Android ListActivity - how to add a view below the ListView?

I'm trying to put a ProgressBar view below a ListView for a ListActivity. I want it to be always below the last row in the listView.

The ProgressBar, which is placed in a LinearLayout, does appear, as long as the list (which is filled by an adapter at runtime) is not exceeding the screen. As soon as the list is larger than the screen, the ProgressBar is no longer visible.

The layout xml looks like this:

<?xml version="1.0" encoding="utf-8"?>

<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/db1_root"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical">

<!-- Title bar -->
<LinearLayout
    style="@style/TitleBar" >
    <TextView
        style="@style/TitleBarText"
        android:text="Some title text" />
    <ImageButton
        style="@style/TitleBarAction"
        android:contentDescription="@string/description_search"
        android:src="@drawable/title_search" />
</LinearLayout>

<!--  Content -->
<LinearLayout
    android:layout_height="wrap_content"
    android:layout_width="fill_parent" >

    <ListView
        android:divider="@drawable/category_item_divider"
        android:dividerHeight="@dimen/list_divider_height"
        android:layout_height="wrap_content"
        android:id="@+id/android:list"
        android:layout_width="fill_parent"
        android:layout_weight="1" />        
    <TextView
        android:id="@+id/android:empty"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        android:text="@string/category_no_items" />                 
</LinearLayout>     

<!--  Progress bar -->
<LinearLayout
    android:layout_height="wrap_content"
    android:layout_width="wrap_content" >

    <ProgressBar
        android:id="@+id/productlist_progressbar"
        android:layout_width="wrap_content"