[Bindable]

            public var cards: Array = [ {label:"Visa", data:1},

                {label:"MasterCard", data:2}, {label:"American Express", data:3} ];

  

  [Bindable]

            public var selectedItem:Object;

 

 <mx:ComboBox dataProvider="{cards}" width="150"

            close="selectedItem=ComboBox(event.target).selectedItem"/> //前一个selectedItem 为var

        <mx:VBox width="250">

            <mx:Text  width="200" color="blue" text="Select a type of credit card."/>

            <mx:Label text="You selected: {selectedItem.label}"/>

            <mx:Label text="Data: {selectedItem.data}"/>

        </mx:VBox>