ComboBox控件的dropdown属性中的variableRowHeight属性.
示例：
代码：
<?xml version="1.0" encoding="utf-8"?>
<!-- http://blog.flexexamples.com/2008/07/04/creating-a-variable-row-height-item-renderer-on-a-combobox-control-in-flex/ -->
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml"
layout="vertical"
verticalAlign="top"
backgroundColor="white">
<mx:Script>
<![CDATA[
import mx.events.DropdownEvent;
private function comboBox_open(evt:DropdownEvent):void {
evt.currentTarget.dropdown.variableRowHeight = true;
}
]]>
</mx:Script>
<mx:Array id="arr">
<mx:Object name="Baltimore Orioles" abbr="BAL" />
<mx:Object name="Boston Red Sox" abbr="BOS" />
<mx:Object name="Chicago White Sox" abbr="CWS" />
<mx:Object name="Cleveland Indians" abbr="CLE" />
<mx:Object name="Detroit Tigers" abbr="DET" />
<mx:Object name="Kansas City Royals" abbr="KC" />
<mx:Object name="Los Angeles Angels of Anaheim" abbr="LAA" />
<mx:Object name="Minnesota Twins" abbr="MIN" />
<mx:Object name="New York Yankees" abbr="NYY" />
<mx:Object name="Oakland Athletics" abbr="OAK" />
<mx:Object name="Seattle Mariners" abbr="SEA" />
<mx:Object name="Tampa Bay Devil Rays" abbr="TB" />
<mx:Object name="Texas Rangers" abbr="TEX" />
<mx:Object name="Toronto Blue Jays" abbr="TOR" />
</mx:Array>
<mx:ComboBox id="comboBox"
dataProvider="{arr}"
width="140"
labelField="name"
open="comboBox_open(event);">
<mx:itemRenderer>
<mx:Component>
<mx:Text selectable="false"
toolTip="{data.name} ({data.abbr})" />
</mx:Component>
</mx:itemRenderer>
</mx:ComboBox>
</mx:Application>