flex tree控件添加删除节点

<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml"
    layout="vertical"
    fontSize="12">
<mx:Script>
  <![CDATA[
   import mx.controls.Alert;
   import mx.collections.XMLListCollection;
   [Bindable]
   private var company:XML=<list>
     <department name="部门 A">
      <employee name="小 A" />
      <employee name="小 B" />
     </department>
     <department name="部门 B">
      <employee name="小 C" />
      <employee name="小 D" />
     </department>
    </list>;
   [Bindable]
   private var companyData:XMLListCollection=new XMLListCollection(company.department);

   private function addNode():void
   {
    // 新建节点
    var newNode:XML=<employee/>;
    newNode.@name=empName.text;
    // 添加节点
    var xml:XML=XML(tree.selectedItem);
    if (xml.length() > 0)
    {
     xml[0].appendChild(newNode);
    }
   }

   private function removeNode():void
   {
    if (tree.selectedItem != null)
    {
     var node:XML=XML(tree.selectedItem);
     // 不能删除空节点和部门A，B
     if (node == null || node.localName() == "department")
     {
      Alert.show("不能删除空节点和部门A，B！");
      return;
     }
     // 获取当前节点的父节点下的所有子节点
     var children:XMLList=XMLList(node.parent()).children();
     // 将其转换为 XMLListCollection
     var childrenCol:XMLListCollection=new XMLListCollection(children);
     // 获取选中节点索引，并删除该节点
     var i:Number=childrenCol.getItemIndex(node);
     childrenCol.removeItemAt(i);
    }else{
     Alert.show("请选中一个节点再进行删除！");
    }
   }
  ]]>
</mx:Script>
<mx:Panel title="实现添加和删除节点"
     width="300"
     height="300"
     verticalAlign="middle"
     horizontalAlign="center">
  <mx:Tree id="tree"
     dataProvider="{companyData}"
     labelField="@name"
     height="200"
     width="230"/>
  <mx:HBox>
   <mx:TextInput id="empName"
        width="60"
        text="新节点名"/>
   <mx:Button label="添加节点"
        click="addNode();"/>
   <mx:Button label="删除节点"
        click="removeNode();"/>
  </mx:HBox>
</mx:Panel>
</mx:Application>