Flex DataGrid显示行号

1. <?xml version= "1.0"  encoding= "utf-8" ?>  
2. <mx:Application xmlns:mx="http://www.adobe.com/2006/mxml"  layout= "absolute" >  
3.     <mx:DataGrid  dataProvider="{ac}"  id= "dg"  rowCount= "15" >  
4.         <mx:columns>  
5.             <mx:DataGridColumn headerText="ddd"  dataField= "col1"   labelFunction= "rowNum"  sortable= "false"   textAlign= "center"   width= "48"  backgroundColor= "#B6BDD2" />  
6.             <mx:DataGridColumn headerText="Column 2"  dataField= "col2" />  
7.             <mx:DataGridColumn headerText="Column 3"  dataField= "col3" />  
8.         </mx:columns>  
9.     </mx:DataGrid>  
10.     <mx:Script>  
11.         <![CDATA[  
12.             import  mx.controls.dataGridClasses.DataGridColumn;  
13.             import  mx.collections.ArrayCollection;  
14.             [Bindable]  
15.             public   var  ac:ArrayCollection= new  ArrayCollection([  
16.             {col1:"222" ,col2: "2" ,col3: "asdas" },  
17.             {col1:"1" ,col2: "3" ,col3: "asdas" },  
18.             {col1:"3" ,col2: "2" ,col3: "ascdas" },  
19.             {col1:"dc" ,col2: "4" ,col3: "asdas" },  
20.             {col1:"r5" ,col2: "5" ,col3: "ascdas" },  
21.             {col1:"56" ,col2: "33" ,col3: "asdas" },  
22.             {col1:"34" ,col2: "22" ,col3: "asdas" },  
23.             {col1:"76" ,col2: "33" ,col3: "ascddas" },  
24.             {col1:"62" ,col2: "53" ,col3: "sdkas" },  
25.             {col1:"89" ,col2: "65" ,col3: "sdas" },  
26.             {col1:"90" ,col2: "77" ,col3: "smdas" },  
27.             {col1:"98" ,col2: "66" ,col3: "sydas" }  
28.             ]);  
29.             /**  
30.              * 返回此item的行号  
31.              *   
32.              */   
33.             public   function  rowNum(item:Object,column:DataGridColumn):String{  
34.                    var  iIndex: int  = ac.getItemIndex(item) + 1;  
35.                         return  String(iIndex);  
36.             }  
37.         ]]>  
38.     </mx:Script>  
39. </mx:Application>