我正在创建一个带有 MEF 和 Unity 集成的 Microsft MVC4 应用程序来处理插件架构(其他 MVC4 项目)及其依赖项。但是,当我尝试选择包含 Unity 依赖项的 MEF 导入控制器时收到错误消息。这是错误:
1) 无法创建类型为“X”的实例,因为无法选择构造函数进行构造。确保该类型具有默认构造函数,或者具有标有“System.ComponentModel.Composition.ImportingConstructorAttribute”的单个构造函数。
主 MVC4 应用 MEF + Unity 集成代码:
// Create MEF catalog from plugin directory.
var aggregateCatalog = new AggregateCatalog(new DirectoryCatalog(HostingEnvironment.MapPath("~/bin"), "*.dll"));
// Setup Unity container based on catalog.
var unityContainer = new UnityContainer();
unityContainer.RegisterCatalog(aggregateCatalog);
// Register dependancy.
unityContainer.RegisterType<ISystemService, SystemService>();
// Compose the MEF container.
CompositionContainer container = new CompositionContainer(aggregateCatalog, true);
container.ComposeParts(aggregateCatalog.Catalogs);
// Register the controller factory that will handle requests.
ControllerBuilder.Current.SetControllerFactory(new MefControllerFactory(container));
var dependencyResolver = System.Web.Http.GlobalConfiguration.Configuration.DependencyResolver;
System.Web.Http.GlobalConfiguration.Configuration.DependencyResolver = new MefDependencyResolver(container);
从 MEF 中选择合适控制器的 CreateController 方法
// Get all the exported controllers.
var exports = _container.GetExports<IController, INameMetadata>();
// Select controller based off meta data.
var controller = exports.Where(e => e.Metadata.Name.ToLower().Equals(controllerName.ToLower())
&& e.Metadata.Module.ToLower().Equals(module.ToLower()))
.Select(e => e.Value).FirstOrDefault();
我要导入的控制器的设置。它是抽象基类的子类。
基类。
public abstract class WidgetController : Controller
{
[Dependency]
public ISystemService _systemService { get; set; }
[ImportingConstructor]
public WidgetController(ISystemService systemService)
{
_systemService = systemService;
}
}
儿童班。
[InheritedExport(typeof(IController))]
[ExportMetadata("Module", "TheComponent")]
[ExportMetadata("Name", "TheName")]
[PartCreationPolicy(CreationPolicy.NonShared)]
public class WidgetXController : WidgetController
{
public WidgetXController (ISystemService systemService)
: base(systemService)
{
}
}
使用这种结构,WidgetXController 可作为 CreateController 方法中的导出使用。但是,当尝试在 LINQ 查询中选择它时,我收到上述错误消息。我尝试将 [ImportingConstructor] 属性添加到子类,但这会导致控制器进入导出列表。我认为 MEF + Unity 集成中的某些设置不正确......
是否有人对 MEF + Unity 集成功能如何帮助解决我看到的错误有任何见解?