res/drawable/ic_keyboard_spacebar.xml

<?xml version="1.0" encoding="utf-8"?>
<!-- Copyright 2014 Google Inc. All Rights Reserved. -->
<selector xmlns:android="http://schemas.android.com/apk/res/android" >
    <item
        android:state_pressed="true"
        android:drawable="@drawable/ic_keyboard_spacebar_pressed" />
    <item
        android:drawable="@drawable/ic_keyboard_spacebar_normal" />
</selector>