Nested datagrid : setting focus on the inside datagrid

I have a datagrid with a single column rendered with another datagrid. I'm doing this to implement a rowspan-like display (with a hbox beneath the child datagrid) showing messages under each row. When I tab and reach the end of a row, I want the focus to pass to the next row i.e the next child datagrid and on a specific cell of that row. This is the simplified code calling the renderer :

<mx:DataGrid width="100%"
                 showHeaders="false"
                 selectable="false"
                 id="ParentDatagrid"
                 dataProvider="{arrayActs}"
                 paddingBottom="0" paddingTop="0"
                 variableRowHeight="true">
        <mx:columns>
            <mx:DataGridColumn itemRenderer="components.ColumnRendererDatagrid"/>
        </mx:columns>
    </mx:DataGrid>

And the renderer (ColumnRendererDatagrid) code :

<mx:DataGrid 
    id="dgLocal" width="100%" height="23" borderSides=""
    dataProvider=开发者_如何学Go"{data}" showHeaders="false"
    editable="true" selectable="false">
    <mx:columns>
        <mx:DataGridColumn />
        <mx:DataGridColumn />
        <mx:DataGridColumn />
        <mx:DataGridColumn />
        <mx:DataGridColumn />
    </mx:columns>
</mx:DataGrid>
<mx:HRule width="100%" />
<mx:Label id="message" text="Error Message" width="100%" />

For the moment, I'm using the following snippet in ColumnRendererDatagrid to check when tabbing reaches the end of the row and bubble up the event :

if(dgLocal.editedItemPosition.columnIndex == 13){
                dispatchEvent(new Event(MOVE_FOCUS_DOWN, true));

From there I'm struggling on how to drill down into the renderer to set the focus once the higher component get this event. Any help would be really appreciated. Thx

---

Ok, here is the solution I came up with. This is the code in the parent's event handler (handling the MOVE_FOCUS_DOWN):

//Find the postition of the item that sent the event :
for each( var row:Object in ParentDatagrid.dataProvider ) {     
                if( (event.target as ColumnRendererDatagrid).data == row) {
                    break;
                }
                i++;
            } 

//Get the renderer of the next item :
  var render:IListItemRenderer = ParentDatagrid.itemToItemRenderer(arrayActes.getItemAt(i+1));
  (render as ColumnRendererDatagrid).dgLocal.editedItemPosition = {rowIndex:0, columnIndex:1}

(obviously checks should be made in real code to see if the next object exists) which is of type ColumnRendererDatagrid. From there I just set the focus/editing position.