How do I specify eg. Roboto-Medium or Roboto-Black in styles.xml

On Android 5.0 you can set Roboto Medium with sans-serif-medium.

This solution, taken from Google iosched 2014, uses sans-serif on Android pre-v21:

values/styles.xml

<style name="MyStyle">
    <item name="android:fontFamily">@string/font_fontFamily_medium</item>
</style>

values/fonts.xml

<string name="font_fontFamily_medium">sans-serif</string>

values-v21/fonts.xml

<string name="font_fontFamily_medium">sans-serif-medium</string>