MVC2 binding not working for custom type

Question

I've converted a string property in my model to a class that has implicit operators to and from my custom type EngNum . I did this so that all occurences of this type would have my custom editor, even though the type should behave and be used like a string.

My problem is that the property is no-longer bound correctly to my model even though the value is there in the Form on POST.

See below for my EngNum type:

public class EngNum
{
    private string internalString;

    public EngNum() { }

    public EngNum(string number)
    {
        internalString = number;
    }

    public static implicit operator string(EngNumnumber)
    {
        return number == null ? null : number.internalString;
    }

    public static implicit operator EngNum(string number)
    {
        return new EngineerNumber() { internalString = number };
    }
}

And here's now its displayed in the view:

<%= Html.EditorFor(m => m.EngineerNumber) %>

And here's the editor for it:

<%@ Control Language="C#" Inherits="System.Web.Mvc.ViewUserControl<ThreeSixtyScheduling.Models.EngineerNumber>" %>
<%@ Import Namespace="ThreeSixtyScheduling.BLL.Utilities" %>
<%= Html.ComboBoxFor(m => m,
                     new { @class = "EngineerNumber" },
                     Url.Action("MasternautEngineers", "Data", new { area = (string)null }),
                     Model, 0) %>

ComboBoxFor renders a TextBoxFor along with some jquery.

Before I took this code from the view and put it into the editor it worked fine.

What do I have to do to get my property bound properly on postback?

---

The ModelState in the controller action has the following exception associated with the EngineerNumber property:

{System.InvalidOperationException: The parameter conversion from type 'System.String' to type 'ThreeSixtyScheduling.Models.EngNum' failed because no type converter can convert between these types. at System.Web.Mvc.ValueProviderResult.ConvertSimpleType(CultureInfo culture, Object value, Type destinationType) at System.Web.Mvc.ValueProviderResult.UnwrapPossibleArrayType(CultureInfo culture, Object value, Type destinationType) at System.Web.Mvc.ValueProviderResult.ConvertTo(Type type, CultureInfo culture) at System.Web.Mvc.DefaultModelBinder.ConvertProviderResult(ModelStateDictionary modelState, String modelStateKey, ValueProviderResult valueProviderResult, Type destinationType)}

---

The controller method (and type of model):

[HttpPost]
public ActionResult CreateStockcheckJob(CreateStockcheckJobModel viewModel)

public class CreateStockcheckJobModel
{
    [Required]
    [DisplayName("Engineer Number")]
    public EngNum EngineerNumber { get; set; }

    [Required]
    [DisplayName("Date and Time")]
    public DateTime DateAndTime { get; set; }

    public bool JobCreated { get; set; }

    public CreateStockcheckJobModel()
    {
        DateAndTime = DateTime.Today.WithTimeOfDay(8, 0, 0);
    }
}

Code for the ComboBoxFor :

    public static MvcHtmlString ComboBoxFor<TModel, TProperty>(this HtmlHelper<TModel> htmlHelper,
                                                               Expression<Func<TModel, TProperty>> expression,
                                                               object htmlProperties,
                                                               string ajaxJSONLocation,
                                                               string selectedValue,
                                                               int minLength)
    {
        return ComboBoxFor(htmlHelper, expression, htmlProperties, ajaxJSONLocation, selectedValue, minLength, false, string.Empty);
    }

    public static MvcHtmlString ComboBoxFor<TModel, TProperty>(this HtmlHelper<TModel> htmlHelper,
                                                               Expression<Func<TModel, TProperty>> expression,
                                                               object htmlProperties,
                                                               string ajaxJSONLocation,
                                                               string selectedValue,
                                                               int minLength,
                                                               bool hideId,
                                                               string selectCallbackScript)
    {
        var textboxHTML = htmlHelper.TextBoxFor(expression, htmlProperties);

        var scriptString = @"<script type=""text/javascript"">
$(function() {
    " + (string.IsNullOrEmpty(selectedValue) ? "$('#" + htmlHelper.IdFor(expression) + @"').val('')" : string.Empty) + @"
    $.getJSON('" + ajaxJSONLocation + @"', function(result) {

        $('#" + htmlHelper.IdFor(expression) + @"').autocomplete({
                                                                     minLength: " + minLength.ToString() + @",
                                                                     source: function(request, response) {
                                                                                 dataArray = new Array();
                                                                                 $.each(result, function(k, v) {
                                                                                    if (v.value.toUpperCase().indexOf(request.term.toUpperCase()) != -1 ||
                                                                                        v.desc.toUpperCase().indexOf(request.term.toUpperCase()) != -1) {
                                                                                        dataArray.push(v);
                                                                                    }
                                                                                 });
                                                                                 response(dataArray);
                                                                     },
                                                                     focus: function(event, ui) {},
                                                                     select: function(event, ui) {
                                                                     $('#" + htmlHelper.IdFor(expression) + @"').val( ui.item.value );
                                                                     " + selectCallbackScript + @"
                                                                     return false; }
                                                            })
                                                   .data(""autocomplete"")._renderItem = function (ul, item) {
                                                        return $(""<li></li>"")
                                                                .data(""item.autocomplete"", item)
                                                                .append(""<a>"" + " + (hideId ? string.Empty : @"item.value + ""<br/>"" + ") + @"""<span>"" + item.desc + ""</span></a>"")
                                                                .appendTo(ul);
                                                   };
    });
});
</script>";

        return MvcHtmlString.Create(textboxHTML.ToString() + scriptString);
    }

Answer 1

The model binder is not going to call your custom implicit operator. You need to have a public property with the same name or write a custom model binder. Usually you don't need to use implicit operator on view models.

Answer 2

You need to add a type converter to your class through TypeConverterAttribute . This type converter will be used by ASP.NET MVC to convert strings to your type.