如何让Flex的Tree显示水平滚动条

from http://twaver.servasoft.com/?p=3631 thanks
论坛一直有人问为何设置了twaver.controls.Tree的horizontalScrollPolicy为 ScrollPolicy.AUTO，可是还是没有横向滚动条。这是由于Adobe出于性能的考虑，没有计算maxHorizontalScrollPosition的值。本文贴出了解决方案，效果如下：

从原始Tree继承出新的类AutoSizeTree：

package com.render
{
    import flash.events.Event;
   
    import mx.controls.Alert;
    import mx.controls.Tree;
    import mx.core.ScrollPolicy;
    import mx.core.mx_internal;

    public class AutoSizeTree extends Tree
    {
        public function AutoSizeTree()
        {
            super();
            horizontalScrollPolicy = ScrollPolicy.AUTO;
        }
    
        override public function get maxHorizontalScrollPosition():Number
        {
             if (isNaN(mx_internal::_maxHorizontalScrollPosition))        
                return 0;                         
            return mx_internal::_maxHorizontalScrollPosition;     
        }          
                      
        override public function set maxHorizontalScrollPosition(value:Number):void
        {
            mx_internal::_maxHorizontalScrollPosition = value;            
            dispatchEvent(new Event("maxHorizontalScrollPositionChanged"));    
            scrollAreaChanged = true;           
            invalidateDisplayList();      
        }

        override protected function updateDisplayList(unscaledWidth:Number, unscaledHeight:Number):void
        {   
                var diffWidth:Number = measureWidthOfItems(0,0) - (unscaledWidth - viewMetrics.left - viewMetrics.right);
               
                var indentation:Number = getStyle("indentation");
           
                if (diffWidth <= 0)                  
                    maxHorizontalScrollPosition = NaN;
                else
                    maxHorizontalScrollPosition = diffWidth + indentation;                                   
                super.updateDisplayList(unscaledWidth, unscaledHeight);
        }
    }
}



如果您数据量少，性能不是大问题，不妨试一试


<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml" xmlns:cmp="com.render.*"
    height="100%" width="100%" paddingTop="0" paddingBottom="0" paddingLeft="0" paddingRight="0">
    <cmp:AutoSizeTree
            id="checkTree"
            itemRenderer="com.render.CheckTreeRenderer"
            change="updataDataGrid()"
            labelField="@label"
             width="100%" height="100%" 
             horizontalScrollPolicy="auto" >
     </cmp:AutoSizeTree>
</mx:Application>