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

<?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：

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)" />

<?xml version="1.0"><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>