In your strings.xml define:
<string-array name="array_name"> <item>Array Item One</item> <item>Array Item Two</item> <item>Array Item Three</item> </string-array>
In your layout:
<Spinner android:id="@+id/spinner" android:layout_width="fill_parent" android:layout_height="wrap_content" android:drawSelectorOnTop="true" android:entries="@array/array_name" />
References
https://stackoverflow.com/questions/4029261/populating-spinner-directly-in-the-layout-xml