent"
      /&gt;
  
  &lt;foxy.com.br.mobile.controller.widget.SlidingTabLayout
      android:id="@+id/tabsMercadoria"
      android:layout_width="match_parent"
      android:layout_height="wrap_content"
      android:elevation="2dp"
      android:background="@color/primary"/&gt;
  
  &lt;android.support.v4.view.ViewPager
      android:id="@+id/pagerMercadoriaForm"
      android:paddingLeft="@dimen/activity_horizontal_margin"
      android:paddingRight="@dimen/activity_horizontal_margin"
      android:paddingTop="@dimen/activity_vertical_margin"
      android:paddingBottom="@dimen/activity_vertical_margin"
      android:layout_width="match_parent"
      android:layout_height="match_parent"&gt;
  
  &lt;/android.support.v4.view.ViewPager&gt;
  
  &lt;/LinearLayout&gt;
  </code></pre>
  
  <p>My Adapter: </p>
  
  <pre><code>public class MercadoriaFragmentPageAdapter extends FragmentPagerAdapter {
  
  private static final int PAGES_NUMBER = 2;
  
  private MercadoriaFormFragment mercadoriFormFragment;
  private MercadoriaAvaliacoesSensoriaisFragment avaliacoesSensoriaisFragment;
  
  public MercadoriaFragmentPageAdapter(FragmentManager fm) {
      super(fm);
  }
  
  @Override
  public Fragment getItem(int position) {
      if (position == 0) {
          return getMercadoriFormFragment();
      }
      if (position == 1) {
          return getAvaliacoesSensoriaisFragment();
      }
      return null;
  }
  
  @Override
  public int getCount() {
      return PAGES_NUMBER;
  }
  
  @Override
  public CharSequence getPageTitle(int position) {
      if (position == 0) {
          return "Dados";
      }
      if (position == 1) {
          return "A. Sensoriais";
      }
      return null;
  }
  
  public MercadoriaAvaliacoesSensoriaisFragment getAvaliacoesSensoriaisFragment() {
      if (avaliacoesSensoriaisFragment == null)
          avaliacoesSensoriaisFragment = new MercadoriaAvaliacoesSensoriaisFragment();
      return avaliacoesSensoriaisFragment;
  }
  
  public MercadoriaFormFragment getMercadoriFormFragment() {
      if (mercadoriFormFragment == null)
          mercadoriFormFragment = mercadoriFormFragment.newInstance();
      return mercadoriFormFragment;
  }
  }
  </code></pre>
  
  <p>But my tabs just won't show. I don't know what I missed, so I end up with this screen:</p>
  
  <p><img src="https://i.stack.imgur.com/HGsFi.png" alt="enter image description here"></p>
  
  <p>I can really use some help :B, if there is any kind of extra information I can supply, please let me know.</p>