title: Make a TextBox sync with SelectedValue of a DropDownList
body: <p>I have a FormView with the following ItemTemplate.  What do I have to do to make the Textbox 
  reflect the correct TypeName for the selected campaign?</p>
  
  <pre><code>&lt;asp:Label ID="campaignNameLabel" runat="server" AssociatedControlID="campaignList"&gt;Campaign Name: &lt;/asp:Label&gt;
  &lt;asp:DropDownList ID="campaignList" runat="server" Width="200px" AutoPostBack="True" DataSourceID="campaignsSqlDataSource" DataValueField="CampaignID" DataTextField="Name" SelectedValue='&lt;%# Bind("CampaignID") %&gt;'&gt;
  &lt;/asp:DropDownList&gt;
  &lt;asp:Label ID="campaignTypeLabel" runat="server"&gt;Campaign Type: &lt;/asp:Label&gt;
  &lt;asp:TextBox ID="campaignTypeText" runat="server" Width="150px" Text='&lt;%# Eval("TypeName") %&gt;'&gt;&lt;/asp:TextBox&gt;
  </code></pre>
  
  <p>ADDENDUM:  I'm trying to do this with zero code.  I can make it work if I use a separate data source for the drop-down and the detail fields in the ItemTemplate (i.e. the FormView's main data source), but I can't sync the FormView's data source with the drop-down's selection, because a ControlParameter on the FormView data source can't see control values in the ItemTemplate.</p>