IMEX.mes.pda/res/drawable/selector_checkbox2.xml

<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android">

    <item android:drawable="@drawable/checkbox2_unselect" android:state_checked="false" android:state_enabled="true"/>
    <item android:drawable="@drawable/checkbox2_selected" android:state_checked="true" android:state_enabled="true"/>
    <item android:drawable="@drawable/checkbox2_unselect"/>

</selector>