从服务器端读取数据加载到客户端Tree控件上，如果是两层结构的话，就得在服务器端套两层List，以便和客户端的ArrayList对应。
再一点需要注意的是，第一层和第二层的labelField必须一致，比如下面： labelField都是bookName。
<mx:Tree labelField="bookName" showRoot="false" id="booksTree" dataProvider="{bookData}" width="100%" height="100%" dataDescriptor="{dataDescriptor}"/>
最重要的一点是要定义dataDescriptor 方法，实现ItreeDataDescriptor接口。这样才能实现二级菜单效果。
示例:
public class DatabaseDataDescriptor implements ITreeDataDescriptor
{
//we don't support drag and drop
public function addChildAt(node:Object, child:Object, index:int, model:Object = null):Boolean
{
return false;
}
//we don't support drag and drop
public function removeChildAt(node:Object, child:Object, index:int, model:Object=null):Boolean
{
return false;
}
//can't assume isBranch was called beforehand
public function getChildren(node:Object, model:Object = null):ICollectionView
{
if (isBranch(node, model))
{
var booktype:BookType = node as BookType;
return booktype.books;
}
return null;
}
//the node is the data
public function getData(node:Object, model:Object = null):Object
{
return node;
}
//every DatabaseVO is a branch and TableVOs are the leaves
public function isBranch(node:Object, model:Object = null):Boolean
{
return node is BookType;
}
//can't assume isBranch was called, return if tables.length > 0
public function hasChildren(node:Object, model:Object=null):Boolean
{
return isBranch(node, model)
&& BookType(node).books != null
&& BookType(node).books.length > 0;
}
}
