ASP.net MVC Model failing to recognise values - asp.net-mvc

Question

As part of my current project I've blundered into an enormous MVC web form that I know relatively little about, and am having to do some fairly serious debugging on it. I have plenty of WebForms experience but little with MVC so please forgive me if the following isn't clear, or is asking silly questions.
Part of the form is a custom .ascx control which gets information from another URL and limits what the user can put into that section of the form based on that information. All the form elements can be turned on and off. If you turn this particular form element on, fill it in and submit then the ModelState fails its validation check, complaining that its missing a required value. The form is returned with the problematic element switched on, but no values in the boxes. If you don't switch on this particular element, the ModelState validates properly.
I know enough about MVC to understand that the mapping between form elements and the model occurs under the hood. However this makes it very difficult to debug. I really have no idea what the problem is or, worse, how to go about investigating what the cause is. Any suggestions on either front would be greatly appreciated.
EDIT: Some code
//start to deal with specialist form user controls
case "ViewData.Customer.CustomFieldTypes.BlackWhiteListConfigViewData ":
if (Model.Visible)
{ %>
<div class="formItem">
<label>
<% Html.RenderPartial("~/Views/Shared/EditorTemplates/BlackWhiteListConfigViewData.ascx"); %>
</div>
<% }
else
{ %>
<%= Html.HiddenFor(m => Model.Value) %>
<% }
b break;
And the binding code:
switch (fieldType)
{
case FeatureFieldFactory.BlackWhiteListConfigElTypeName:
{
// create a new default model binder, and tell it which type we actually want it to bind.
BlackWhiteListConfigViewData model = new BlackWhiteListConfigViewData();
bindingContext.ModelMetadata =
ModelMetadataProviders.Current.GetMetadataForType(() => model, typeof(BlackWhiteListConfigViewData));
return base.BindModel(controllerContext, bindingContext);
}
EDIT: BlackWhiteListConfigViewData.ascx code
if (Model.Visible)
{ %>
<script type="text/javascript">
$(cpContext.CurrentService()).bind('onServiceAttributesReady', function (context) {
$(document).ready(function () {
$("#js-hook-BlackWhiteListLoading").hide();
if (context.target.AttributeNames().length === 0) {
$("#js-hook-AddBlackWhiteListEntry").hide();
$("#js-hook-BlackWhiteListConfigTable").hide();
$("#js-hook-BlackWhiteListMessage").html('There are no attribute types present in the catalogue. The Black and White lists can be configured once the catalogue is loaded.');
$("#js-hook-BlackWhiteListMessage").show();
}
else {
$("#js-hook-BlackWhiteListMessage").hide();
$("#js-hook-AddBlackWhiteListEntry").show();
$("#js-hook-BlackWhiteListConfigTable").show();
}
});
});
$(cpContext.CurrentService()).bind('onServiceAttributesError', function (context) {
$(document).ready(function () {
$("#js-hook-BlackWhiteListLoading").hide();
$("#js-hook-AddBlackWhiteListEntry").hide();
$("#js-hook-BlackWhiteListConfigTable").hide();
$("#js-hook-BlackWhiteListMessage").html('No attribute types retrieved from service API. The Black and White lists can be configured when a Build has been completed and service API is accessible.');
$("#js-hook-BlackWhiteListMessage").show();
});
});
cpContext.CurrentService().getAttributes();
</script>
<div class="formItem narrow blackWhiteListConfig">
<% using (Html.BeginCollectionItem("fields"))
{
Model.Value = "n/a";
%>
<%= Html.HiddenFor(m => Model.Id) %>
<%= Html.HiddenFor(m => Model.Type) %>
<%= Html.HiddenFor(m => Model.Name) %>
<%= Html.HiddenFor(m => Model.Visible) %>
<%= Html.HiddenFor(m => Model.DisplayName) %>
<%= Html.HiddenFor(m => Model.Value) %>
<table id="js-hook-BlackWhiteListConfigTable" class="configTable" style="display:none">
<thead>
<tr><th class="configTableColumn">Key Attribute Type</th><th class="configTableColumn">Key Value</th><th class="transparent"></th><th class="configTableColumn">Related Attribute Type</th><th class="configTableColumn">Related Attribute Value</th><th class="configTableColumn narrow">Black</th><th class="configTableColumn narrow">White</th><th class="transparent" style="width:20px"></th></tr>
</thead>
<tbody class="blackWhiteListRows">
<% foreach (BlackWhiteListEntryViewData entry in Model.Entries)
{ %>
<%= Html.EditorForNested(e => entry) %>
<% } %>
</tbody>
</table>
<hr />
<p id="js-hook-AddBlackWhiteListEntry" class="clear" style="display:none">Add another entry</p>
<p id="js-hook-BlackWhiteListMessage" class="clear" style="display:none">There are no attribute types present in the catalogue. The Black and White lists can be configured once the catalogue is loaded.</p>
<img id="js-hook-BlackWhiteListLoading" src="<%=Links.Content.images.content_loading_gif %>" alt="Loading Black and White list configuration..."
style="" class="clear" />
<%= Html.ValidationMessageFor(m => Model) %>
<% } %>
Model.Value) %>
Cheers,
Matt

Answer 1

Try replacing:
<% Html.RenderPartial("~/Views/Shared/EditorTemplates/BlackWhiteListConfigViewData.ascx"); %>
with:
<%= Html.EditorForModel() %>
or if your model type is not BlackWhiteListConfigViewData you could specify it:
<%= Html.EditorForModel("BlackWhiteListConfigViewData") %>
Also inside your editor template you seem to be using some custom helpers such as Html.EditorForNested. Make sure your input field names respect the conventions for binding to a list.