<?xml version="1.0" encoding="utf-8"?>
<!-- http://blog.flexexamples.com/2007/12/13/programmatically-opening-and-closing-combobox-controls-in-flex/ -->
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml"
        layout="vertical"
        verticalAlign="top"
        backgroundColor="white" viewSourceURL="srcview/index.html">

    <mx:ApplicationControlBar dock="true">
        <mx:Button label="open"
                rollOver="comboBox.open();"
                enabled="false" />
        <mx:Button label="close"
                rollOver="comboBox.close();"
                enabled="false" />
    </mx:ApplicationControlBar>

    <mx:ComboBox id="comboBox"
            openDuration="2000"
            closeDuration="1000">
        <mx:dataProvider>
            <mx:Array>
                <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:dataProvider>
    </mx:ComboBox>

</mx:Application>