The file containing the source code shown below is located in the corresponding directory in <sdk>/samples/android-<version>/...
<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android">
<item android:state_pressed="true"
android:drawable="@drawable/refresh_pressed" /> <!-- pressed -->
<item android:drawable="@drawable/refresh" /> <!-- default -->
</selector>