Example IModelBinderProvider implementation for ModelBinder constructor injection in MVC 3

Question

I need to wire my custom ModelBinder up to my DI container in MVC 3, but I can't get it working.

So. This is what I have: A ModelBinder with a constructor injected service.

public class ProductModelBinder : IModelBinder{
  public ProductModelBinder(IProductService productService){/*sets field*/}
  // the rest don't matter. It works.
}

My binder works fine if I add it like this:

ModelBinders.Binders.Add(typeof(Product),
     new ProductModelBinder(IoC.Resolve<IProductService>()));

But that is the old way of doing it, and I don't want that.

What I need is help on how to hook that modelbinder up to the IDependencyResolver I've registered.

According to Brad Wilson the secret is using a IModelBinderProvider implementation, but its very unclear as to how to wire that up. (in this post)

Does anyone have an example?

Answer 1

I faced the same situation when coding my MVC 3 app. I ended up with something like this:

public class ModelBinderProvider : IModelBinderProvider
{
    private static Type IfSubClassOrSame(Type subClass, Type baseClass, Type binder)
    {
        if (subClass == baseClass || subClass.IsSubclassOf(baseClass))
            return binder;
        else
            return null;
    }

    public IModelBinder GetBinder(Type modelType)
    {
        var binderType = 
            IfSubClassOrSame(modelType, typeof(xCommand), typeof(xCommandBinder)) ??
            IfSubClassOrSame(modelType, typeof(yCommand), typeof(yCommandBinder)) ?? null;

        return binderType != null ? (IModelBinder) IoC.Resolve(binderType) : null;
    }
}

Then I registered this in my IoC container (Unity in my case):

_container.RegisterType<IModelBinderProvider, ModelBinderProvider>("ModelBinderProvider", singleton());

This works for me.

Answer 2

You need to write your own IModelBinderProvider and register it with the ModelBinderProviders.BinderProviders collection:

public class YourModelBinderProvider : IModelBinderProvider {
    public IModelBinder GetBinder(Type modelType) {
         if(modelType == typeof(Product)) {
             return new ProductModelBinder(...);
         }
         return null;
    }
}

In Global.asax:

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