Custom Model Binder for List nested inside a wrapper model

Question

I have the following model:

public class SidebarViewModel
{
    public SidebarViewModel()
    {
        Filters = new List<FilterViewModel>();
    }

    public List<FilterViewModel> Filters { get; set; }
}

And each Filter looks like this:

public abstract class FilterViewModel
{
    [Required]
    public string Value { get; set; }

    [HiddenInput(DisplayValue = false)]
    public bool Visible { get; set; }

    [HiddenInput(DisplayValue = false)]
    public abstract string DisplayName { get; }

    [HiddenInput(DisplayValue = false)]
    public string ModelType { get { return GetType().Name; } }
}

And there are filter subtypes that look like this:

public class TextFilter : FilterViewModel
{
    public override string DisplayName
    {
        get { return "Some Name Here"; }
    }
}

When the post occurs, the entire SidebarViewModel should be posted to the controller:

[HttpPost]
public ActionResult Filter(SidebarViewModel sidebar)
{
    // Stuff here.
}

In order to get the SidebarViewModel to bind, I tried writing a custom ModelBinder for FilterViewModel objects:

public class FilterModelBinder : DefaultModelBinder
{
    protected override object CreateModel(ControllerContext controllerContext, ModelBindingContext bindingContext, Type modelType)
    {
        var modelName = bindingContext.ModelName;
        var filterTypeValue = bindingContext.ValueProvider.GetValue(modelName + ".ModelType");
        var filterType = Type.GetType(filterTypeValue.ToString(), true);
        var model = Activator.CreateInstance(filterType);

        bindingContext.ModelMetadata = ModelMetadataProviders.Current.GetMetadataForType(() => model, filterType);

        return model;
    }
}

And registered that ModelBinder in Global.asax.cs:

ModelBinders.Binders.Add(typeof(FilterViewModel), new FilterModelBinder());

Finally, the view:

@model SidebarViewModel
@using (Ajax.BeginForm("Filter", SessionVars.ControllerName, new AjaxOptions
{
    UpdateTargetId = "tool-wrapper",
    LoadingElementId = "loading-image",
    HttpMethod = "POST"
}))
{
    <fieldset>
        @Html.EditorFor(m => m.Filters)

        <div class="form-actions">
            <button type="submit">Submit Options</button>
        </div>
    </fieldset>
}

And EditorTemplate:

@model FilterViewModel

<div class="control-group">
    @Html.Label(Model.DisplayName, new { @class = "control-label" })

    <div class="controls">
        @Html.TextBoxFor(m => m.Value)

        @Html.HiddenFor(m => m.DisplayName)
        @Html.HiddenFor(m => m.ModelType)
        @Html.HiddenFor(m => m.Visible)
    </div>
</div>

The problem is that when the sidebar is posted, the FilterModelBinder is never called. Do I need another custom model binder for SidebarViewModel? If so, how would I call the FilterModelBinder for each filter in the sidebar's list?

Answer 1

Ah, it ended up being an issue with my RuntimeRoute registration. There was an invalid one in there, and removing it fixed my binding issue.