(My apologies if this seems verbose - trying to provide all relevant code)

I've just upgraded to VS2010, and am now having trouble trying to get a new CustomModelBinder working.

In MVC1 I would have written something like

public class AwardModelBinder: DefaultModelBinder
{
    :
    public override object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext)
    {
        // do the base binding to bind all simple types
        Award award = base.BindModel(controllerContext, bindingContext) as Award;

        // Get complex values from ValueProvider dictionary
        award.EffectiveFrom = Convert.ToDateTime(bindingContext.ValueProvider["Model.EffectiveFrom"].AttemptedValue.ToString());
        string sEffectiveTo = bindingContext.ValueProvider["Model.EffectiveTo"].AttemptedValue.ToString();
        if (sEffectiveTo.Length > 0)
            award.EffectiveTo = Convert.ToDateTime(bindingContext.ValueProvider["Model.EffectiveTo"].AttemptedValue.ToString());
        // etc

        return award;
    }
}

Of course I'd register the custom binder in Global.asax.cs:

    protected void Application_Start()
    {
        RegisterRoutes(RouteTable.Routes);

        // register custom model binders
        ModelBinders.Binders.Add(typeof(Voucher), new VoucherModelBinder(DaoFactory.UserInstance("EH1303")));
        ModelBinders.Binders.Add(typeof(AwardCriterion), new AwardCriterionModelBinder(DaoFactory.UserInstance("EH1303"), new VOPSDaoFactory()));
        ModelBinders.Binders.Add(typeof(SelectedVoucher), new SelectedVoucherModelBinder(DaoFactory.UserInstance("IT0706B")));
        ModelBinders.Binders.Add(typeof(Award), new AwardModelBinder(DaoFactory.UserInstance("IT0706B")));
    }

Now, in MVC2, I'm finding that my call to base.BindModel returns an object where everything is null, and I simply don't want to have to iterate all the form fields surfaced by the new ValueProvider.GetValue() function.

Google finds no matches for this error, so I assume I'm doing something wrong.

Here's my actual code:

My domain object (infer what you like about the encapsulated child objects - I know I'll need custom binders for those too, but the three "simple" fields (ie. base types) Id, TradingName and BusinessIncorporated are also coming back null):

public class Customer
{
    /// <summary>
    /// Initializes a new instance of the Customer class.
    /// </summary>
    public Customer() 
    {
        Applicant = new Person();
        Contact = new Person();
        BusinessContact = new ContactDetails();
        BankAccount = new BankAccount();
    }

    /// <summary>
    /// Gets or sets the unique customer identifier.
    /// </summary>
    public int Id { get; set; }

    /// <summary>
    /// Gets or sets the applicant details.
    /// </summary>
    public Person Applicant { get; set; }

    /// <summary>
    /// Gets or sets the customer's secondary contact.
    /// </summary>
    public Person Contact { get; set; }

    /// <summary>
    /// Gets or sets the trading name of the business.
    /// </summary>
    [Required(ErrorMessage = "Please enter your Business or Trading Name")]
    [StringLength(50, ErrorMessage = "A maximum of 50 characters is permitted")]
    public string TradingName { get; set; }

    /// <summary>
    /// Gets or sets the date the customer's business began trading.
    /// </summary>
    [Required(ErrorMessage = "You must supply the date your business started trading")]
    [DateRange("01/01/1900", "01/01/2020", ErrorMessage = "This date must be between {0} and {1}")]
    public DateTime BusinessIncorporated { get; set; }

    /// <summary>
    /// Gets or sets the contact details for the customer's business.
    /// </summary>
    public ContactDetails BusinessContact { get; set; }

    /// <summary>
    /// Gets or sets the customer's bank account details.
    /// </summary>
    public BankAccount BankAccount { get; set; }
}

My controller method:

    /// <summary>
    /// Saves a Customer object from the submitted application form.
    /// </summary>
    /// <param name="customer">A populate instance of the Customer class.</param>
    /// <returns>A partial view indicating success or failure.</returns>
    /// <httpmethod>POST</httpmethod>
    /// <url>/Customer/RegisterCustomerAccount</url>
    [HttpPost]
    [ValidateAntiForgeryToken]
    public ActionResult RegisterCustomerAccount(Customer customer)
    {
        if (ModelState.IsValid)
        {
            // save the Customer

            // return indication of success, or otherwise
            return PartialView();
        }
        else
        {
            ViewData.Model = customer;

            // load necessary reference data into ViewData
            ViewData["PersonTitles"] = new SelectList(ReferenceDataCache.Get("PersonTitle"), "Id", "Name");

            return PartialView("CustomerAccountRegistration", customer);
        }
    }

My custom binder:

public class CustomerModelBinder : DefaultModelBinder
{
    public override object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext)
    {
        ValueProviderResult vpResult = bindingContext
            .ValueProvider.GetValue(bindingContext.ModelName);
        // vpResult is null

        // MVC2 - ValueProvider is now an IValueProvider, not dictionary based anymore
        if (bindingContext.ValueProvider.GetValue("Model.Applicant.Title") != null)
        {
            // works
        }

        Customer customer = base.BindModel(controllerContext, bindingContext) as Customer;
        // customer instanitated with null (etc) throughout

        return customer;
    }
}

My binder registration:

    /// <summary>
    /// Application_Start is called once when the web application is first accessed.
    /// </summary>
    protected void Application_Start()
    {
        RegisterRoutes(RouteTable.Routes);

        // register custom model binders
        ModelBinders.Binders.Add(typeof(Customer), new CustomerModelBinder());

        ReferenceDataCache.Populate();
    }

... and a snippet from my view (could this be a prefix problem?)

    <div class="inputContainer">
        <label class="above" for="Model_Applicant_Title" accesskey="t"><span class="accesskey">T</span>itle<span class="mandatoryfield">*</span></label>
        <%= Html.DropDownList("Model.Applicant.Title", ViewData["PersonTitles"] as SelectList, "Select ...", 
            new { @class = "validate[required]" })%>
        <% Html.ValidationMessageFor(model => model.Applicant.Title); %>
    </div>
    <div class="inputContainer">
        <label class="above" for="Model_Applicant_Forename" accesskey="f"><span class="accesskey">F</span>orename / First name<span class="mandatoryfield">*</span></label>
        <%= Html.TextBox("Model.Applicant.Forename", Html.Encode(Model.Applicant.Forename),
                            new { @class = "validate[required,custom[onlyLetter],length[2,20]]", 
                                title="Enter your forename",
                                maxlength = 20, size = 20, autocomplete = "off",
                                  onkeypress = "return maskInput(event,re_mask_alpha);"
                            })%>
    </div>
    <div class="inputContainer">
        <label class="above" for="Model_Applicant_MiddleInitials" accesskey="i">Middle <span class="accesskey">I</span>nitial(s)</label>
        <%= Html.TextBox("Model.Applicant.MiddleInitials", Html.Encode(Model.Applicant.MiddleInitials),
                            new { @class = "validate[optional,custom[onlyLetter],length[0,8]]",
                                  title = "Please enter your middle initial(s)",
                                  maxlength = 8,
                                  size = 8,
                                  autocomplete = "off",
                                  onkeypress = "return maskInput(event,re_mask_alpha);"
                            })%>
    </div>