How can I use Client ID within a server control? - asp.net

Question

I was able to do the following in a repeater and it works just fine:
<asp:TextBox ID="txtOtherPartyName" Text='<%# Eval("Name") %>' runat="server" />
<asp:RequiredFieldValidator ID="reqLoss" ControlToValidate="txtOtherPartyName"
data-valmsg-for='<%# Container.FindControl("txtOtherPartyName").ClientID%>'
Display="Dynamic" ErrorMessage="Name of party involved is required." runat="server" />
The data-valmsg-for attribute in the required validator rendered the server control id just fine. How can I do the same for a control that sits on a page and is not within a repeater? I tried similar things without any luck.
Update
So here's what I'm looking to do exactly:
<asp:Textbox id="txtTest" runat="server" />
<asp:RequiredFieldValidator id="reqTest" data-valmsg-for=**[i want the html rendered id of "txtTest" here]** runat="server" />

Answer 1

You can bind that custom attribute to the control's client id in the code behind.
butthead.Attributes.Add("data-custom-prop", beavis.ClientID);

Answer 2

In the Repeater you used databinding syntax (<%# ... %>), but that doesn't apply in this case. You should be able to set the attribute like this:
data-valmsg-for='<%= TextBox1.ClientID %>'
Why are you adding custom attributes to the validators in the first place though, if you don't mind me asking? What purpose does it serve that can't be achieved through other means?
EDIT
Have you considered building your list of control IDs in code-behind beforehand, and storing it somewhere? Could something like this be a starting point?:
var controlList = Page.Validators.OfType<BaseValidator>()
.Select(v => Page.FindControl(v.ControlToValidate).ClientID).ToList();
EDIT
Expanding on that idea, you can serialize the list to JSON using the JavaScriptSerializer (System.Web.Script.Serialization):
//initialize the javascript serializer
var serializer = new JavaScriptSerializer();
//retrieve all of the validators on the page and store the client ids in a list
var controlList = Page.Validators.OfType<BaseValidator>()
.Select(v => Page.FindControl(v.ControlToValidate).ClientID).ToList();
//serialize the control id list and register the script block on the page
Page.ClientScript.RegisterClientScriptBlock(this.GetType(), "data", string.Format("var data = {0}", serializer.Serialize(controlList)), true);
Depending on how complex the form is, you may need to create a recursive function to find all of the controls, but hopefully this demonstrates the concept.