Forms Data Controls :: Can Write But Not Read CssClass Of A GridView Cell

I have a GridView where some of the BoundFields have a CssClass applied:

<asp:BoundField ... ItemStyle-CssClass="foobar">

In the rendered HTML it looks like <td class="foobar">

But when I try to read the CssClass programatically in an event like RowCreated or CheckboxChanged or PageLoad it returns nothing:

For Each row As GridViewRow In gv.Rows()
For Each cell As TableCell In row.Cells()
ltlMsg.Text += cell.CssClass
Next
Next

(gv is my GridView and ltlMsg is just a Literal for displaying the results)

If I replace cell.CssClass with cell.Text it does display results, so the code is running.

If I change it to cell.CssClass="test" it does set the class of the <td> elements. It just can't seem to read them.

I must have missed something obvious - I've tried putting it in various different events but nothing seems to work. I assume the CssClass must get set at a later point in the event cycle than I have tried. Can anyone recommend a link to documentation that shows the order in which all the events fire?

Eventually I want to use this to show or hide certain columns in the GridView based on whether a CheckBox (outside the GridView) is checked or not.