如何使用flex mobile获取s：list标签的子项

Question

这是我的代码：

    <s:List id="list1" dataProvider="{array}" labelField="city"  width="360" height="50"  change="list1_changeHandler(event)" focusOut="list1_focusOutHandler(event)">
    <s:layout>
        <s:TileLayout horizontalAlign="center" verticalAlign="middle" paddingTop="10"  paddingLeft="10"/>
    </s:layout>
    <s:itemRenderer >
        <fx:Component>
            <s:ItemRenderer>
                <fx:Script>
                    <![CDATA[
                        override public function set data(value:Object):void {
                            sn.text = String(itemIndex+1);
                            txt.text = String(value.city);
                        }

                    ]]>
                </fx:Script>
                <s:Label id="sn"  x="15" width="15" height="30" />
                <s:Label id="txt" x="50" width="60" height="30" />
            </s:ItemRenderer>
        </fx:Component>
    </s:itemRenderer>
</s:List>

我希望在使用键盘时改变焦点，如：向上，向下

            // Event handler to handle hardware keyboard keys.
        protected function handleButtons(event:KeyboardEvent):void
        {
            if (event.keyCode == Keyboard.UP ) {
                var target:Sprite = Sprite(list1 );
                trace("clickHandler: " + target.name);
                stage.focus = target;
            }
            else if (event.keyCode == Keyboard.DOWN ) {
                var target2:Sprite = Sprite(list2 );
                trace("clickHandler: " + target2.name);
                stage.focus = target2;
            }
        }

我希望得到列表的子项，而不是列表，所以我的代码不正确：

var target:Sprite = Sprite(list1 );
                trace("clickHandler: " + target.name);
                stage.focus = target;

就像这样：

var target:Sprite = Sprite(list1.subitem );
                trace("clickHandler: " + target.name);
                stage.focus = target;

那么列表的属性是什么，我想得到子项.......

thans