<mx:Application
xmlns:mx="http://www.adobe.com/2006/mxml"
layout="horizontal">
<mx:ComboBox dataProvider="{myDP}"
labelFunction="getFullName"/>
<mx:Script>
<![CDATA[
import mx.collections.ArrayCollection;
[Bindable]
private var myDP:ArrayCollection =
new ArrayCollection([
{id:1,fName:"Lucky", lName:"Luke"},
{id:2, fName:"Bart", lName:"Simpson"}]);
private function getFullName(item:Object):String{
return item.fName + " " + item.lName;
}

]]>
</mx:Script>
</mx:Application>