Datagrid itemRenderer/itemEditor trouble

Question

I have a datagrid in a Flex project, the data grid has an XML file as the source (contents below), now due to the way it is formatted (I cannot change this) some of the data I want to display is inside a tag that isnt at the initial array level. Here is the file:
<?xml version="1.0" encoding="utf-8" ?>
<Categories>
<Category>
  <CategoryName>Cat 1</CategoryName>
  <CategoryLink>http://www.google.com</CategoryLink>
  <CategoryData>
   <CategoryDescription>This is the description of category 1</CategoryDescription>
   <CategoryHeader>My Category Title 1</CategoryHeader>
   <CategoryNumber>1</CategoryNumber>
  </CategoryData>
</Category>
</Categories>
I need to display CategoryName, CategoryLink, CategoryData.CategoryDescription, CategoryData.CategoryNumber.
Now I blindly dropped the datagrid into the project and bound it to the data source, I get the following returned for CategoryData:
[object CategoryData_type]
Not much use, but with what appears to be a hack I changed the code for the column to read dataField="CategoryData.CategoryDescription", and hooray it works. I didnt realise at the time that this was wrong, and when I dropped in an itemEditor things went wrong. When the datagrids load they display the correct data, but then when you try to edit any of the child property fields you get the following error:
ReferenceError: Error #1069: Property CategoryData.CategoryDescription not found on valueObjects.Category_type and there is no default value.
I have looked up the error and I realise that it means that there is no value for CategoryData.CategoryDescription, but if I can display it why can i not edit it! What do I have to do to make this work?
Anyway, here is the code, it shows the default bound datagrid, a second datagrid with the hack applied, and a third hacked datagrid with an itemRenderer and itemEditor on the number columns
Can you please take a look and tell me what I did wrong, well more to the point, if there is a doc that explains how to deal with XML like this then please point me at it.
I did try changing the return type for ANY of the columns, but this fails, I also tried a labelFunction, but again I can get the [object CategoryData_type] to display, but I get the null reference exception as the datagrid loads if I try to get to the child props.
Here is the Flex code:
<?xml version="1.0" encoding="utf-8"?>
<s:Application xmlns:fx="http://ns.adobe.com/mxml/2009"
      xmlns:s="library://ns.adobe.com/flex/spark"
      xmlns:mx="library://ns.adobe.com/flex/mx"
      xmlns:categories="services.categories.*"
      minWidth="955" minHeight="600">
<fx:Script>
  <![CDATA[
   import mx.controls.Alert;
   import mx.events.FlexEvent;
   protected function dataGrid_creationCompleteHandler(event:FlexEvent):void
    getDataResult.token = categories.getData();
   protected function lftest(item:Object, column:GridColumn):String
    var t:String = item.CategoryData;
    return t;
  ]]>
</fx:Script>
<fx:Declarations>
  <s:CallResponder id="getDataResult"/>
  <categories:Categories id="categories"
          fault="Alert.show(event.fault.faultString + '\n' + event.fault.faultDetail)"
          showBusyCursor="true"/>
  <!-- Place non-visual elements (e.g., services, value objects) here -->
</fx:Declarations>
<s:DataGrid id="dataGrid" x="10" y="10" width="684"
    creationComplete="dataGrid_creationCompleteHandler(event)" editable="true"
    requestedRowCount="4">
  <s:columns>
   <s:ArrayList>
    <s:GridColumn width="100" dataField="CategoryName" headerText="CategoryName"></s:GridColumn>
    <s:GridColumn width="100" dataField="CategoryLink" headerText="CategoryLink"></s:GridColumn>
    <s:GridColumn width="180" dataField="CategoryData" headerText="CategoryData"></s:GridColumn>
   </s:ArrayList>
  </s:columns>
  <s:typicalItem>
   <fx:Object CategoryData="CategoryData1" CategoryLink="CategoryLink1"
        CategoryName="CategoryName1"></fx:Object>
  </s:typicalItem>
  <s:AsyncListView list="{getDataResult.lastResult}"/>
</s:DataGrid>
<s:DataGrid id="dataGrid2" x="10" y="147" width="684" editable="true" requestedRowCount="4">
  <s:columns>
   <s:ArrayList>
    <s:GridColumn width="100" dataField="CategoryName" headerText="CategoryName"></s:GridColumn>
    <s:GridColumn width="100" dataField="CategoryLink" headerText="CategoryLink"></s:GridColumn>
    <s:GridColumn width="180" dataField="CategoryData" headerText="CategoryData"></s:GridColumn>
    <s:GridColumn dataField="CategoryData.CategoryDescription" headerText="Desc"></s:GridColumn>
    <s:GridColumn dataField="CategoryData.CategoryHeader" headerText="Head"></s:GridColumn>
    <s:GridColumn dataField="CategoryData.CategoryNumber" headerText="Num"></s:GridColumn>
   </s:ArrayList>
  </s:columns>
  <s:typicalItem>
   <fx:Object CategoryData="CategoryData1" CategoryLink="CategoryLink1"
        CategoryName="CategoryName1"></fx:Object>
  </s:typicalItem>
  <s:AsyncListView list="{getDataResult.lastResult}"/>
</s:DataGrid>
<s:DataGrid id="dataGrid3" x="10" y="284" width="684" editable="true" requestedRowCount="4">
  <s:columns>
   <s:ArrayList>
    <s:GridColumn width="100" dataField="CategoryName" headerText="CategoryName"></s:GridColumn>
    <s:GridColumn width="100" dataField="CategoryLink" headerText="CategoryLink"></s:GridColumn>
    <s:GridColumn width="180" dataField="CategoryData" headerText="CategoryData"></s:GridColumn>
    <s:GridColumn headerText="Number">
     <s:itemRenderer>
      <fx:Component>
       <s:GridItemRenderer>
        <s:NumericStepper value="{data.CategoryData.CategoryNumber}" />
       </s:GridItemRenderer>
      </fx:Component>
     </s:itemRenderer>
    </s:GridColumn>
    <s:GridColumn dataField="CategoryData.CategoryNumber" headerText="Number">
     <s:itemEditor>
      <fx:Component>
       <s:GridItemEditor>
        <s:NumericStepper value="{data.CategoryData.CategoryNumber}" />
       </s:GridItemEditor>
      </fx:Component>
     </s:itemEditor>
    </s:GridColumn>
   </s:ArrayList>
  </s:columns>
  <s:typicalItem>
   <fx:Object CategoryData="CategoryData1" CategoryLink="CategoryLink1"
        CategoryName="CategoryName1"></fx:Object>
  </s:typicalItem>
  <s:AsyncListView list="{getDataResult.lastResult}"/>
</s:DataGrid>
</s:Application>
All and any advice welcome.
Shaine

Answer 1

One last try, I now know for sure that the data in the file is loading, I created a labelFunction on the CategoryDescription column that looks like this:
protected function dispData(item:Object, column:GridColumn):String
    var t:Object = item.CategoryData;
    var s:String = item.CategoryData.CategoryDescription;
    return s;
Because it returns s, which I now know is undefined (which is the problem!) I managed to get a debug output. As you can see the value of t is the categorydata, and it appears to have the 3 values I need to get access to, but I have no idea how to do this. I also changed the function to read:
protected function dispData(item:Object, column:GridColumn):String
var t:Object = item.CategoryData;
var s:String = t.CategoryDescription;
return s;
But this undefines t and s! Very confused
this test2 (@d2e10a1)
item valueObjects.Category_type (@91f8a51)
[inherited]
column spark.components.gridClasses.GridColumn (@d61b239)
t valueObjects.CategoryData_type (@91f8c11)
[inherited]
  _cacheInitialized_isValid false
  CategoryDescription "This is the description of category 1"
  CategoryHeader "My Category Title 1"
  CategoryNumber "1"
  _changedObjects mx.collections.ArrayCollection (@d5d9e41)
  _changeWatcherArray [] (@cfab061)
  _dminternal_model _CategoryData_typeEntityMetadata (@d4286a1)
  _doValidationCacheOfCategoryDescription null
  _doValidationCacheOfCategoryHeader null
  _doValidationCacheOfCategoryNumber null
  _doValidationLastValOfCategoryDescription null
  _doValidationLastValOfCategoryHeader null
  _doValidationLastValOfCategoryNumber null
  _internal_CategoryDescription "This is the description of category 1"
  _internal_CategoryHeader "My Category Title 1"
  _internal_CategoryNumber "1"
  _invalidConstraints [] (@ca50fd9)
  invalidConstraints_der <setter>
  _isValid false
  isValid_der <setter>
  managingService <setter>
  _managingService null
  _model _CategoryData_typeEntityMetadata (@d4286a1)
  _validationFailureMessages [] (@cfab0b1)
s undefined
As always all help welcome.
Shaine
Message was edited after a oops moment by: ProcessEndNow