sample/src/main/res/drawable-nodpi/buttonstate_transparent.xml

<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android">
    <item android:state_focused="true" android:state_pressed="false"
          android:drawable="@drawable/button_transparent_pressed" />
    <item android:state_focused="true" android:state_pressed="true"
          android:drawable="@drawable/button_transparent_pressed" />
    <item android:state_focused="false" android:state_pressed="true"
          android:drawable="@drawable/button_transparent_pressed" />
    <item android:drawable="@drawable/transparent"/>
</selector>