Android Listview does not appear

The code does not give error, it shows in design mode, but does not appear the Listview populated. I'm using the example set up on the link

    <RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent">

       <ListView
            android:id="@+id/listada"

            android:layout_width="380dp"
            android:layout_height="330dp"
            android:layout_marginTop="148dp"
            />
    </RelativeLayout>

</GridLayout>

public class ResultadosActivity extends Activity {

    @Override
    public void onCreate(Bundle savedInstance) {
        super.onCreate(savedInstance);
        setContentView(R.layout.resultados);

        ListView lista = (ListView) findViewById(R.id.lista); //listada no real

        String[] strings = new String[] { "nome1", "nome2", "nome3", "nome4" };

        ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1,strings);

        lista.setAdapter(adapter);

    }
}

results.xml , an illustrative XML that supports this view:

<LinearLayout>
    <ListView
        android:id="@+id/lista" />
</LinearLayout>

These two sections