asp.net 2.0 GridView update question

I have a GridView that I want to leave in update mode all the time.

Code:
<asp:GridView ID="gvOrders" runat="server" AutoGenerateColumns="False"
    DataSourceID="SqlDataSource1" DataKeyNames="order_number" >
<Columns>
<asp:TemplateField HeaderText="Product ID">
<ItemTemplate>
<asp:TextBox ID="Label8" runat="server" Text='<%# Bind("product_id") %>'></asp:TextBox >
</ItemTemplate>
</asp:TemplateField>
</asp:GridView>                        

<asp:SqlDataSource ID="SqlDataSource1" runat="server"
        ConnectionString="<%$ ConnectionStrings:dbSales %>"
        SelectCommand="pr_get_audiobook_order_by_order_id" SelectCommandType="StoredProcedure">
<SelectParameters>
<asp:ControlParameter ControlID="txtOrderId" Name="order_id" PropertyName="Text"  Type="Int32" />        </SelectParameters>
</asp:SqlDataSource>

Now, in the code behind, there is an event that is fired when the person clicks "get order" that loads the gridview based on the text typed into the order text box... all trivial stuff.  However, the end user would like, when the grid view is started, for it to automatically go into edit mode ON ALL ROWS (hence putting the bind on a text box, rather than a label).  When they are done editing, they would like to click ONE button to update ALL changed items.  No problem, right?  I create a button which fires an event, handle the event in the code behind, yank the values out of my GridView and run a StoredProceedure to update each row in the database.

The problem is that I can't seem to get the data out of the GridView.  For all intents and purposes it's empty when I go to read it. I have tried addressing each row and cell
gvOrders.Rows[i].Cells[j].Text  but no matter what I put in i or j it always returns "".

What am I doing wrong?  Is there more code you need to see?