Question

I created a custom string object, but it does not modelbind when I post it back to the server. Is there an attribute I’m missing on the class or something?

This is the custom string class below:

public class EMailAddress
{
    private string _address;
    public EMailAddress(string address)
    {
        _address = address;
    }
    public static implicit operator EMailAddress(string address)
    {
        if (address == null)
            return null;
        return new EMailAddress(address);
    }
}

Answer 1

In order for the object to be correctly bound by the default model binder it must have a default parameterless constructor:

public class EMailAddress
{
    public string Address { get; set; }
}

if you want to use models as the one you showed you will need to write a custom model binder to handle the conversion:

public class EmailModelBinder : DefaultModelBinder
{
    public override object BindModel(
        ControllerContext controllerContext, 
        ModelBindingContext bindingContext
    )
    {
        var email = bindingContext.ValueProvider.GetValue(bindingContext.ModelName);
        if (email != null)
        {
            return new EMailAddress(email.AttemptedValue);
        }
        return new EMailAddress(string.Empty);
    }
}

which will be registered in Application_Start:

ModelBinders.Binders.Add(typeof(EMailAddress), new EmailModelBinder());

and used like this:

public class HomeController : Controller
{
    public ActionResult Index(EMailAddress email)
    {
        return View();
    }
}

Now when you query /Home/Index?email=[e-mail] the action parameter should be properly bound.

Now the question is: do you really want to write all this code when you can have a view model as the one I showed initially?