Android Linear Layout steching

I think that's a rather simple Question but I don't get it the way I want it to. I Want do do a Linear Layout in Android with 3 areas.

The Top area should have a fixed height, fill_parent width. The second, below the first, should use all the room available, fill_parent width. The third, below the second, should have fixed height, fill_parent width.

Here is what i got:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
  xmlns:android="http://schemas.android.com/apk/res/android"
  android:layout_width="fill_parent"
  android:layout_height="fill_parent"
  android:orientation="vertical"
  android:gravity="bottom"
  android:background="#ff63a920">
   <LinearLayout
android:id="@+开发者_高级运维id/top_bar"
android:layout_width="fill_parent"
android:layout_height="32dp"
>
</LinearLayout>
  <com.google.android.maps.MapView android:id="@+id/mymapView"
        android:layout_width="fill_parent" 
        android:layout_height="fill_parent"
        android:enabled="true"
        android:clickable="true"


        />
 <LinearLayout
android:id="@+id/bottombar"
android:layout_width="fill_parent"
android:layout_height="32dp"
>
</LinearLayout>
</LinearLayout>

The Problem is, that the mapview in the middle ist too big, so it pushes out the topbar.

I Hope you can help me.

Thanks to Sebastian that's what made the trick:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
  xmlns:android="http://schemas.android.com/apk/res/android"
  android:layout_width="fill_parent"
  android:layout_height="fill_parent"
  android:orientation="vertical"
  android:gravity="bottom"
  android:background="#ff63a920">
   <LinearLayout
android:id="@+id/top_bar"
android:layout_width="fill_parent"
android:layout_height="32dp"
android:layout_weight="0"
>
</LinearLayout>
  <com.google.android.maps.MapView android:id="@+id/mymapView"
        android:layout_width="fill_parent" 
        android:layout_height="fill_parent"
        android:enabled="true"
        android:clickable="true"
        android:layout_weight="1"

        />
 <LinearLayout
android:id="@+id/bottombar"
android:layout_width="fill_parent"
android:layout_height="32dp"
android:layout_weight="0"
>
</LinearLayout>
</LinearLayout>

there is a software called DroidDraw. (freeware) use it and it will generate the XML code autmatically for u.

Hope that helps