How to put formitems in viewstack in flex?

How to put form items in view stack in flex?, so that i can get selected form item 开发者_JAVA百科through one comboBox

<mx:ComboBox id="cb">
    <mx:dataProvider>
        <mx:Array>
            <mx:String>Label-1</mx:String>
            <mx:String>Label-2</mx:String>
            <mx:String>Label-3</mx:String>
        </mx:Array>
    </mx:dataProvider>
</mx:ComboBox>

<mx:ViewStack id="vs" selectedIndex="{cb.selectedIndex}">
    <mx:FormItem label="Label-1">
        <mx:TextInput/>
    </mx:FormItem>
    <mx:FormItem label="Label-2">
        <mx:TextInput/>
    </mx:FormItem>
    <mx:FormItem label="Label-3">
        <mx:TextInput/>
    </mx:FormItem>
</mx:ViewStack>