Custom model binding is not called when the type is NULL

Question

I have a custom structure called TimeOfDay , which is used in the view model as follows:

 public class MyViewModel { public TimeOfDay TimeOfDay { get; set; } } 

I created a custom TimeOfDayModelBinder called TimeOfDayModelBinder and registered it in Global.asax.cs as follows:

 ModelBinders.Binders.Add(typeof(TimeOfDay), new TimeOfDayModelBinder()); 

And everything works fine. However, if I change my look at this model:

 public class MyViewModel { public TimeOfDay? TimeOfDay { get; set; } // Now nullable! } 

My custom mediator is no longer called. I know that the property is no longer a TimeOfDay type, but Nullable is different. Does this mean that I have to add my own model binding twice to Global.asax.cs as follows:

 ModelBinders.Binders.Add(typeof(TimeOfDay), new TimeOfDayModelBinder()); ModelBinders.Binders.Add(typeof(TimeOfDay?), new TimeOfDayModelBinder()); 

It works, but I just don't like it. Is this really necessary in order to treat my type as nullable, or is there something I am missing?

Answer 1

In @LukeH's comment, this seems to be necessary. I think this also makes sense, since TimeOfDay and Nullable<TimeOfDay> are really two different types in the CLR. So I think I need to live with this. :-)

Answer 2

In fact, this is not the answer to your question, but an alternative solution. Maybe better ...

In MVC3, you can create an IModelBinderProvider. The implementation will be something like this:

 public class TimeOfDayModelBinderProvider : IModelBinderProvider { public IModelBinder GetBinder(Type modelType) { if(modelType == typeof(TimeOfDay) || modelType == typeof(TimeOfDay?)) { return new TimeOfDayModelBinder(); } return null; } } 

You need to register it in the DependencyResolver / IOC container or do it (at the launch of the Global.asax application):

 ModelBinderProviders.BinderProviders.Add(new TimeOfDayModelBinderProvider());