构建高级用户界面 使用 Tree 控件

原文地址：http://www.airia.cn/FLEX_Directory/working_with_tree/


Tree控件是一个枝和叶节点分层次的机构。树中没每一个条目叫做节点，节点既可以作为枝也可以作为叶。枝节点可以包含叶或枝节点，或者为空。一个叶节点就是一个树的末梢。本快速指南包含一些开发者在使用Treecontrols经常会遇到的一些挑战。


使用XMLLISTCOLLECTION 和ARRAYCOLLECTION对象的对比。


你也许想知道，在运行时从远程或本地得来的数据被动态修改的时候，应该使用XMLListCollection对象还是ArrayCollection对象作为Tree空间的数据提供者。


如果你使用的数据源提供成形的XML，并且，你想在Tree控件中操作 XML数据。你应该使用XMLListCollection对象作为数据提供者。当使用MXML标记时，如果数据源是XMLList对象，你应该把它绑定到XMLLsitCollection对象的source属性上，然后把 XMLListCollection对象绑定到Tree控件的dataProvider属性上。

当你想要动态改变对象值时，不要使用XMLList或XML对象直接绑定到Tree控件的dataProvider属性上。当数据源是RPC(远程过程调用)服务的lastResult属性，并且你想使用XML数据，确保RPC组件的resultFormat属性被设置成e4x，当你使用e4x结果格式，最总结果就是XMLList，可以绑定在XMLListCollection对象上。

这里有一个例子。为例数据被动态改变，使用ArrayCollection对象作为Tree控件的数据提供器。当使用MXML标记时，如果你期望动态的改变Arrayl，你不应该把Array对象直接绑定到Tree控件的dataProvider属性上。作为代替，你应该绑定Array到一个ArrayCollection对象的source属性上，然后再把ArrayCollection对象绑定到Tree控件的dataProvider属性上。


当数据源是RPC(远程过程调用)服务的lastResult对象，并且RPC组件的resultFormat属性被成object，你应该使用ArrayUtil.toArray()方法来确保对象是一个Array。然后绑定到ArrayCollection对象上，就像下边的例子所示：


<mx:ArrayCollection
    id="employeeAC"
    source= "{ArrayUtil.toArray(employeeSrv.lastResult.employees.employee)}"/>


在运行时增加和删除叶子节点


你可以在运行时为Tree控件增加或删除叶子节点。下边的例子包含的代码来实现这种改变。这个程序使用预定义的枝和叶来初始化，表现公司部门和员工。你可以向任意枝节点增加叶节点在运行时。你也可以删除预定义的叶节点和你在运行时增加的节点。


在这个例子中的XML包含两种不同的元素名字，department和employee。Tree控件的label函数，决定根据元素的类型应该显示那些文本。它使用了E4X语法来返回department的title，或者employee的name。然后，这些语法在addEmployee()和removeEmployee()中会用到。


为了增加员工到业务部门，addEmployee()方法使用E4X语法，通过title属性的值获得业务部门的节点，并把它保存到XMLList类型的变量dept中。然后，通过调用dept.appendChild()方法向操作节点添加子结点。remove方法保存当前被选择的元素到变量node中，node的类型是XML。调用node.localName()方法确定被选择的元素是否是employee节点。如果是employee节点，删除它。


例子


<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml" viewSourceURL="src/index.html">
  
    <mx:Script>
        <![CDATA[            import mx.collections.XMLListCollection;
          
            [Bindable]
            private var company:XML =
              <list>
                <department title="Finance" code="200">
                    <employee name="John H"/>
                    <employee name="Sam K"/>
                </department>
                <department title="Operations" code="400">
                    <employee name="Bill C"/>
                    <employee name="Jill W"/>
                </department>                  
                <department title="Engineering" code="300">
                    <employee name="Erin M"/>
                    <employee name="Ann B"/>
                </department>                              
              </list>;
          
            [Bindable]
            private var companyData:XMLListCollection = new XMLListCollection(company.department);
          
            private function treeLabel(item:Object):String
            {
                var node:XML = XML(item);
                if( node.localName() == "department" )
                    return node.@title;
                else
                    return node.@name;
            }
            private function addEmployee():void
            {
                var newNode:XML = <employee/>;
                newNode.@name = empName.text;
                var dept:XMLList =company.department.(@title == "Operations");
                if( dept.length() > 0 ) {
                    dept[0].appendChild(newNode);
                    empName.text = "";
                }
            }
            private function removeEmployee():void
            {
                var node:XML = XML(tree.selectedItem);
                if( node == null ) return;
                if( node.localName() != "employee" ) return;
          
                var children:XMLList = XMLList(node.parent()).children();
                for(var i:Number=0; i < children.length(); i++) {
                    if( children[i].@name == node.@name ) {
                        delete children[i];
                    }
                }
            }
        ]]>
    </mx:Script>
  
    <mx:Tree id="tree" top="72" left="50" dataProvider="{companyData}"
        labelFunction="treeLabel"
         height="224" width="179"/>
    <mx:HBox>      
        <mx:Button label="Add Operations Employee" click="addEmployee()"/><mx:TextInput id="empName"/>
    </mx:HBox>
    <mx:Button label="Remove Selected Employee" click="removeEmployee()"/>  
</mx:Application>


提示：可以通过右键flash查看官方源文件

在运行时添加一个空的枝节点


可以在运行时向Tree控件添加空的枝节点。下边的例子展示了通过数据提供器(data provider)API和数据描述器(data descriptor )API添加枝节点。通常，添加枝节点的首选途径是通过数据提供器(data provider)API。


addEmptyBranthDP()方法通过数据提供器API向使用XML数据提供器的Tree组件增加一个空节点，这个方法为新节点创建一个XML类型的变量，并且设置这个节点的isBranch属性为true来创建一个枝节点。然后这个方法调用Tree控件的dataProvider.addItemAt()方法来向Tree控件的数据提供器增加新的元素。


addEmptyBranchDP2()方法通过数据提供器API向使用对象数据提供器的Tree组件增加一个空节点，这个方法使用children属性创建一个新的对象，使用children属性能够确保isBranch()方法返回true。然后，这个方法调用Tree控件的dataProvider.addItemAt()方法来向Tree控件的数据提供器增加新的对象。


addEmptyBranchDD()方法通过数据描述器(data descripter)API。这个方法创建一个XML类型的变量，并且设置isBranch属性为true来创建一个枝节点。然后，这个方法调用Tree控件的dataDescriptor.addChildAt()方法来向Tree控件的数据描述器添加一个新的子节点。


例子


<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml" viewSourceURL="src/index.html">    <mx:Script>
        <![CDATA[
            [Bindable]
            private var dataX:XML =
                <item label="Top">
                <item label="Child One"/>
                <item label="Child Two" />
            </item>;
      
            [Bindable]
            private var dataObj:Object =
                [{label:"Top", children:
                [
                {label:"Child One"}, {label: "Child Two"}
                ]
                }];
      
            // Adding a branch by going through the Tree control's dataProvider. This is
            // the preferred method.
            // Toggling the isBranch attribute to true causes DefaultDataDescriptor.isBranch()
            // to return true and the Tree treats the node as a branch.
            private function addEmptyBranchDP():void
            {
                var newNode:XML = <item label='Middle' isBranch="true"></item>;
                xmlBound2Tree.dataProvider.addItemAt(newNode, 1);
            }
      
            // For an object graph, the key point is that the children property needs to be defined,
            // even if it is empty.
            // This causes isBranch() to return true and the Tree treats the new node as a branch.
            private function addEmptyBranchDP2():void
            {
                var newObj:Object = {label:"Middle", children:[]};
                objGraphBound2Tree.dataProvider.addItemAt(newObj, 1);
            }
      
            // Adding a branch by going through the Tree control's dataDescriptor.
            private function addEmptyBranchDD():void
            {
                var newNode:XML = <item label='Child 4' isBranch="true"></item>;
                xmlBound2Tree.dataDescriptor.addChildAt(dataX, newNode, 2, dataX);
            }
          ]]>
    </mx:Script>
    <mx:Label text="Tree with XML data"/>
    <mx:Tree id="xmlBound2Tree" dataProvider="{dataX}" labelField="@label" showRoot="true" width="200"/>
    <mx:Button label="Add Empty Branch through the dataProvider" click="addEmptyBranchDP();"/>
    <mx:Button label="Add Empty Branch through the dataDescriptor" click="addEmptyBranchDD();"/>
    <mx:Spacer height="10"/>
    <mx:Label text="Tree with object data"/>
    <mx:Tree id="objGraphBound2Tree" dataProvider="{dataObj}" width="200"/>
    <mx:Button label="Add Empty Branch through the dataProvider" click="addEmptyBranchDP2();"/>  
</mx:Application>

结果



打开树到指定的节点


默认的，Tree控件在初始化后是收缩的，你也许不确定如何初始化控件时展开数，并且选定指定的节点。下边的例子，展示了如何实现它。在这个程序中，initTree()方法，在Tree控件被创建后调用。这个方法展开Tree控件的根节点，并且设置selectedIndex属性为指定节点的索引号。


<?xml version="1.0"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml" viewSourceURL="src/index.html">    <mx:Script>
        <![CDATA[
            import flash.events.*;
            import mx.events.*;
            import mx.controls.*;
            private function initTree():void {
                XMLTree1.expandItem(MailBox.getItemAt(0), true);
                XMLTree1.selectedIndex = 2;
            }
        ]]>
    </mx:Script>
    <mx:Tree id="XMLTree1" width="150" height="170"
             labelField="@label" creationComplete="initTree();">
        <mx:XMLListCollection id="MailBox">
            <mx:XMLList>
                <node label="Mail" data="100">
                    <node label="Inbox" data="70"/>
                    <node label="Personal Folder" data="10">
                        <node label="Business" data="2"/>
                        <node label="Demo" data="3"/>
                        <node label="Saved Mail" data="5" />
                    </node>
                    <node label="Sent" data="15"/>
                    <node label="Trash" data="5"/>
                 </node>
            </mx:XMLList>
        </mx:XMLListCollection>
</mx:Tree>
</mx:Application>

结果



读取多节点名XML文档


你可以从具有多个节点名字的XML文档中组装Tree 控件。下边的例子实现了这个功能。Tree控件的数据提供者是一个XMLListCollection，它组装自一个包含folder和Pfolder元素的XMLList。Tree控件的labelField属性被设置为label属性，不管元素叫什么名字，这个属性对XMLList中的所有属性都是公共的。


例子

<?xml version="1.0"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml" viewSourceURL="src/index.html">
    <mx:Tree id="tree1" dataProvider="{MailBox}" labelField="@label" showRoot="true" width="160"/>
    <mx:XMLListCollection id="MailBox" source="{Folders}"/>
     <mx:XMLList id="Folders">
        <folder label="Mail">
            <folder label="INBOX"/>
            <folder label="Personal Folder">
                <Pfolder label="Business" />
                <Pfolder label="Demo" />
                <Pfolder label="Saved Mail" />
            </folder>

            <folder label="Sent" />
            <folder label="Trash" />
        </folder>
    </mx:XMLList>   
</mx:Application>

结果



当数据提供器更新时保持Tree控件打开


默认地，当数据提供器更新数据时Tree控件收缩。下边的例子展示了当数据提供器更新时保持Tree控件打开的方法。
在这个应用程序中，当一个用户单击Button控件时changeProvider()方法更新数据提供器。通常，这会导致Tree控件收缩。然而，Tree控件的渲染事件处理器，renderTree()方法，放置收缩的发生。当changerProvider()方法被调用，当前状态是打开的元素被保存到对象open变量中。当数据被刷新时，被命名为refreshData的Boolean类型的变量被置为true。renderTree()方法调用Tree控件的invalidateList()方法来刷新树的行。然后置refreshDate属性为false，并且重置Tree控件的打开元素属性为open对象变量，这个变量在刷新前就包含了状态是打开的元素。


例子

<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml" layout="vertical" initialize="initTree()" viewSourceURL="srcview/index.html">

    <mx:Script>
        <![CDATA[
            [Bindable]
            public var open:Object = new Object();
            [Bindable]

            public var refreshData:Boolean = false;
            [Bindable]
            public var switchObj:Object = new Object();
            [Bindable]

            public var firstObj:Object = new Object();
            [Bindable]

            public var firstObj1:Object = new Object();
            [Bindable]

            public var firstObj2:Object = new Object();
            [Bindable]

            public var provider:String = "firstObj";

            private function initTree():void

            {

                firstObj = new Object();
                firstObj.label = "Foods";
                firstObj.children = new Array();
                firstObj1.label = "Fruits";
                firstObj1.children = new Array();
                firstObj2.label = "Oranges";
                firstObj1.children[0] = firstObj2;
                firstObj.children[0] = firstObj1;
                switchObj = firstObj;
            }

            public function changeProvider():void
            {
                open = SampleTree.openItems;
                refreshData = true;
                if (provider == "firstObj")

                {
                    provider = "switchObj";
                    SampleTree.dataProvider = switchObj;
                }
                else

                {
                    provider = "firstObj";
                    SampleTree.dataProvider = firstObj;
                }
            }

            public function renderTree():void{
                if(refreshData){

                    // Refresh all rows on next update.
                    SampleTree.invalidateList();
                    refreshData = false;
                    SampleTree.openItems = open;
                    // Validate and update the properties and layout
                    // of this object and redraw it, if necessary.
                    SampleTree.validateNow();
                }

            }
        ]]>
    </mx:Script>
    <mx:Tree id="SampleTree" render="renderTree()" width="250" dataProvider="{firstObj}" labelField="label" />

    <mx:Button label="Change Data Provider" click="changeProvider()"/>
</mx:Application>

结果


项和一个树控件拖放

拖拽元素到Tree控件，和从Tree控件拖拽出元素创建一个应用程序，实现拖拽元素从Tree控件中，或到Tree控件是令人畏惧的，很明显，因为需要大量的事件处理逻辑。本节提供2个例子，来示范实现这2种功能的技术。从Tree控件中拖拽出元素下边的例子展示如何从Tree控件中拖拽元素到DataGrid控件中。Tree控件的数据提供器是XML对象。通过拖拽事件处理方法前的注释可以使你读懂整个应用程序。

例子

<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml" layout="absolute">

    <mx:Script>
        <![CDATA[
            import mx.controls.Alert;
            import mx.controls.Label;
            import mx.controls.List;
            import mx.collections.ArrayCollection;
            import mx.core.DragSource;
            import mx.controls.Tree;
            import mx.controls.DataGrid;
            import mx.controls.listClasses.ListBase;
            import mx.events.DragEvent;
            import mx.containers.Canvas;
            import mx.managers.DragManager;
            import mx.core.UIComponent;
       
            [Bindable]

            private var dataGridProvider:ArrayCollection = new ArrayCollection();
            /**
             * Handles the dragEnter event on the DataGrid control.
             * If the dragInitiator is the Tree control, then only nodes of type "restaurant"
             * are permitted to be dropped.
             * Here you can see that by examining the dragSource you can determine if
             * the control should accept the drop. The DataGrid control would not
             * know how to treat a branch+children from the Tree control, so only leaf (restaurant)
             * nodes are accepted.
             */

            private function onDragEnter( event:DragEvent ) : void

            {           
                if( event.dragInitiator is Tree ) {
                    var ds:DragSource = event.dragSource;
                    if( !ds.hasFormat("treeItems") ) return;     // no useful data

                    var items:Array = ds.dataForFormat("treeItems") as Array;
                    for(var i:Number=0; i < items.length; i++) {

                        var item:XML = XML(items[i]);
                        if( item.@type != "restaurant" ) return; // not what we want

                    }
                }
              // If the Tree control passes or the dragInitiator is not a Tree control,
             // accept the drop.
            DragManager.acceptDragDrop(UIComponent(event.currentTarget));
            }       
            /**
             * Handles the dragOver event on the DataGrid control.
             * If the dragInitiator is the Tree control, only copy is allowed. Otherwise, a move
             * or link can take place from the List control.
             */

            private function onDragOver( event:DragEvent ) : void

            {
                if( event.dragInitiator is Tree ) {
                    DragManager.showFeedback(DragManager.COPY);
                } else {

                    if (event.ctrlKey)
                    DragManager.showFeedback(DragManager.COPY);
                    else if (event.shiftKey)

                        DragManager.showFeedback(DragManager.LINK);
                    else {
                        DragManager.showFeedback(DragManager.MOVE);
                    }

                }
            }       
            /**
             * Handles the dragExit event on the drop target and just hides the
             * the drop feedback.
             */
            private function onDragExit( event:DragEvent ) : void

            {
                var dropTarget:ListBase=ListBase(event.currentTarget);  
            dropTarget.hideDropFeedback(event);
            }

            /**
             * Handles the dragDrop event on the DataGrid when the
             * drag proxy is released.
             */
            private function onGridDragDrop( event:DragEvent ) : void

            {
                var ds:DragSource = event.dragSource;
                var dropTarget:DataGrid = DataGrid(event.currentTarget);
                var arr:Array;
                if( ds.hasFormat("items") ) {

                    arr = ds.dataForFormat("items") as Array;
                } else if( ds.hasFormat("treeItems") ) {

                    arr = ds.dataForFormat("treeItems") as Array;
                }
                for(var i:Number=0; i < arr.length; i++) {

                    var node:XML = XML(arr[i]);
                    var item:Object = new Object();
                    item.label = node.@label;
                    item.type  = node.@type;
                    dataGridProvider.addItem(item);
                }

                onDragExit(event);
            }
            /**
            * Intercepts the dragComplete event on the Tree control
            * and prevents the default behavior from happening. This is necessary
            * if the item being dragged from the Tree control is dropped on a non-Tree
            * object, such as the DataGrid.
            */
            private function onTreeDragComplete(event:DragEvent):void {

                event.preventDefault();
            }       
            /**
            * Selects all of the items in the List if Ctrl+A is picked when the List control
            * has focus.
            */
            private function selectAllMaybe( event:KeyboardEvent ) : void

            {
                if( event.ctrlKey && event.keyCode == 65 ) {

                    var l:List = List(event.currentTarget);
                    var allItems:Array = new Array(l.dataProvider.length);
                    for(var i:Number=0; i < allItems.length; i++) {

                        allItems[i] = i;
                    }
                    l.selectedIndices = allItems;
                }

            }
        ]]>
    </mx:Script>
    <mx:XML id="treeData" xmlns="">
        <root>

            <node label="Massachusetts" type="state" data="MA">
                <node label="Boston" type="city" >
                    <node label="Smoke House Grill" type="restaurant" />
                    <node label="Equator" type="restaurant" />
                    <node label="Aquataine" type="restaurant" />
                    <node label="Grill 23" type="restaurant" />

                </node>
                <node label="Provincetown" type="city" >
                    <node label="Lobster Pot" type="restaurant" />
                    <node label="The Mews" type="restaurant" />
                </node>
            </node>

            <node label="California" type="state" data="CA">
                <node label="San Francisco" type="city" >
                    <node label="Frog Lane" type="restaurant" />
                </node>
            </node>
        </root>

    </mx:XML>
       
    <mx:Label x="34" y="40" text="Drag items from this Tree"/>
    <mx:Label x="34" y="55" text="(items are copied)"/>

    <mx:Tree x="34" y="81" width="181" height="189"
        dataProvider="{treeData.node}"
        labelField="@label"
        dropEnabled="false"
        dragEnabled="true"
        dragComplete="onTreeDragComplete(event)"
        dragMoveEnabled="false"
        />

    <mx:Label x="291" y="55" text="Drop items from Tree here"/>
    <mx:DataGrid x="291" y="81" height="189"
        dragEnabled="true"
        dataProvider="{dataGridProvider}"
        dragEnter="onDragEnter(event)"
        dragOver="onDragOver(event)"
        dragDrop="onGridDragDrop(event)"
        dragExit="onDragExit(event)">

        <mx:columns>
            <mx:DataGridColumn headerText="Label" dataField="label"/>
            <mx:DataGridColumn headerText="Type" dataField="type"/>

        </mx:columns>
    </mx:DataGrid>
</mx:Application>



树控件拖放

下面的示例演示如何将项从列表控件拖到树控件。 树数据提供程序是XML对象。

例子

<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml" layout="absolute">
    <mx:Script>
        <![CDATA[

            import mx.events.DragEvent;
            import mx.managers.DragManager;
            import mx.core.DragSource;
            import mx.core.UIComponent;
            import mx.controls.Tree;
            /**
             * Called as soon as the dragProxy enters the target. You can add logic
             * to determine if the target will accept the drop based on the
             * dragInitiator, the data available in the dragSource.
             * Here the drop is blindly accepted.
             */

            private function onDragEnter( event:DragEvent ) : void

            {
                DragManager.acceptDragDrop(UIComponent(event.currentTarget));
            }
            /**
             * Called while the dragProxy is over the drop target. You can
             * use this function to determine the type of feedback to show.
             * Since the List is set to allow MOVE (the item is deleted
             * once dropped), different feedback possibilities are given.
             *
             * Also, for this application, the Tree control node the dragProxy is
             * over is selected. As the dragProxy moves, the Tree control's
             * selection changes.
             *
             * For a bit more complication, the drop is being allowed
             * only over nodes whose type is NOT 'state'.
             * The feedback is removed.
             */
            private function onDragOver( event:DragEvent ) : void

            {
                var dropTarget:Tree = Tree(event.currentTarget);
                var r:int = dropTarget.calculateDropIndex(event);
                tree.selectedIndex = r;
                var node:XML = tree.selectedItem as XML;
                if( node.@type == "state" ) {

                    DragManager.showFeedback(DragManager.NONE);
                    return;
                }
                if (event.ctrlKey)

                    DragManager.showFeedback(DragManager.COPY);
                else if (event.shiftKey)
                    DragManager.showFeedback(DragManager.LINK);
                else {

                    DragManager.showFeedback(DragManager.MOVE);
                }
            }
            /**
             * Called when the dragProxy is released
             * over the drop target. The information in the dragSource
             * is extracted and processed.
             *
             * The target node is determined and
            * all of the data selected (the List has allowMultipleSection
            * set) is added.
             */
            private function onDragDrop( event:DragEvent ) : void

            {
                var ds:DragSource = event.dragSource;
                var dropTarget:Tree = Tree(event.currentTarget);
                var items:Array = ds.dataForFormat("items") as Array;
                var r:int = tree.calculateDropIndex(event);
                tree.selectedIndex = r;
                var node:XML = tree.selectedItem as XML;
                var p:*;
                // if the selected node has children (it is type==city),

                // then add the items at the beginning
                if( tree.dataDescriptor.hasChildren(node) ) {
                    p = node;
                    r = 0;
                } else {

                    p = node.parent();
                }
                for(var i:Number=0; i < items.length; i++) {

                    var insert:XML = <node />;
                    insert.@label = items[i];
                    insert.@type  = "restaurant";
                    tree.dataDescriptor.addChildAt(p, insert, r+i);
                }

            }
            /**
             * Called when the drag operation completes, whether
             * successfully or not. The tree is cleared of its
             * selection.
             */
            private function onDragComplete( event:DragEvent ) : void

            {
                tree.selectedIndex = -1;
            }       
        ]]>
    </mx:Script>   
    <mx:XML id="treeData" xmlns="">

        <root>
            <node label="Massachusetts" type="state" data="MA">
                <node label="Boston" type="city" >
                    <node label="Smoke House Grill" type="restaurant" />
                    <node label="Equator" type="restaurant" />
                    <node label="Aquataine" type="restaurant" />

                    <node label="Grill 23" type="restaurant" />
                </node>
                <node label="Provincetown" type="city" >
                    <node label="Lobster Pot" type="restaurant" />
                    <node label="The Mews" type="restaurant" />
                </node>

            </node>
            <node label="California" type="state" data="CA">
                <node label="San Francisco" type="city" >
                    <node label="Frog Lane" type="restaurant" />
                </node>
            </node>

        </root>
    </mx:XML>   
    <mx:Array id="listData">
        <mx:String>Johnny Rocket's</mx:String>

        <mx:String>Jet Pizza</mx:String>
        <mx:String>Steve's Greek</mx:String>
        <mx:String>Sonsie</mx:String>
        <mx:String>The Border Cafe</mx:String>

    </mx:Array>   
    <mx:Panel x="48" y="125" width="447" height="351" layout="absolute" title="Drag onto Tree">   
        <mx:Tree width="186" left="10" top="10" bottom="10" id="tree"
            labelField="@label"
            dataProvider="{treeData.node}"
            dropEnabled="false"
            dragMoveEnabled="false"
            dragEnter="onDragEnter(event)"
            dragOver="onDragOver(event)"
            dragDrop="onDragDrop(event)">

        </mx:Tree>       
        <mx:List width="188" height="206" right="10" bottom="10" id="list"
            allowMultipleSelection="true"
            dataProvider="{listData}"
            dragEnabled="true"
            dragMoveEnabled="true"
            dragComplete="onDragComplete(event)">

        </mx:List>       
        <mx:Text x="229" y="10" text="Drag from the list below to the tree" width="188" height="39"/>

        <mx:Label x="229" y="69" text="restaurants"/>
    </mx:Panel>   
</mx:Application>

结果