Of course you can use your own names, otherwise you'd be stuck with the Android default drawables.. :)
You declare drawable names by placing a file with that name in your res/drawable
directory.
Updated, actual answer:
You need to declare a styleable attribute, in res/values/attrs.xml
(the actual filename doesn't matter, but this seems to be the convention):
<?xml version="1.0" encoding="utf-8"?>
<resources>
<declare-styleable name="MyCustomView">
<attr name="headerBackground" format="reference" />
</declare-styleable>
</resources>
Then you can assign it a value in your theme, for example:
<?xml version="1.0" encoding="utf-8"?>
<resources>
<style name="Theme" parent="android:Theme">
<item name="headerBackground">@drawable/header</item>
</style>
</resources>
Of course whatever View
you're implementing to use this newly-defined attribute has to be able to load that Drawable
and apply it. The Gallery example on the Android Developers' site is useful there.