Flex labelFunction 用法

        <mx:VBox horizontalAlign="left" height="100%" width="100%">
            <mx:Canvas id="cavApproverList" width="100%" height="100%">
                <mx:VBox id="boxApp"  top="2" width="100%" height="100%"  left="2" right="2" bottom="2" >
                    <mx:DataGrid  id="expenseItemADG" selectable="false" dataProvider="{approverList}" rowCount="7" sortableColumns="false">
                        <mx:columns>
                            <mx:DataGridColumn dataField="StepOrder" headerText="" width="20" />
                            <mx:DataGridColumn dataField="ApproverName" headerText="Name"  width="200" sortable="false"  />
                            <mx:DataGridColumn dataField="ApproverGrade" headerText="Grade" width="200" sortable="false"  />
                            <mx:DataGridColumn dataField="ApprovedDate" headerText="Status" width="300" sortable="false" labelFunction="StatuFunction" />
                        </mx:columns>
                    </mx:DataGrid>

                </mx:VBox>
            </mx:Canvas>
        </mx:VBox>    

            public function StatuFunction(item:Object, column:DataGridColumn):String
            {
                var df:DateFormatter = new DateFormatter();
                df.formatString = "YYYY-MM-DD JJ:NN:SS";

                var value:String = "Approved at " + df.format(item.ApprovedDate).toString();

                return value;
            }