Como ordenar os itens de uma List em ordem alfabética ascendente

<?xml version="1.0" encoding="iso-8859-1"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml">

  <mx:Panel id="painel" title="Estudos" status="Active" 
     height="300" width="200" paddingTop="10" 
     paddingLeft="10" paddingRight="10" 
     paddingBottom="10">

    <mx:List id="listaNomes" width="150" rowCount="4"
      dataProvider="{mNomes}"/>

    <mx:Button label="Ordem Alfabética Ascendente" 
       click="ordenar();"/>

  </mx:Panel>

  <mx:Script>
    <![CDATA[
      import mx.collections.ArrayCollection;
      import mx.collections.SortField;
      import mx.collections.Sort;      
     
      [Bindable]
      public var mNomes:ArrayCollection = 
        new ArrayCollection(["Osmar", "Carlos", 
          "Fernanda", "Igor", "Amélia"]);

      private function ordenar():void{
        var sort:Sort = new Sort();
        sort.fields = [new SortField(null, true)];
        mNomes.sort = sort;
        mNomes.refresh();          
      }
    ]]>
  </mx:Script>  

</mx:Application>