Question

Is there a way to access the attributes of the controller action parameter currently being processed from within IModelBinder.BindModel()?

In particular, I am writing a binder for binding request data to an arbitrary Enum type (specified as a template parameter to the model binder) and I would like to specify for each controller action parameter for which I want to use this binder a name of the HTTP request value to get the Enum values from.

Example:

public ViewResult ListProjects([ParseFrom("jobListFilter")] JobListFilter filter)
{
    ...
}

and the model binder:

public class EnumBinder<T>  : IModelBinder
{
    public object BindModel(ControllerContext controllerContext,
                            ModelBindingContext bindingContext)
    {
        HttpRequestBase request = controllerContext.HttpContext.Request;

        // Get the ParseFrom attribute of the action method parameter
        // From the attribute, get the FORM field name to be parsed
        //
        string formField = GetFormFieldNameToBeParsed();

        return ConvertToEnum<T>(ReadValue(formField));
    }
}

I suspect there may possibly be another, more appropriate, point in the request workflow where I would supply the attribute value.

Answer 1

Found out how to do it using CustomModelBinderAttribute-derived class:

public class EnumModelBinderAttribute : CustomModelBinderAttribute
{
    public string Source { get; set; }
    public Type EnumType { get; set; }

    public override IModelBinder GetBinder()
    {
        Type genericBinderType = typeof(EnumBinder<>);
        Type binderType = genericBinderType.MakeGenericType(EnumType);

        return (IModelBinder) Activator.CreateInstance(binderType, this.Source);
    }
}

Now the action method looks like this:

public ViewResult ListProjects([EnumModelBinder(EnumType=typeof(JobListFilter), Source="formFieldName")] JobListFilter filter)
{
    ...
}