An Editable HyperLink in a TemplateField

I've kind of got into the habit of using a Repeater every time I want to display and manipulate data. However, I thought I'd play around with the GridView and DetailsView and create a simple bookmarks application. I used a HyperLinkField and set the DataNavigateUrlFields and DataTextField to the Url field in my database table. I needed to be able to edit this field so I decided to make it a template field. I added a text box to the EditItemTemplate with the text set to:

<%# Eval("Url") %>

When I tried to edit the field though, I would get an error:

This is how the complete source of the TemplateField looked:

<asp:TemplateField HeaderText="Url" SortExpression="Url">
 <EditItemTemplate>
    <asp:TextBox ID="TextBox1" runat="server" Text='<%# Eval("Url") %>'></asp:TextBox>
 </EditItemTemplate>
 <ItemTemplate>
    <asp:HyperLink ID="HyperLink1" runat="server" NavigateUrl='<%# Eval("Url") %>' Target="_blank" Text='<%# Eval("Url") %>'>
    </asp:HyperLink>
 </ItemTemplate>
</asp:TemplateField>

The reason for the error was that I was using Eval and not Bind. The Eval function is used to define one-way (read-only) binding. The Bind function is used for two-way (updatable) binding. In addition to calling Eval and Bind methods to perform data binding in a data-binding expression, you can call any publicly scoped code within the <%# and %> delimiters to execute that code and return a value during page processing. I was used to using my own publicly scoped code so was a bit unfamiliar with these two functions.

More info. on this topic at MSDN