如何在同一个项目中将托管扩展性框架（MEF）与 ASP.NET MVC 4和 ASP.NET Web API集成？
考虑一个示例应用程序，其中包含 MVC 控制器HomeController和 Web API 控制器ContactController。两者都有一个类型 IContactRepository 的属性，它们依靠 MEF 来解析。问题是如何将 MEF 插入 MVC 和 Web API，以便通过 MEF 创建实例。
主控制器：
/// <summary>
/// Home controller. Instruct MEF to create one instance of this class per importer,
/// since this is what MVC expects.
/// </summary>
[Export]
[PartCreationPolicy(CreationPolicy.NonShared)]
public class HomeController : Controller
{
[Import]
private IContactRepository _contactRepository = null;
public ActionResult Index()
{
return View(_contactRepository.GetAllContacts());
}
}
联系人控制器：
/// <summary>
/// Contact API controller. Instruct MEF to create one instance of this class per importer,
/// since this is what Web API expects.
/// </summary>
[Export]
[PartCreationPolicy(CreationPolicy.NonShared)]
public class ContactController : ApiController
{
[Import]
private IContactRepository _contactRepo = null;
public Contact[] Get()
{
return _contactRepo.GetAllContacts();
}
}
IContactRepository 和 ContactRepository：
public interface IContactRepository
{
Contact[] GetAllContacts();
}
[Export(typeof(IContactRepository))]
public class ContactRepository : IContactRepository
{
public Contact[] GetAllContacts()
{
return new Contact[] {
new Contact { Id = 1, Name = "Glenn Beck"},
new Contact { Id = 2, Name = "Bill O'Riley"}
};
}
}
联系：
public class Contact
{
public int Id { get; set; }
public string Name { get; set; }
}
解决方案是实现 System.Web.Mvc.IDependencyResolver 和 System.Web.Http.Dependencies.IDependencyResolver，并在 Application_Start 方法中分别向 ASP.NET MVC 和 ASP.NET Web API 注册实现。
在此示例中，我们将创建一个类MefConfig ，它实现从Application_Start调用的方法RegisterMef以安装我们的依赖项解析器。类MefDependencyResolver实现System.Web.Mvc.IDependencyResolver和System.Web.Http.Dependencies.IDependencyResolver，因此处理 MVC 和 Web API 的依赖项解析职责。
Application_Start，把它放在你的global.asax.cs：
public class WebApiApplication : System.Web.HttpApplication
{
protected void Application_Start()
{
[...]
MefConfig.RegisterMef();
}
}
MefDependencyResolver 和 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答案是我迄今为止见过的将 MEF 集成到依赖项解析器中的最佳答案。我能够相当轻松地扩展它以使用MEF2中基于约定的合成。MefConfig 类是所有需要更改的，然后不会更改太多。
/// <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;
}
}
你可以看看这个 http://kennytordeur.blogspot.be/2012/08/mef-in-aspnet-mvc-4-and-webapi.html。它解释了如何在 Asp.net MVC 4/Web Api项目中使用MEF。还存在基于此代码的 Nuget 包。这样您就可以非常轻松快速地对其进行测试。
@aknuds1的解决方案有效，但在每次 API 调用时都会泄漏内存。我已经修改了他的解决方案以修复泄漏。
public class MefDependencyResolver : System.Web.Http.Dependencies.IDependencyResolver, System.Web.Mvc.IDependencyResolver
{
private readonly CompositionContainer container;
private readonly List<Lazy<object, object>> exports = new List<Lazy<object, object>>();
private readonly object syncRoot = new object();
public MefDependencyResolver(CompositionContainer container)
{
this.container = container;
}
public IDependencyScope BeginScope()
{
return new MefDependencyResolver(container);
}
/// <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(nameof(serviceType));
var serviceExport = container.GetExports(serviceType, null, null).FirstOrDefault();
if (serviceExport == null) return null;
lock (this.syncRoot)
{
exports.Add(serviceExport);
}
return serviceExport.Value;
}
/// <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(nameof(serviceType));
var serviceExports = container.GetExports(serviceType, null, null);
if (!serviceExports.Any()) return Enumerable.Empty<object>();
lock (this.syncRoot)
{
exports.AddRange(serviceExports);
}
return serviceExports.Select(x => x.Value);
}
public void Dispose()
{
lock (this.syncRoot)
{
foreach (var e in exports)
{
this.container.ReleaseExport(e);
}
exports.Clear();
}
}
}
这是我在 MVC4 项目中使用的一种更简单的方法。
public static class MefConfig
{
public static CompositionContainer MefContainer = null;
public static void Initialise()
{
AggregateCatalog cat = new AggregateCatalog();
cat.Catalogs.Add(new AssemblyCatalog(Assembly.GetExecutingAssembly()));
MefContainer = new CompositionContainer(cat);
}
}
public class MefFilterAttribute : ActionFilterAttribute
{
public override void OnActionExecuting(ActionExecutingContext filterContext)
{
MefConfig.MefContainer.ComposeParts(filterContext.Controller);
}
}
在Application_Start运行MefConfig.Initialise（）并在FilterConfig.RegisterGlobalFilters（GlobalFilterCollection过滤器）中放置过滤器。Add（new Filters.MefFilterAttribute（））;
我遵循了@akanuds1的回答，但我也必须将控制器工厂更改为：
public class MefControllerFactory : DefaultControllerFactory
{
private readonly CompositionContainer compositionContainer;
public MefControllerFactory(CompositionContainer compositionContainer)
{
this.compositionContainer = compositionContainer;
}
protected override IController GetControllerInstance(System.Web.Routing.RequestContext requestContext, Type controllerType)
{
var export = compositionContainer.GetExports(controllerType, null, null).SingleOrDefault();
IController result;
if (null != export)
{
result = export.Value as IController;
}
else
{
result = base.GetControllerInstance(requestContext, controllerType);
compositionContainer.ComposeParts(result);
}
return result;
}
}
Glogal.asax.cs
protected void Application_Start()
{
...
var container = MefConfig.Register();
ControllerBuilder.Current.SetControllerFactory(new MefControllerFactory(container));
}