flex tree 中渲染checkBox

package render  
{  
import flash.events.Event;  
 
import mx.controls.CheckBox;  
import mx.controls.treeClasses.TreeItemRenderer;  
import mx.controls.treeClasses.TreeListData;  
 
/** 
* 支持CheckBox的TreeItemRenderer 
* @author Montage 
*/   
public class trees extends TreeItemRenderer  
{  
    public function trees()  
    {  
        super();  
    }  
      
    /** 
     * 表示CheckBox控件从data中所取数据的字段 
     */       
    private var _selectedField:String = "selected";  
      
    protected var checkBox:CheckBox;  
      
    /** 
     * 构建CheckBox 
     */       
    override protected function createChildren():void 
    {  
        super.createChildren();  
        checkBox = new CheckBox();  
        addChild( checkBox );  
        checkBox.addEventListener(Event.CHANGE, changeHandler);  
    }  
      
    /** 
     * 点击checkbox时,更新dataProvider 
     * @param event 
     */       
    protected function changeHandler( event:Event ):void 
    {  
        if( data && data[_selectedField] != undefined )  
        {  
            data[_selectedField] = checkBox.selected;  
        }  
    }   
      
    /** 
     * 初始化控件时, 给checkbox赋值 
     */       
    override protected function commitProperties():void 
    {  
        super.commitProperties();  
        trace(data[_selectedField])  
        if( data && data[_selectedField] != undefined )  
        {  
            checkBox.selected = data[_selectedField];  
        }  
        else 
        {  
            checkBox.selected = false;  
        }  
    }  
      
    /** 
     * 重置itemRenderer的宽度 
     */       
    override protected function measure():void 
    {  
        super.measure();  
        measuredWidth += checkBox.getExplicitOrMeasuredWidth();  
    }  
      
    /** 
     * 重新排列位置, 将label后移 
     * @param unscaledWidth 
     * @param unscaledHeight 
     */       
    override protected function updateDisplayList(unscaledWidth:Number, unscaledHeight:Number):void 
    {  
        super.updateDisplayList(unscaledWidth, unscaledHeight);  
        var startx:Number = data ? TreeListData( listData ).indent : 0;  
          
        if (disclosureIcon)  
        {  
            disclosureIcon.x = startx;  
 
            startx = disclosureIcon.x + disclosureIcon.width;  
              
            disclosureIcon.setActualSize(disclosureIcon.width,  
                                         disclosureIcon.height);  
              
            disclosureIcon.visible = data ?  
                                     TreeListData( listData ).hasChildren :  
                                     false;  
        }  
          
        if (icon)  
        {  
            icon.x = startx;  
            startx = icon.x + icon.measuredWidth;  
            icon.setActualSize(icon.measuredWidth, icon.measuredHeight);  
        }  
          
        checkBox.move(startx, ( unscaledHeight - checkBox.height ) / 2 );  
          
        label.x = startx + checkBox.getExplicitOrMeasuredWidth();  
    }  
}  
}