XML,XMLList,XMLListCollection之间的关系笔记

通常情况下，你可以从服务器上为tree控件取得XML数据 ，你也可以在<mx:Tree>Tag里直接定义格式良好的XML数据。
你可以使用<mx:XML>或者<mx:XMLList>Tag在mxml里定义XML数据。
你可以将XML object直接作为一个层级数据控件的dataProvider,however,if the object changes dynamically,你应该做如下处理：
1，将XML或者XMLList objects转换为XMLListCollection；
2，通过修改XMLListCollection数据来更新原始的XML数据；
XMLListCollection支持IList和ICollectionView两个接口，所以它能实现access,sort,filter等等操作：
get,set,add,remove
同时支持IViewCursor接口，于是可以实现Cursor功能：
一个Array,ArrayCollection,ICollectionView和IViewCursor之间的关系的例子如下：
var myAC:ArrayCollection=new ArrayCollection(myArray);
var myCursor:IViewCursor=myAC.CreateCursor();
while(!myCursor.afterLast){myCursor.moveNext();}
以下例子显示了两个Tree，一个使用XML作为数据源，一个使用XMLListCollection作为数据源
Java代码

<?xml version="1.0"?><mx:Application xmlns:mx="http://www.adobe.com/2006/mxml">    <mx:XML id="capitals">        <root>            <Capitals label="U.S. State Capitals">                <capital label="AL" value="Montgomery"/>                <capital label="AK" value="Juneau"/>                <capital label="AR" value="Little Rock"/>                <capital label="AZ" value="Phoenix"/>                    </Capitals>            <Capitals label="Canadian Province Capitals">                <capital label="AB" value="Edmonton"/>                <capital label="BC" value="Victoria"/>                <capital label="MB" value="Winnipeg"/>                <capital label="NB" value="Fredericton"/>            </Capitals>        </root>    </mx:XML>    <!-- Create an XMLListCollection representing the Tree nodes.            多个capitals.Capitals组成XMLList，因为Capitals里还nest了其他  
  child elements. -->    <mx:XMLListCollection id="capitalColl" source="{capitals.Capitals}"/>    <!-- When you use an XML-based data provider with a tree you must specify        the label field, even if it is "label".        The XML object includes the root, so you must set showRoot="false".        Remember that the Tree will not, by default, reflect dynamic changes        to the XML object. -->    <mx:Tree id="Tree1" dataProvider="{capitals}" labelField="@label"showRoot="false" width="300"/>     <!-- The XMLListCollection does not include the XML root. -->    <mx:Tree id="Tree2" dataProvider="{capitalColl}" labelField="@label" width="300"/> </mx:Application> 
<?xml version="1.0"?><mx:Application xmlns:mx="http://www.adobe.com/2006/mxml">    <mx:XML id="capitals">        <root>            <Capitals label="U.S. State Capitals">                <capital label="AL" value="Montgomery"/>                <capital label="AK" value="Juneau"/>                <capital label="AR" value="Little Rock"/>                <capital label="AZ" value="Phoenix"/>                    </Capitals>            <Capitals label="Canadian Province Capitals">                <capital label="AB" value="Edmonton"/>                <capital label="BC" value="Victoria"/>                <capital label="MB" value="Winnipeg"/>                <capital label="NB" value="Fredericton"/>            </Capitals>        </root>    </mx:XML>    <!-- Create an XMLListCollection representing the Tree nodes.            多个capitals.Capitals组成XMLList，因为Capitals里还nest了其他  child elements. -->    <mx:XMLListCollection id="capitalColl" source="{capitals.Capitals}"/>    <!-- When you use an XML-based data provider with a tree you must specify        the label field, even if it is "label".        The XML object includes the root, so you must set showRoot="false".        Remember that the Tree will not, by default, reflect dynamic changes        to the XML object. -->    <mx:Tree id="Tree1" dataProvider="{capitals}" labelField="@label"showRoot="false" width="300"/>     <!-- The XMLListCollection does not include the XML root. -->    <mx:Tree id="Tree2" dataProvider="{capitalColl}" labelField="@label" width="300"/> </mx:Application>

从上面的例子可以看出，E4X标准的XML数据必须具有一个根节点，而为了阻止这个根节点在类似tree或者
Menu-Based这样的层级数据显示控件显示根节点呢，我们必须设置showRoot属性为false；
其次，当您使用XML，XMLList,XMLListCollection作为类似tree数据显示控件的数据源的时候，
你 必须明确指定这些控件的labelField 属性，即使XMLattributes里有一个label，
You must do this because you must use the @ sign to signify an attribute！
XMLListCollection提供对数据源的dynamically updates，但是XMLList和XML不行。
addItem,addItemAt,setItemAt,getItemIndex,removeItemAt
XMLListCollection的CollectionEvent事件：
Java代码

public function collectionEventHandler(event:CollectionEvent):void {  
         switch(event.kind) {  
             case CollectionEventKind.ADD:  
                 addLog("Item "+ event.location + " added");  
                 break;  
             case CollectionEventKind.REMOVE:  
                 addLog("Item "+ event.location + " removed");  
                 break;  
             case CollectionEventKind.REPLACE:  
                 addLog("Item "+ event.location + " Replaced");  
                 break;  
             case CollectionEventKind.UPDATE:  
                 addLog("Item updated");  
                 break;  
         }  
}  
<mx:ArrayCollection id="ac" 
            collectionChange="collectionEventHandler(event)" /> 
public function collectionEventHandler(event:CollectionEvent):void {         switch(event.kind) {             case CollectionEventKind.ADD:                 addLog("Item "+ event.location + " added");                 break;             case CollectionEventKind.REMOVE:                 addLog("Item "+ event.location + " removed");                 break;             case CollectionEventKind.REPLACE:                 addLog("Item "+ event.location + " Replaced");                 break;             case CollectionEventKind.UPDATE:                 addLog("Item updated");                 break;         }}<mx:ArrayCollection id="ac"            collectionChange="collectionEventHandler(event)" />

Java代码
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml" height="400">       
<mx:Script>   
<![CDATA[       
import mx.collections.XMLListCollection;      
  import mx.collections.ArrayCollection;          
  // An XML object with categorized produce.       
  [Bindable]       
  public var myData:XML=
  <catalog>              
     <category name="Meat">                   
    <product name="Buffalo" cost="4" isOrganic="No" isLowFat="Yes"/>          
    <product name="T Bone Steak" cost="6" isOrganic="No"  isLowFat="No"/>    
    <product name="Whole Chicken" cost="1.5" isOrganic="Yes" isLowFat="No"/>
  </category>         
  <category name="Vegetables">      
          <product name="Broccoli" cost="2.16" isOrganic="Yes"    isLowFat="Yes"/>      
          <product name="Vine Ripened Tomatoes" cost="1.69" isOrganic="No" isLowFat="Yes"/> 
          <product name="Yellow Peppers" cost="1.25" isOrganic="Yes"      isLowFat="Yes"/>  
  </category>
  <category name="Fruit">          
     <product name="Bananas" cost="0.95" isOrganic="Yes"  isLowFat="Yes"/>  
     <product name="Grapes" cost="1.34" isOrganic="No"   isLowFat="Yes" />       
     <product name="Strawberries" cost="2.5" isOrganic="Yes"  isLowFat="Yes"/>     
  </category>           
  </catalog>;        
   // An XMLListCollection representing the data for the shopping List.       
   [Bindable]       
   public var listDP:XMLListCollection = new XMLListCollection(new XMLList());     
         // Add the item selected in the Tree to the List XMLList data provider.       
         private function doTreeSelect():void        {           
         if (prodTree.selectedItem)       {
          listDP.addItem(prodTree.selectedItem);      
         }
         }       
         // Remove the selected in the List from the XMLList data provider.      
          private function doListRemove():void        {          
           if (prodList.selectedItem)  {             
            listDP.removeItemAt(prodList.selectedIndex); 
           }
          }  
          ]]>   
          </mx:Script>
          <mx:Tree id="prodTree" dataProvider="{myData}" width="200" showRoot="false" labelField="@name"/>
  <mx:HBox>
  <mx:Button  id="treeSelect" label="Add to List" click="doTreeSelect()"/>
  <mx:Button id="listRemove" label="Remove from List" click="doListRemove()"/>
  </mx:HBox>
<mx:List id="prodList" dataProvider="{listDP}" width="200" labelField="@name"/>
</mx:Application>