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"?>
<!--
/* //device/apps/common/res/drawable/checkbox.xml
**
** Copyright 2007, The Android Open Source Project
**
** Licensed under the Apache License, Version 2.0 (the "License");
** you may not use this file except in compliance with the License.
** You may obtain a copy of the License at
**
** http://www.apache.org/licenses/LICENSE-2.0
**
** Unless required by applicable law or agreed to in writing, software
** distributed under the License is distributed on an "AS IS" BASIS,
** WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
** See the License for the specific language governing permissions and
** limitations under the License.
*/
-->
<selector xmlns:android="http://schemas.android.com/apk/res/android">
<item android:state_focused="true" android:state_pressed="true" android:drawable="@drawable/pressed_application_background_static" />
<item android:state_focused="false" android:state_pressed="true" android:drawable="@drawable/pressed_application_background_static" />
<item android:state_focused="true" android:drawable="@drawable/focused_application_background_static" />
<item android:state_focused="false" android:drawable="@android:color/transparent" />
</selector>