Explicitly specify the default property
<?xml version="1.0"?> <mx:Application xmlns:mx="http://www.adobe.com/2006/mxml"> <mx:ComboBox> <mx:dataProvider> <mx:ArrayCollection> <mx:String>AK</mx:String> <mx:String>AL</mx:String> <mx:String>AR</mx:String> </mx:ArrayCollection> </mx:dataProvider> </mx:ComboBox> </mx:Application>