Determining if a drop down menu is open in a Spark DropDownList control in Flex 4

<?xml version="1.0" encoding="utf-8"?>
<!-- http://blog.flexexamples.com/2009/08/06/determining-if-a-drop-down-menu-is-open-in-a-spark-dropdownlist-control-in-flex-4/ -->
<s:Application name="Spark_DropDownList_isDropDownOpen_test"
        xmlns:fx="http://ns.adobe.com/mxml/2009"
        xmlns:s="library://ns.adobe.com/flex/spark"
        xmlns:mx="library://ns.adobe.com/flex/halo">
 
    <fx:Script>
        <![CDATA[
            protected function init():void {
                checkBox.selected = ddl.isDropDownOpen;
            }
        ]]>
    </fx:Script>
 
    <s:CheckBox id="checkBox"
            label="isDropDownOpen"
            mouseEnabled="false"
            tabEnabled="false"
            creationComplete="init()"
            x="10" y="10" />
 
    <s:DropDownList id="ddl"
            requireSelection="true"
            width="150"
            horizontalCenter="0"
            top="40"
            open="init();"
            close="init();">
        <s:dataProvider>
            <s:ArrayList source="[The,Quick,Orange,Fox,Jumps,Over,The,Lazy,Dog]" />
        </s:dataProvider>
    </s:DropDownList>
 
</s:Application>