How to integrate MEF with ASP.NET MVC 4 and ASP.NET Web API
The solution is to implement System.Web.Mvc.IDependencyResolver and System.Web.Http.Dependencies.IDependencyResolver and register your implementation with ASP.NET MVC and ASP.NET Web API respectively, in your Application_Start
method.
In this example we'll create a class MefConfig
, which implements a method RegisterMef
that gets called from Application_Start
in order to install our dependency resolver. The class MefDependencyResolver
implements both System.Web.Mvc.IDependencyResolver
and System.Web.Http.Dependencies.IDependencyResolver
and, as such, handles dependency resolution duties for both MVC and Web API.
Application_Start, Put This in Your Global.asax.cs:
public class WebApiApplication : System.Web.HttpApplication
{
protected void Application_Start()
{
[...]
MefConfig.RegisterMef();
}
}
MefDependencyResolver and MefConfig:
/// <summary>
/// Resolve dependencies for MVC / Web API using MEF.
/// </summary>
public class MefDependencyResolver : System.Web.Http.Dependencies.IDependencyResolver, System.Web.Mvc.IDependencyResolver
{
private readonly CompositionContainer _container;
public MefDependencyResolver(CompositionContainer container)
{
_container = container;
}
public IDependencyScope BeginScope()
{
return this;
}
/// <summary>
/// Called to request a service implementation.
///
/// Here we call upon MEF to instantiate implementations of dependencies.
/// </summary>
/// <param name="serviceType">Type of service requested.</param>
/// <returns>Service implementation or null.</returns>
public object GetService(Type serviceType)
{
if (serviceType == null)
throw new ArgumentNullException("serviceType");
var name = AttributedModelServices.GetContractName(serviceType);
var export = _container.GetExportedValueOrDefault<object>(name);
return export;
}
/// <summary>
/// Called to request service implementations.
///
/// Here we call upon MEF to instantiate implementations of dependencies.
/// </summary>
/// <param name="serviceType">Type of service requested.</param>
/// <returns>Service implementations.</returns>
public IEnumerable<object> GetServices(Type serviceType)
{
if (serviceType == null)
throw new ArgumentNullException("serviceType");
var exports = _container.GetExportedValues<object>(AttributedModelServices.GetContractName(serviceType));
return exports;
}
public void Dispose()
{
}
}
public static class MefConfig
{
public static void RegisterMef()
{
var asmCatalog = new AssemblyCatalog(Assembly.GetExecutingAssembly());
var container = new CompositionContainer(asmCatalog);
var resolver = new MefDependencyResolver(container);
// Install MEF dependency resolver for MVC
DependencyResolver.SetResolver(resolver);
// Install MEF dependency resolver for Web API
System.Web.Http.GlobalConfiguration.Configuration.DependencyResolver = resolver;
}
}
@aknuds1 answer is the best I've seen so far for integrating MEF into the DependencyResolver. I was able to extend it to use the convention-based composition in MEF2 fairly easily. The MefConfig class is all that needed to change and then not by much.
/// <summary>
/// Responsible for configuring MEF for the application.
/// </summary>
public static class MefConfig
{
/// <summary>
/// Registers MEF conventions and exports.
/// </summary>
public static void RegisterMef()
{
// Register MVC/API conventions
var registrationBuilder = new RegistrationBuilder();
registrationBuilder.ForTypesDerivedFrom<Controller>().SetCreationPolicy(CreationPolicy.NonShared).Export();
registrationBuilder.ForTypesDerivedFrom<ApiController>().SetCreationPolicy(CreationPolicy.NonShared).Export();
var assemblyCatalog = new AssemblyCatalog(Assembly.GetExecutingAssembly(), registrationBuilder);
var aggregateCatalog = new AggregateCatalog(assemblyCatalog);
var container = new CompositionContainer(aggregateCatalog);
var resolver = new MefDependencyResolver(container);
// Install MEF dependency resolver for MVC
DependencyResolver.SetResolver(resolver);
// Install MEF dependency resolver for Web API
GlobalConfiguration.Configuration.DependencyResolver = resolver;
}
}