Flex DataGrid中列绑定ComboBox

<?xml version="1.0" encoding="utf-8"?>  
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml" layout="absolute">  
 <mx:Script>  
        <![CDATA[  
            import mx.collections.ArrayCollection;  
            public var datas:ArrayCollection = new ArrayCollection([1,2,3,4]);  
            private var gridDatas:ArrayCollection = new ArrayCollection([  
                {col1:1,col2:2,col3:3},{col1:1,col3:3}  
            ]);  
        ]]>  
    </mx:Script>  
    <mx:DataGrid x="89" y="111" width="350" height="145" dataProvider="{gridDatas}">  
        <mx:columns>  
            <mx:DataGridColumn headerText="Column 1" dataField="col1"/>  
            <mx:DataGridColumn headerText="Column 2" dataField="col2"/>  
            <mx:DataGridColumn headerText="Column 3" dataField="col3">  
                <mx:itemRenderer>  
                    <mx:Component>  
                        <mx:ComboBox dataProvider="{outerDocument.datas}"/>  
                    </mx:Component>  
                </mx:itemRenderer>  
            </mx:DataGridColumn>  
        </mx:columns>  
    </mx:DataGrid>  
</mx:Application>