Nesting layouts

This layout for some reason doesn't work as expected. The two text boxes are overlapping, despite the fact that I'm using the layout_below tag. What am I doing wrong?

<?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:background="@android:color/white"&开发者_如何学Cgt;

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

        <TextView android:id="@+id/homeButton"
            android:layout_width="wrap_content" 
            android:layout_height="wrap_content" 
            android:text="Dashboard" />

    </LinearLayout>

    <RelativeLayout android:id="@+id/dashboard"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:layout_below="@id/actionbar">

        <TextView android:id="@+id/libraryButton"
            android:layout_width="wrap_content" 
            android:layout_height="wrap_content"
            android:text="Dashboard Area" />

    </RelativeLayout>

</LinearLayout>

Sure it does not ... You have to enclose both layouts in a parent layout eg.

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    ...
    android:orientation="vertical"
/>
    <LinearLayout
    ...
    >
    </LinearLayout>

    <RelativeLayout
    ...
    >
    </RelativeLayout>
</LinearLayout>

It might however be better to use RelativeLayout and arrange the views using parameters provided.