A example of RelativeLayout, layout_alignParentTop, layout_alignParentBottom and layout_above

It's a example of using RelativeLayout; place a button (or any other view) on top of screen, a button on bottom of screen, and another button place related to another view.

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    >
<TextView  
    android:layout_width="fill_parent" 
    android:layout_height="wrap_content" 
    android:text="@string/hello"
    />
<RelativeLayout 
    android:layout_width="fill_parent" 
    android:layout_height="fill_parent" >
<Button 
    android:layout_width="fill_parent" 
    android:layout_height="wrap_content"
    android:layout_alignParentTop="true"
    android:text="Button on Top"
    />
<Button 
    android:id="@+id/buttonOnBottom"
    android:layout_width="fill_parent" 
    android:layout_height="wrap_content"
    android:layout_alignParentBottom="true"
    android:text="Button on Bottom"
    />
<Button
    android:layout_width="fill_parent" 
    android:layout_height="wrap_content"
    android:layout_above="@id/buttonOnBottom"
    android:text="Button Above Button on Bottom"
    />
</RelativeLayout>
</LinearLayout>