Sliding Menu doesn't show tabs

Question

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:

Activity:

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;
}
}

my Layout:

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">

<include
    android:id="@+id/toolbarMercadoria"
    layout="@layout/toolbar_default"
    android:layout_height="wrap_content"
    android:layout_width="match_parent"
    />

<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"/>

<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">

</android.support.v4.view.ViewPager>

</LinearLayout>

My Adapter:

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;
}
}

But my tabs just won't show. I don't know what I missed, so I end up with this screen:

I can really use some help :B, if there is any kind of extra information I can supply, please let me know.

Answer 1

I found my problem, it wasnt clearly in my question because i didnt posted the AbstractActivity class, where I was already calling the setContent method, so the problem was that I was calling setContent twice.. Thanks for your help.