How to configure dependency injection with ASP.NET MVC 3 RTM - dependency-injection

Question

I am upgrading a web app from ASP.NET 3 Preview 1 to the RTM and I am confused by the updated approach to dependency injection. I am using StructureMap for this but that's not really relevant to my question. Previously all I needed to do was as follows:
x.For<IControllerFactory>().Use<DefaultControllerFactory>();
x.For<IServiceLocator>().Use(MvcServiceLocator.Current);
Now it seems like I need to provide implementations of IControllerActivator, IViewPageActivator and ModelMetadataProvider because otherwise I get an error from StructureMap because MVC tries to locate them using the dependency resolver. From a look at the MVC source there do not seem to be public default implementations. Am I missing something in setting these up? Surely these should be configured by convention?
Examples of what needs configuring and how with StructureMap would be appreciated. For reference I am currently using the following ugly kludge which forces MVC to use its internal defaults:
x.For<IControllerFactory>().Use<DefaultControllerFactory>();
x.For<IDependencyResolver>().Use(() => DependencyResolver.Current);
x.For<IControllerActivator>().Use(() => null);
x.For<IViewPageActivator>().Use(() => null);
x.For<ModelMetadataProvider>().Use(ModelMetadataProviders.Current);
EDIT: Just to be clear I have a working StructureMap implementation of the Dependency Resolver - the issue is why MVC is complaining about all these interfaces not being configured in the container.

Answer 1

I was able to get StructureMap to work with ASP.NET MVC3 by creating a Dependency Resolver(IDependencyResolver) class, then registering that class in the global.asax. I have not fully tested this code. But, it has been working without any issues in two applications.
StructureMapDependencyResolver.cs
using System.Linq;
using System.Web.Mvc;
using StructureMap;
namespace SomeNameSpace
{
public class StructureMapDependencyResolver : IDependencyResolver
{
private readonly IContainer container;
public StructureMapDependencyResolver(IContainer container)
{
this.container = container;
}
public object GetService(System.Type serviceType)
{
try
{
return this.container.GetInstance(serviceType);
}
catch
{
return null;
}
}
public System.Collections.Generic.IEnumerable<object> GetServices(System.Type serviceType)
{
return this.container.GetAllInstances<object>()
.Where(s => s.GetType() == serviceType);
}
}
}
Global.asax.cs
public static void RegisterGlobalFilters(GlobalFilterCollection filters)
{
filters.Add(new HandleErrorAttribute());
}
public static void RegisterRoutes(RouteCollection routes)
{
routes.IgnoreRoute("{resource}.axd/{*pathInfo}");
routes.MapRoute(
"Default", // Route name
"{controller}/{action}/{id}", // URL with parameters
new { controller = "Home", action = "Index", id = UrlParameter.Optional } // Parameter defaults
);
}
protected void Application_Start()
{
AreaRegistration.RegisterAllAreas();
DependencyResolver.SetResolver(new StructureMapDependencyResolver(InitContainer()));
RegisterGlobalFilters(GlobalFilters.Filters);
RegisterRoutes(RouteTable.Routes);
}
private static IContainer InitContainer()
{
ObjectFactory.Initialize(x =>
{
x.Scan(y =>
{
y.WithDefaultConventions();
y.AssembliesFromApplicationBaseDirectory();
y.LookForRegistries();
});
});
return ObjectFactory.Container;
}

Answer 2

I've figured this out thanks to the link #Michael Carman posted in a comment on his answer. I'm not sure of the etiquette here as to whether that warrants accepting his actual answer as it wasn't quite right (I've given him +1 vote) but I thought I'd post my own answer to explain exactly what the issue was.
The problem was down to a combination of my implementation of IDependencyResolver and my container configuration. Originally I had:
public class StructureMapDependencyResolver : IDependencyResolver
{
public object GetService(Type serviceType)
{
return ObjectFactory.GetInstance(serviceType);
}
public IEnumerable<object> GetServices(Type serviceType)
{
foreach (object obj in ObjectFactory.GetAllInstances(serviceType))
{
yield return obj;
}
}
}
but I have now changed to this based on Steve Smith's blog post linked to in Jeremy Miller's blog post:
public class StructureMapDependencyResolver : IDependencyResolver
{
public object GetService(Type serviceType)
{
if (serviceType.IsAbstract || serviceType.IsInterface)
{
return ObjectFactory.TryGetInstance(serviceType);
}
else
{
return ObjectFactory.GetInstance(serviceType);
}
}
public IEnumerable<object> GetServices(Type serviceType)
{
foreach (object obj in ObjectFactory.GetAllInstances(serviceType))
{
yield return obj;
}
}
}
on its own this still doesn't resolve the issue until I remove this configuration expression:
x.For<IControllerFactory>().Use<DefaultControllerFactory>();
According to the documentation TryGetInstance only returns types registered with the container and will return null if none exist. I presume the MVC 3 code relies on this behaviour to indicate that it should use its defaults, hence in my original case I had to register these defaults with my container. Tricky one!

Answer 3

This works for me for both MVC and Web API..
namespace Web.Utilities.DependencyResolvers
{
public class StructureMapResolver : IServiceLocator, IDependencyResolver
{
private readonly IContainer _container;
public StructureMapResolver(IContainer container)
{
if (container == null)
throw new ArgumentNullException("container");
this._container = container;
}
public IDependencyScope BeginScope()
{
return new StructureMapResolver(this._container.GetNestedContainer());
}
public object GetInstance(Type serviceType, string instanceKey)
{
if (string.IsNullOrEmpty(instanceKey))
{
return GetInstance(serviceType);
}
return this._container.GetInstance(serviceType, instanceKey);
}
public T GetInstance<T>()
{
return this._container.GetInstance<T>();
}
public object GetService(Type serviceType)
{
return GetInstance(serviceType);
}
public IEnumerable<object> GetServices(Type serviceType)
{
return this._container.GetAllInstances(serviceType).Cast<object>();
}
public T GetInstance<T>(string instanceKey)
{
return this._container.GetInstance<T>(instanceKey);
}
public object GetInstance(Type serviceType)
{
return serviceType.IsAbstract || serviceType.IsInterface ?
this._container.TryGetInstance(serviceType) : this._container.GetInstance(serviceType);
}
public IEnumerable<T> GetAllInstances<T>()
{
return this._container.GetAllInstances<T>();
}
public IEnumerable<object> GetAllInstances(Type serviceType)
{
return this._container.GetAllInstances(serviceType).Cast<object>();
}
public void Dispose()
{
this._container.Dispose();
}
}
}