How to update custom ModelBinder to work with altered ModelBindingContext.ValueProvider interface in ASP.NET MVC RC2

Question

I have a custom model binder that takes a comma separated list and cleans out any empty values, then passes it along to the default model binder. This worked in ASP.NET MVC Preview 2, but when I upgraded to RC2, the below won't compile because the interface of ValueProvider only has a GetValue() method, no [] accessor. Is what I'm doing below possible through some other mechanism in the binding context? I'd rather not have to create a full blown model binder for such a simple situation. The main goal is when the values are bound to a List<SomeEnum>, any empty values are skipped.

public class EnumListModelBinder : IModelBinder
{
    public object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext)
    {
        var result = bindingContext.ValueProvider[bindingContext.ModelName];
        string[] rawValues = (string[])result.RawValue;
        var newValues = new List<string>();
        foreach (string value in rawValues)
        {
            if (!String.IsNullOrEmpty(value))
            {
                newValues.Add(value);
            }
        }

        string newValuesAttempted = String.Join(",", newValues.ToArray());
        // overwrite the ValueProviderResult with the cleaned up csv list
        // this is the part I'm not sure how to implement using the interface
        bindingContext.ValueProvider[bindingContext.ModelName] = 
           new ValueProviderResult(newValues.ToArray(), newValuesAttempted, result.Culture);

        return System.Web.Mvc.ModelBinders.Binders.DefaultBinder.BindModel(controllerContext, bindingContext);
    }
}

Answer 1

What, exactly, is wrong with using GetValue() instead of [] here? It does the same thing. But ValueProvider is an interface now, and interfaces can't have indexers. Hence, GetValue().

Change your code to:

var result = bindingContext.ValueProvider.GetValue(bindingContext.ModelName);

I'm a little surprised that the cast on the next line ever worked, though. Seems highly dependent on what the user actually submits and what the particular property type is. That's unrelated to your question, though.

Answer 2

There wasn't much of a solution here now that the ValueProvider collection is readonly. Instead I ended up using a custom model binder

http://stackoverflow.com/questions/2337374/is-there-a-way-to-have-the-defaultmodelbinder-ignore-empty-items-when-binding-to