asp.net - 简单注入(inject)器 - 解析 MVC Controller 时没有为此对象定义无参数构造函数

Question

我有一个新的 MVC Web 项目，我在其中使用 MVC 和 Web API。我在全局文件中使用以下代码设置了 Simple Injector(来自 NuGet 的 2.5.2 版)

// Register Injectors
SimpleInjectorConfig.Register();

在我的 SimpleInjectorConfig.cs 文件中，我有

public class SimpleInjectorConfig
{
    public static void Register() {
        // Create the container as usual.
        Container container = new Container();

        // services
        container.Register<IService, MyService>();

        // data
        container.Register<IRepository, MyRepository>();

        // Register your types, for instance using the RegisterWebApiRequest
        // extension from the integration package:
        container.RegisterMvcControllers(
            System.Reflection.Assembly.GetExecutingAssembly());

        container.RegisterMvcAttributeFilterProvider();

        // This is an extension method from the integration package.
        container.RegisterWebApiControllers(GlobalConfiguration.Configuration);

        // verify its all ok
        container.Verify();

        // add dependency
        GlobalConfiguration.Configuration.DependencyResolver = 
            new SimpleInjectorWebApiDependencyResolver(container);
    }
}

现在我有 2 个 Controller ，1 个是 Web API Controller ，1 个是普通的 MVC Controller 。
我的 Web API Controller 工作正常，看起来像这样

public class MyApiController : ApiController
{
    private IService _service;

    public MyApiController(IService service)
    {
        _service = service;
    }

    public IHttpActionResult Get(int id)
    {
        // I get my entity here and return it
        EntityObject myEntity = _service.Get(id);
        return Ok(myEntity);
    }
}

正如我所说，上面的代码工作正常，我可以执行 URL 并返回我所期望的。
现在我有了我的 MVC Controller ，它看起来与上面的非常相似，这里是

public class MyController : Controller
{
    private IService _service;

    public MyController(IService service)
    {
        _service = service;
    }

    public ActionResult Index()
    {
        return Search();
    }

    public ActionResult Search()
    {
        return View();
    }
}

现在我完全不明白为什么我不断收到以下错误。我无法添加公共(public)构造函数，因为这会导致 Simple Injector 出错。

System.MissingMethodException: No parameterless constructor defined for this object.

   System.RuntimeTypeHandle.CreateInstance(RuntimeType type, Boolean publicOnly, Boolean noCheck, Boolean& canBeCached, RuntimeMethodHandleInternal& ctor, Boolean& bNeedSecurityCheck) +0
   System.RuntimeType.CreateInstanceSlow(Boolean publicOnly, Boolean skipCheckThis, Boolean fillCache, StackCrawlMark& stackMark) +113
   System.RuntimeType.CreateInstanceDefaultCtor(Boolean publicOnly, Boolean skipCheckThis, Boolean fillCache, StackCrawlMark& stackMark) +232
   System.Activator.CreateInstance(Type type, Boolean nonPublic) +83
   System.Activator.CreateInstance(Type type) +66
   System.Web.Mvc.DefaultControllerActivator.Create(RequestContext requestContext, Type controllerType) +110

[InvalidOperationException: An error occurred when trying to create a controller of type 'my.project.Web.Controllers.MyController'. Make sure that the controller has a parameterless public constructor.]
   System.Web.Mvc.DefaultControllerActivator.Create(RequestContext requestContext, Type controllerType) +247
   System.Web.Mvc.DefaultControllerFactory.GetControllerInstance(RequestContext requestContext, Type controllerType) +438
   System.Web.Mvc.DefaultControllerFactory.CreateController(RequestContext requestContext, String controllerName) +257
   System.Web.Mvc.MvcHandler.ProcessRequestInit(HttpContextBase httpContext, IController& controller, IControllerFactory& factory) +328
   System.Web.Mvc.MvcHandler.BeginProcessRequest(HttpContextBase httpContext, AsyncCallback callback, Object state) +157
   System.Web.Mvc.MvcHandler.BeginProcessRequest(HttpContext httpContext, AsyncCallback callback, Object state) +88
   System.Web.Mvc.MvcHandler.System.Web.IHttpAsyncHandler.BeginProcessRequest(HttpContext context, AsyncCallback cb, Object extraData) +50
   System.Web.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +301
   System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +155

如果有人能指出我正确的方向，那就太好了。

Answer 1

出现此错误的原因是您缺少以下注册(如 MVC integration guide 中所述):

DependencyResolver.SetResolver(new SimpleInjectorDependencyResolver(container));

MVC 和 Web API 都有自己的解析依赖的抽象(都称为“依赖解析器”)。由于您没有为 MVC 设置解析器，因此 MVC 使用默认解析机制来创建 MVC Controller ，但这需要 Controller 具有默认构造函数。

调用DependencyResolver.SetResolver将解决问题。