在ServiceStack服務中使用MEF容器

1.ServiceStack服務擁有自身的容器—Funq.Container

當我們使用介面註入的方式調用底層方法時，我們需要在AppHost中重寫Configure(Funq.Container container)方法，在方法中添加container.RegisterAutoWiredAs<T, TAs>()配置，才能在服務中使用構造函數註入方式調用介面。代碼示例如下：

AppHost.cs:

public class AppHost : AppHostBase
    {
        public AppHost() //Tell ServiceStack the name and where to find your web services
            : base("OAuth2 Demo Resource Server", typeof(UserService).Assembly) { }

        public override void Configure(Funq.Container container)
        {
            //Set JSON web services to return idiomatic JSON camelCase properties
            ServiceStack.Text.JsConfig.EmitCamelCaseNames = true;

            //Configure User Defined REST Paths
            Routes
              .Add<Users>("/users")
              .Add<Users>("/users/{Username}");

            //Register all your dependencies

            container.RegisterAutoWiredAs<FakeUserStore, IUserStore>();
        }
    }

UserService.cs

public class UserService : Service {
        private readonly IUserStore userStore;

        public UserService(IUserStore userStore) {
            this.userStore = userStore;
        }

        public User Any(Users users) {
            if (HttpContext.Current.User.Identity.Name != users.Username) {
                throw (new UnauthorizedAccessException(String.Format("Your access token doesn't grant access to information for the user named {0}", users.Username)));
            }
            return (userStore.GetUser(users.Username));
        }
    }

缺點：每個介面都需要添加container.RegisterAutoWiredAs<T, TAs>()配置來實例化介面，太過繁瑣。

2.ServiceStack服務調用MEF組合容器—CompositionContainer

MEF 提供一種通過“組合”隱式發現組件的方法。 MEF 組件（稱為“部件-Part”）。部件以聲明方式同時指定其依賴項（稱為“導入-Import”）及其提供的功能（稱為“導出-Export”）。MEF原理上很簡單，找出有共同介面的導入、導出。然後找到把導出的實例化，賦給導入。說到底MEF就是找到合適的類實例化，把它交給導入。

當我們在ServiceStack中調用MEF容器時，我們就可以使用組合容器通過目錄搜索組件的定義。步驟如下

2.1 自定義一個IContainerAdapter適配器

using ServiceStack.Configuration;
using System.ComponentModel.Composition.Hosting;

namespace OAuthStack.DataServer.Infrastructure
{
    internal class MefIOCAdapter : IContainerAdapter
    {
        private readonly CompositionContainer _container;

        internal MefIOCAdapter(CompositionContainer container)
        {
            _container = container;
        }

        public T TryResolve<T>()
        {
            return _container.GetExportedValueOrDefault<T>();
        }

        public T Resolve<T>()
        {
            return _container.GetExportedValue<T>();
        }
    }
}

2.在AppHost中重寫Configure(Funq.Container container)方法，註冊MefIOCAdapter適配器

using OAuthStack.DataServer.Services;
using ServiceStack.ServiceInterface.Cors;
using ServiceStack.WebHost.Endpoints;
using System.ComponentModel.Composition.Hosting;
using System.Web.Hosting;

namespace OAuthStack.DataServer.Infrastructure
{
    public class AppHost : AppHostBase
    {
        public AppHost()
            : base("OAuth2 Demo Resource Server", typeof(EquipmentService).Assembly) { }

        public override void Configure(Funq.Container container)
        {
            //Set JSON web services to return idiomatic JSON camelCase properties
            ServiceStack.Text.JsConfig.EmitCamelCaseNames = true;
            //配置跨域
            Plugins.Add(new CorsFeature());
            //註冊用戶認證證書
            

            string directoryName = System.AppDomain.CurrentDomain.BaseDirectory.ToString() + "bin\\";
            AggregateCatalog aggregateCatalog = new AggregateCatalog();
            if (directoryName != null)
            {
                //DirectoryCatalog 在指定的目錄發現部件。
                aggregateCatalog.Catalogs.Add(new DirectoryCatalog(directoryName, "Service*"));
                aggregateCatalog.Catalogs.Add(new DirectoryCatalog(directoryName, "Persistance.dll"));
            }
            CompositionContainer _mefContainer = new CompositionContainer(aggregateCatalog);
            container.Adapter = new MefIOCAdapter(_mefContainer);
        }
    }
}

Service.cs

 public class TService : Service
    {
        private readonly ITDao _tDao;

        [ImportingConstructor]
        public TService(ITDao tDao)
        {
            _tDao = tDao;
        }
}

優點：無需逐個配置介面實例化，充分利用MEF導入—導出的優點。