1

我很难理解 Mef 以及导入和导出的工作原理。我的项目结构如下。

Projects:
MefMVPApp (Main MVC 4 app)
MefMVCFramework.Common(Interfaces shared between the projects)
MefMVCDemo.Plugins.OrderStatus (pluggable area.)
MefMVCDemo.Plugins.Data (Repository for OrderStatus)
OrderStatus.Models(domain models shared between the projects)

主 Mvc 应用程序的目标是通过 mef 托管可插入区域。

OrderStatus 区域有一个名为 OrderStatusController 的控制器，并使用 Export Attribute 和 ImportingConstructor 进行装饰。

[Export(typeof(IController))]
        [ExportMetadata("controllerName", "OrderStatus")]
        [PartCreationPolicy(CreationPolicy.NonShared)] 
        public class OrderStatusController : Controller
        {
            private readonly IRepository<OrderStatusApp.OrderStatusResponse>_repository ;
            [ImportingConstructor]
            public OrderStatusController(IRepository<OrderStatusApp.OrderStatusResponse> oRepository)
            {
                _repository = oRepository;
            }
            public ActionResult Index()
            {
                var model = _repository.GetAll();
                return View();
            } 
    }

IRepository 是 MefMVCFramework.Common 程序集中的一个类，将用于通用 CRUD 操作。

public interface IRepository<T> where T : class
            {
               IEnumerable<T> GetAll();
               T GetById(int id);
               void Add(T entity);
               int SaveOrUpdate(T entity);
                bool Delete(T entity);
                bool Delete(int id); 
            }

MefMVCDemo.Plugins.Data 程序集包含一个名为 OrderManagementRepository 的类，它是通用存储库的固有属性，并标有导出属性。

[Export(typeof(IRepository<OrderStatusApp.OrderStatusResponse>))]
            [PartCreationPolicy(CreationPolicy.NonShared)] 
                public class OrderManagementRepository  : IRepository<OrderStatusApp.OrderStatusResponse>
                {
                    private readonly JsonServiceClient _client;

                    public OrderManagementRepository()
                    {
                        _client = new JsonServiceClient("http://localhost:52266");
                    }
                    public IEnumerable<OrderStatusApp.OrderStatusResponse> GetAll()
                    {

                        throw new NotImplementedException("Can not get all");
                    }
                    public OrderStatusApp.OrderStatusResponse GetById(int id)
                    {
                        throw new NotImplementedException();
                    }
                    public void Add(OrderStatusApp.OrderStatusResponse entity)
                    {
                        throw new NotImplementedException();
                    }
                    public int SaveOrUpdate(OrderStatusApp.OrderStatusResponse entity)
                    {
                        throw new NotImplementedException();
                    }
                    public bool Delete(OrderStatusApp.OrderStatusResponse entity)
                    {
                        throw new NotImplementedException();
                    }
                    public bool Delete(int id)
                    {
                        throw new NotImplementedException();
                    }
                }

使用 Mefx 工具，我可以看到我的零件并且没有拒绝。

mefx /dir:C:\
Source.PreBranch.Keep\Prototypes\Projects\MefDemoApp\mefMVC4App\bin /parts
MefMVCDemo.Plugins.Data.OrderManagementRepository
mefMVCDemo.Plugins.OrderStatus.Controllers.OrderStatusController
MefMVCDemo.Plugins.OrderStatus.Verbs.OrderStatusVerb

我可以看到我的导入。

mefx /dir:C:\
Source.PreBranch.Keep\Prototypes\Projects\MefDemoApp\mefMVC4App\bin /imports
MefMVCFramework.Common.IRepository(OrderStatus.Models.OrderStatusApp+OrderStatus
Response)
MefMVCFramework.Common.IRepository(OrderStatus.Models.OrderStatusApp+OrderStatus
Response)

现在，当使用 /orderstatus uri 浏览我的主 mvc 站点时，我收到以下错误：没有为此对象定义无参数构造函数。

将默认构造函数添加到不带重载的 OrderStatusController 似乎不起作用。

我想问题是我做错了什么？为什么我在构造函数中的接口最终都是空的，为什么会出现关于“没有为此对象定义无参数构造函数”的 mvc 错误。

4

2 回答 2

1

MVC 中的默认控制器工厂尝试使用无参数构造函数创建控制器。如果你想改变这种行为，那么你需要创建你自己的自定义控制器工厂。

这是在控制器上使用导入/导出的 ControllerFactory示例

我正在使用 MEF 将一些部件导入我的应用程序，但我的控制器没有导入/导出，所以我创建了以下控制器工厂

public class ControllerFactory : IControllerFactory
{
    private readonly CompositionContainer _container;
    private IControllerFactory _innerFactory;

/// <summary>
/// Constructor used to create the factory
/// </summary>
/// <param name="container">MEF Container that will be used for importing</param>
public ControllerFactory(CompositionContainer container)
{
    _container = container;
    _innerFactory = new DefaultControllerFactory();
}

/// <summary>
/// Method used for create the controller based on the provided name. It calls the
/// constructor of the controller passing the MEF container
/// </summary>
/// <param name="requestContext">Context of the request</param>
/// <param name="controllerName">Name of the controller provided in the route</param>
/// <returns>The controller instance</returns>
public IController CreateController(System.Web.Routing.RequestContext requestContext, string controllerName)
{
    Type controllerType = FindControllerByName(controllerName);

    var args = new object[] { this._container };
    var controller = (IController)Activator.CreateInstance(controllerType, args);

    return controller;
}

/// <summary>
/// This methods looks into the current Assembly for the Controller type
/// </summary>
/// <param name="name">The controller name provided in the route</param>
/// <returns>The controller type</returns>
private static Type FindControllerByName(string name){
    var a = Assembly.GetAssembly(typeof(ControllerFactory));
    var types = a.GetTypes();
    Type type = types.Where(t => t.Name == String.Format("{0}Controller", name)).FirstOrDefault();              

    return type;
}


public System.Web.SessionState.SessionStateBehavior GetControllerSessionBehavior(System.Web.Routing.RequestContext requestContext, string controllerName)
{
    return System.Web.SessionState.SessionStateBehavior.Default;
}

public void ReleaseController(IController controller)
{
    var disposableController = controller as IDisposable;
    if (disposableController != null)
    {
        disposableController.Dispose();
    }
}

}

于 2013-04-09T20:57:32.843 回答
1

感谢 pollirrata 为我指明了正确的方向。

我不得不改变一些事情来让它工作。

1.) 我在 MefMVCFramework.Common 项目中添加了一个名为 INameMetadata 的接口。

public interface INameMetadata
{
    string Name { get; }
}

2.) 将我的控制器导出上的我的 ExportMetadata 标签修改为 Name、OrderStatus。

 [Export(typeof(IController))]
[ExportMetadata("Name", "OrderStatus")]
[PartCreationPolicy(CreationPolicy.NonShared)] 
public class OrderStatusController : Controller
{
    private IRepository<OrderStatusApp.OrderStatusResponse> _repository;

    [ImportingConstructor]
    public OrderStatusController(IRepository<OrderStatusApp.OrderStatusResponse> oRepository)
    {
        _repository = oRepository;

    }

    public ActionResult Index()
    {
        var model = _repository.GetById(47985);
        return View(model);
    } 
}

3.) 创建 MefControllerFactory（基于 pollirrata 发布但修改为查找元数据的内容）

 public class MefControllerFactory : IControllerFactory
{
    private string _pluginPath;
    private readonly DirectoryCatalog _catalog;
    private readonly CompositionContainer _container;
    private DefaultControllerFactory _defaultControllerFactory;

    public MefControllerFactory(string pluginPath)
    {
        _pluginPath = pluginPath;
        _catalog = new DirectoryCatalog(pluginPath);
        _container = new CompositionContainer(_catalog);
        _defaultControllerFactory = new DefaultControllerFactory();
    }

    public MefControllerFactory(CompositionContainer compositionContainer)
    {

        _container = compositionContainer;
        _defaultControllerFactory = new DefaultControllerFactory();
    }
    #region IControllerFactory Members
    public IController CreateController(System.Web.Routing.RequestContext requestContext, string controllerName)
    {
        //IController controller = null;
        var controller = _container.GetExports<IController,INameMetadata>()
            .Where(e=>e.Metadata.Name.Equals(controllerName))
            .Select(e=>e.Value).FirstOrDefault();

        if (controller == null)
        {
            throw new HttpException(404, "Not found");
        }

        return controller;

    }
    public void ReleaseController(IController controller)
    {
       var disposable = controller as IDisposable;
        if (disposable != null)
        {
            disposable.Dispose();
        }
    }
    #endregion


    public SessionStateBehavior GetControllerSessionBehavior(System.Web.Routing.RequestContext requestContext, string controllerName)
    {
        return SessionStateBehavior.Default;
    }
}

4.) 我在 Main MVC 应用程序中创建了一个名为 MefConfig 的类并将其移至 App_Start 目录。

public static class MefConfig
{
    public static void RegisterMef()
    {
        //var builder = new RegistrationBuilder();
        //builder.ForTypesDerivedFrom<IRepository<OrderStatusApp.OrderStatusResponse>>().Export<IRepository<IRepository<OrderStatusApp.OrderStatusResponse>>>();

        var directoryCatalog = new DirectoryCatalog(HostingEnvironment.MapPath("~/bin"), "*.dll");

        var container = new CompositionContainer(directoryCatalog, true);
        ControllerBuilder.Current.SetControllerFactory(new MefControllerFactory(container));

        //Working
        //ControllerBuilder.Current.SetControllerFactory(new MefControllerFactory(HostingEnvironment.MapPath("~/bin")));

        // Install MEF dependency resolver for MVC
        var resolver = new MefDependencyResolver(container);
        DependencyResolver.SetResolver(resolver);
        // Install MEF dependency resolver for Web API
        GlobalConfiguration.Configuration.DependencyResolver = resolver;
        var d = container.GetExportedValues<IRepository<OrderStatusApp.OrderStatusResponse>>();
        //Mefx.
        try
        {
            //var ci = new CompositionInfo(aggregateCatalog, container);
            var ci = new CompositionInfo(directoryCatalog, container);
            var partDef = ci.GetPartDefinitionInfo(typeof(IRepository<OrderStatusApp.OrderStatusResponse>));

            //var possibleCauses = partDef.FindPossibleRootCauses();
            var stringWriter = new StringWriter();
            CompositionInfoTextFormatter.Write(ci, stringWriter);
            var compStatString = stringWriter.ToString();
        }
        catch
        {

        }
        MvcApplication.ActionVerbs = container.GetExports<IActionVerb, IActionVerbMetadata>();
    }
}

5.) 从 global.asax 加载 Mefconfig。

 protected void Application_Start()
    {
        AreaRegistration.RegisterAllAreas();
        //Register Mef 
        MefConfig.RegisterMef();

        WebApiConfig.Register(GlobalConfiguration.Configuration);
        FilterConfig.RegisterGlobalFilters(GlobalFilters.Filters);
        RouteConfig.RegisterRoutes(RouteTable.Routes);
        BundleConfig.RegisterBundles(BundleTable.Bundles);

    }
于 2013-04-10T18:47:24.920 回答