ASP.NET MVC WebGrid is not properly passing current parameters to the pagination links in a particular situation

Question

WebGrid pagination links work properly in all cases, except one (that I noticed).

When you use CheckBoxFor in MVC, it creates an input[type=hidden] and an input[type=check-box] for the same field so that it can handle state. So, if you have a field named X and submit your form in the GET method, you will end up with an URL like this:

http://foo.com?X=false&X=true

The default model binder can understand these multiple instances os X and figure out it's value.

The problem occurs when you try to paginate the WebGrid. It's behavior is to try catch the current request parameters and repass them in the pagination links. However, as there's more than one X, it will pass X=false,true instead of the expected X=false or X=false&X=true

That's a problem because X=false,true won't bind properly. It will trigger an exception in the model binder, prior to the beggining of the action.

Is there a way I can solve it?

EDIT:

It seems like a very specific problem but it's not. Nearly every search form with a check box will break the WebGrid pagination. (If you are using GET)

EDIT 2:

I think my only 2 options are:

• Build my own WebGrid pager that is more clever on passing parameters for pagination links
• Build my own Boolean model binder that understands false,true as valid

Answer 1

In case anybody else is suffering from the issue described, you can work around this using a custom model binder like this:

public class WebgridCheckboxWorkaroundModelBinder : DefaultModelBinder
{
    protected override void BindProperty(ControllerContext controllerContext, ModelBindingContext bindingContext, System.ComponentModel.PropertyDescriptor propertyDescriptor)
    {
        if (propertyDescriptor.PropertyType == typeof (Boolean))
        {
            var value = bindingContext.ValueProvider.GetValue(propertyDescriptor.Name);
            if (value.AttemptedValue == "true,false")
            {
                PropertyInfo prop = bindingContext.Model.GetType().GetProperty(propertyDescriptor.Name, BindingFlags.Public | BindingFlags.Instance);
                if (null != prop && prop.CanWrite)
                {
                    prop.SetValue(bindingContext.Model, true, null);
                }
                return;
            }
        }

        base.BindProperty(controllerContext, bindingContext, propertyDescriptor);
    }
}

Answer 2

An alternative to inheriting from the DefaultModelBinder would be to implement the IModelBinder interface specifically for nullable boolean values.

internal class BooleanModelBinder : IModelBinder
{
    public object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext)
    {
        // Get the raw attempted value from the value provider using the ModelName
        var param = bindingContext.ValueProvider.GetValue(bindingContext.ModelName);
        if (param != null)
        {
            var value = param.AttemptedValue;
            return value == "true,false";
        }
        return false;
    }
}

You can then add the model binding to the Global.asax or add it to the parameter like so:

public ActionResult GridRequests([ModelBinder(typeof(BooleanModelBinder))]bool? IsShowDenied, GridSortOptions sort, int? page)
{
    ...
}

Answer 3

For those who would like to implement the custom model binder in Dan's solution, but aren't sure how.

You have to register the model binder in the Global.asax file:

protected void Application_Start()
    {
        ModelBinders.Binders.Add(typeof(HomeViewModel), new WebgridCheckboxWorkaroundModelBinder());
    }

And also specify its use in your action:

public ActionResult Index([ModelBinder(typeof(WebgridCheckboxWorkaroundModelBinder))] HomeViewModel viewModel)
    {
        //code here
        return View(viewModel);
    }