flex中combobox绑定xml数据后取不到data
问题如题，代码如下

<?xml version="1.0" encoding="utf-8"?>
<mx:WindowedApplication xmlns:mx="http://www.adobe.com/2006/mxml" layout="absolute" initialize="init()">
<mx:Script>
<![CDATA[
import mx.collections.ArrayCollection;
import mx.collections.XMLListCollection;

[Bindable]
private var xml:XML = <root>
 <item name="datagrid" data="1"/>
 <item name="combobox" data="2"/>
 <item name="List" data="3"/>
</root>;
[Bindable]
private var xmlLc:XMLListCollection;

[Bindable]
private var arrC:ArrayCollection;

private function init():void
{
xmlLc = new XMLListCollection(xml.children());

arrC = new ArrayCollection();
arrC.addItem({label:"aa",data:"1"});
arrC.addItem({label:"bb",data:"2"});
arrC.addItem({label:"cc",data:"3"});
}

private function show():void
{
trace(cb.value);
trace(cb.selectedItem.data);
trace("111");
}
]]>
</mx:Script>
<mx:ComboBox id="cb" x="196" y="263" editable="false" dataProvider="{xml.item}" labelField="@name" change="show()"></mx:ComboBox>

</mx:WindowedApplication>

显示结果如下，为了显示取不到数据我在数据输出后面加了一个输出，先看输出截图
[img=http://my.csdn.net/my/album/detail/1210773][/img]
请问这是什么情况，在init()里试着绑定XMLListCollection也取不到值，只有ArrayCollection能取到值，请大家帮我分析下。
[解决办法]
private function show():void
{
var obj:Object = cb.selectedItem;
Alert(obj.@data)
}