pandorafms/extras/pandroid_event_viewer/res/drawable/btn_dropdown.xml

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