<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml"
        layout="vertical"
        verticalAlign="top"
        backgroundColor="white" viewSourceURL="srcview/index.html">

    <mx:Script>
        <![CDATA[
            import mx.events.DropdownEvent;

            private function comboBox_open(evt:DropdownEvent):void {
                comboBox.dropdown.selectable = checkBox.selected;
            }
        ]]>
    </mx:Script>

    <mx:Array id="arr">
        <mx:Object label="One" />
        <mx:Object label="Two" />
        <mx:Object label="Three" />
        <mx:Object label="Four" />
        <mx:Object label="Five" />
        <mx:Object label="Six" />
    </mx:Array>

    <mx:ApplicationControlBar dock="true">
        <mx:CheckBox id="checkBox"
                label="selectable:"
                labelPlacement="left"
                selected="false" />
    </mx:ApplicationControlBar>

    <mx:ComboBox id="comboBox"
            prompt="Please select an item"
            dataProvider="[One,Two,Three,Four,Five,Six]"
            open="comboBox_open(event);" />

</mx:Application>