Question

In my MVC 3 solution I want to have all Ids in querystring to be crypted. To decrypt URLs I inherited from DefaultModelBinder and overrided BindProperty method:

 public class CryptedIdBinder : DefaultModelBinder
{   

    protected override void BindProperty(ControllerContext controllerContext, ModelBindingContext bindingContext, System.ComponentModel.PropertyDescriptor propertyDescriptor)
    {
        if (propertyDescriptor.Name.ToLower() == "id")
        {
            propertyDescriptor.SetValue(bindingContext.Model, CryptoHelper.Decrypt(controllerContext.HttpContext.Request.Form["id"]));
            return;
        }

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

After that I set new DefaultBinder in global.asax on Application_Start:

System.Web.Mvc.ModelBinders.Binders.DefaultBinder = new CryptedIdBinder();

I didn’t inherit from IModelBinder because I want to change binding logic only for id fields in solution.

The issue is that BindProperty method is never called. What am I doning wrong?

PS. In order to be sure that I call at least BindModel method I added a peace of this code inside my custom binder, and it was hit by the debugger:

public override object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext)
    {
        return base.BindModel(controllerContext, bindingContext);
    }

Answer 1

If your models don’t have Id properties of course the BindProperty won’t be called. Because it called on the model properties. If I understood your question what you need is to transform each Id named query string parameter. In this case you need a custom value provider instead of a modelbinder. This is good article about the value providers. And it’s quite easy to write one:

public class MyValueProviderFacotry : ValueProviderFactory
{
    public override IValueProvider GetValueProvider(ControllerContext controllerContext)
    {
        return new MyValueProvider(controllerContext);
    }
}

public class MyValueProvider : IValueProvider
{
    private ControllerContext controllerContext;

    public MyValueProvider(ControllerContext controllerContext)
    {
        this.controllerContext = controllerContext;
    }

    public bool ContainsPrefix(string prefix)
    {
        return true;
    }

    public ValueProviderResult GetValue(string key)
    {
        if (key.ToLower() == "id")
        {
           var originalValue =  controllerContext.HttpContext.Request.QueryString[key]; 
           var transformedValue = CryptoHelper.Decrypt(orignalValue );
           var result = new ValueProviderResult(transformedValue,originalValue,CultureInfo.CurrentCulture);
            return result;
        }
        return null;
    }
}

In global.asax:

 protected void Application_Start()
        {
            AreaRegistration.RegisterAllAreas();
            ValueProviderFactories.Factories.Insert(4, new MyValueProviderFacotry()); //Its need to be inserted before the QueryStringValueProviderFactory
            RegisterGlobalFilters(GlobalFilters.Filters);
            RegisterRoutes(RouteTable.Routes);
        }