ASP.NET Html Extension not firing? - asp.net-mvc-2

Question

I have a couple of Extension classes, borrowed from various places, and they both work - individually. When I try to use both on the same page it appears one does not work. Here is the setup:
MVC 2 (no path for upgrading it to MVC 3 or 4)
HtmlPrefixScopeExtensions - http://blog.stevensanderson.com/2010/01/28/editing-a-variable-length-list-aspnet-mvc-2-style/
FileBoxHtmlHelperExtension -
http://forums.asp.net/p/1566760/4033836.aspx
The .ascx page code looks like:
<%# Control Language="C#" AutoEventWireup="true" Inherits="System.Web.Mvc.ViewUserControl<PB.WMATA.ApplicationServices.ViewModels.Files.CIPDocumentAndFile>" %>
<%# Import Namespace="Company.Web.Extensions"%>
<div class="editorRow">
<% using(Html.BeginCollectionItem("docs")) { %>
<%= Html.Hidden("CIPDocument.Id", (Model != null) ? Model.Id : 0) %>
<label for="CIPNumber">Document Name:</label>
<%= Html.TextBox("CIPNumber", (Model != null) ? Model.CIPNumber : "", new { #size = "50", #maxlength = "255" })%>
<%= Html.ValidationMessage("CIPNumber")%>
<% if (Model != null && Model.FileName != null && Model.FileName.Length > 0) { %>
<label>Current File:</label>
<%= Model.FileName %>
<% } else { %>
<label>
File Upload:
<%= Html.FileBoxFor(m => m.HttpPostedFileBase) %>
</label>
<% } %>
delete
<% } %>
</div>
The output for this looks like:
<div class="editorRow">
<input name="docs.index" autocomplete="off" value="1809201d-2143-4da3-ba34-e443a332c516" type="hidden">
<input id="docs_1809201d-2143-4da3-ba34-e443a332c516__CIPDocument_Id" name="docs[1809201d-2143-4da3-ba34-e443a332c516].CIPDocument.Id" value="0" type="hidden">
<label for="CIPNumber">
Document Name:
</label>
<input id="docs_1809201d-2143-4da3-ba34-e443a332c516__CIPNumber" maxlength="255" name="docs[1809201d-2143-4da3-ba34-e443a332c516].CIPNumber" size="50" value="" type="text">
<label>
File Upload:
<input id="HttpPostedFileBase" name="HttpPostedFileBase" type="file">
</label>
<a href="#" class="deleteRow">
delete
</a>
</div>
Notice the FileUpload control did not get the HtmlPrefixScope. I expected it to be:
<input id="docs_1809201d-2143-4da3-ba34-e443a332c516__HttpPostedFileBase" name="docs[1809201d-2143-4da3-ba34-e443a332c516].HttpPostedFileBase" type="file">
I am not quite savvy enough with extensions to see what may be going on. I suspect that the collection extension is being handled before it tries to handle the filebox extension. Any ideas?

Answer 1

After digging in it turns out that I needed to get at the TemplateInfo.HtmlFieldPrefix value as the Html.BeginCollectionItem("docs") call had altered it. Was really simple once I understood the lifecycle of the TemplateInfo object. Here is the altered code for the FileBox & FileBoxFor code pieces:
public static MvcHtmlString FileBox(this HtmlHelper htmlHelper, string name, IDictionary<String, Object> htmlAttributes)
{
// If the HtmlFieldPrefix has been altered (see HtmlPrefixScopeExtensions class!!) then this will work with it...
var htmlFieldPrefix = htmlHelper.ViewData.TemplateInfo.HtmlFieldPrefix;
name = (!string.IsNullOrEmpty(htmlFieldPrefix) ? string.Format("{0}.", htmlFieldPrefix) : "") + name;
var tagBuilder = new TagBuilder("input");
tagBuilder.MergeAttributes(htmlAttributes);
tagBuilder.MergeAttribute("type", "file", true);
tagBuilder.MergeAttribute("name", name, true);
tagBuilder.GenerateId(name);
ModelState modelState;
if (htmlHelper.ViewData.ModelState.TryGetValue(name, out modelState))
{
if (modelState.Errors.Count > 0)
{
tagBuilder.AddCssClass(HtmlHelper.ValidationInputCssClassName);
}
}
return MvcHtmlString.Create(tagBuilder.ToString(TagRenderMode.SelfClosing));
}