I simply had to “encapsulate” my 2 listviews into 2 separate linearlayouts => these 2 linearlayout have a weight of 1 :
<LinearLayout android:layout_weight="1"
android:layout_height="fill_parent"
android:layout_width="fill_parent">
<ListView android:id="@+id/ListView_NASDAQ100"
android:layout_height="fill_parent"
android:layout_width="fill_parent">
</ListView>
</LinearLayout>
<LinearLayout android:layout_weight="1"
android:layout_height="fill_parent"
android:layout_width="fill_parent">
<ListView android:id="@+id/ListView_from_52w_HIGHLOW"
android:layout_height="fill_parent"
android:layout_width="fill_parent">
</ListView>
</LinearLayout>