Databinding to taxtbox value

[hericles]

Hey,
I've been working on a product display page that lists product info and images via a repeater control. That all works fine. What I'm doing now is adding some new functionality that uses a link button to send the product code clicked on to the server (via AJAX, to add it to the order).
I'm trying to send the quantity entered into a textbox as the command argument of the link button but can't find out how to access the textbox value.

So far I have:
<div class="quantityDiv" id="Q<%# DataBinder.Eval(Container.DataItem, "product_id")%>">
No:&nbsp;&nbsp;
<asp:TextBox Rows="5" size="5" ID="tbQuantity" runat="server" />
&nbsp;&nbsp;
<asp:LinkButton ID="lbAdd" OnCommand="addToOrder" CommandArgument='<%# DataBinder.Eval(Container.DataItem, "product_id")%>' CommandName='<%# Eval(Page, "tbQuantity" )%>' runat="server" Text="Add" OnClientClick="hideQuantDiv();">
</asp:LinkButton>

Its only the Eval for the textbox that is giving me trouble. From hints on the net I've gathered that databinding of the page is possible but I haven't found out how to do it.

Any advice?

Thank you,