Android : GridView set header View height

I'm implementing a GridView with a Header View (GridViewWithHeaderAndFooter) . I want that the HeaderView takes 1/3 of the screen height. The problem is that in the header_view.xml I have to set a layout_height value, otherwise the view is not visible.

Here is my Activity:

    public class TestGVHeader extends Activity  {

    Context context = this;

    private GridViewWithHeaderAndFooter gridView;
    private ProductsGridViewAdapter gridViewAdapter;

    private ViewPager viewPager;
    private PagerAdapter viewPagerAdapter;



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

        gridView = (GridViewWithHeaderAndFooter) findViewById(R.id.gridView);
        LayoutInflater layoutInflater = LayoutInflater.from(this);
        View headerView = layoutInflater.inflate(R.layout.test_header_view, null);

        gridView.addHeaderView(headerView);

        gridViewAdapter = new ProductsGridViewAdapter(this, getProducts());
        gridView.setAdapter(gridViewAdapter);

        viewPager = (ViewPager) headerView.findViewById(R.id.viewpager);
        viewPagerAdapter = new CataloguePagerAdapter(context, this, this.getCatalogues());
        viewPager.setAdapter(viewPagerAdapter);

    }
}

The activity layout:

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

<in.srain.cube.views.GridViewWithHeaderAndFooter
    android:id="@+id/gridView"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:horizontalSpacing="1sp"
    android:numColumns="5"
    android:stretchMode="columnWidth"
    android:verticalSpacing="1sp"
    android:background="@android:color/white">
</in.srain.cube.views.GridViewWithHeaderAndFooter>

and the header view layout:

    <?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content">

    <android.support.v4.view.ViewPager
        android:id="@+id/viewpager"
        android:layout_width="match_parent"
        android:layout_height="450dp"
        android:layout_marginBottom="5dp"
        android:gravity="center"
    android:background="@android:color/white"/>

</FrameLayout>

Does anybody knows how to set the android:layout_height="450dp" to 1/3 of the screen height instead of a fixed value? Thanks.