创建控制器失败，说明控制器需要一个无参数的公共构造函数

Question

“UserController”类型的创建控制器失败。确保 控制器有一个无参数的公共构造函数

使用 AutoFac，我注册了 UnitOfWork 存储库，如下所示，我还粘贴了控制器代码和堆栈跟踪。请协助。无法理解为什么控制器需要无参数的公共构造函数。

private static IContainer RegisterServices(ContainerBuilder builder)
        {
            //Register your Web API controllers.  
            builder.RegisterApiControllers(Assembly.GetExecutingAssembly());

            builder.RegisterType<UserContext>().As<DbContext>().InstancePerRequest();
            builder.RegisterType<DBFactory>().As<IDBFactory>().InstancePerRequest();
            builder.RegisterType<UnitOfWork>().As<IUnitOfWork>().InstancePerRequest();
            builder.RegisterGeneric(typeof(GenericRepo<>)).As(typeof(IGenericRepo<>)).InstancePerRequest();

            //Set the dependency resolver to be Autofac.  
            Container = builder.Build();

            return Container;
        }  

private readonly IUnitOfWork _unitofwork;
        public UserController(IUnitOfWork uow)
        {
            _unitofwork = uow;
        }
        [HttpGet]
        public IEnumerable<UserDetail> UserData()
        {
            return _unitofwork.userDetail.GetAllUsers();
        }

堆栈跟踪

  at Autofac.Core.Activators.Reflection.ReflectionActivator.ActivateInstance(IComponentContext context, IEnumerable`1 parameters)
       at Autofac.Core.Resolving.InstanceLookup.Activate(IEnumerable`1 parameters)
       at Autofac.Core.Resolving.InstanceLookup.<Execute>b__0()
       at Autofac.Core.Lifetime.LifetimeScope.GetOrCreateAndShare(Guid id, Func`1 creator)
       at Autofac.Core.Resolving.InstanceLookup.Execute()
       at Autofac.Core.Resolving.ResolveOperation.GetOrCreateInstance(ISharingLifetimeScope currentOperationScope, IComponentRegistration registration, IEnumerable`1 parameters)
       at Autofac.Core.Resolving.InstanceLookup.ResolveComponent(IComponentRegistration registration, IEnumerable`1 parameters)
       at Autofac.Core.Activators.Reflection.AutowiringParameter.<>c__DisplayClass2.<CanSupplyValue>b__0()
       at Autofac.Core.Activators.Reflection.ConstructorParameterBinding.Instantiate()
       at Autofac.Core.Activators.Reflection.ReflectionActivator.ActivateInstance(IComponentContext context, IEnumerable`1 parameters)
       at Autofac.Core.Resolving.InstanceLookup.Activate(IEnumerable`1 parameters)
       at Autofac.Core.Resolving.InstanceLookup.Execute()
       at Autofac.Core.Resolving.ResolveOperation.GetOrCreateInstance(ISharingLifetimeScope currentOperationScope, IComponentRegistration registration, IEnumerable`1 parameters)
       at Autofac.Core.Resolving.ResolveOperation.ResolveComponent(IComponentRegistration registration, IEnumerable`1 parameters)
       at Autofac.Core.Resolving.ResolveOperation.Execute(IComponentRegistration registration, IEnumerable`1 parameters)
       at Autofac.Core.Lifetime.LifetimeScope.ResolveComponent(IComponentRegistration registration, IEnumerable`1 parameters)
       at Autofac.ResolutionExtensions.TryResolveService(IComponentContext context, Service service, IEnumerable`1 parameters, Object& instance)
       at Autofac.ResolutionExtensions.ResolveOptionalService(IComponentContext context, Service service, IEnumerable`1 parameters)
       at Autofac.ResolutionExtensions.ResolveOptional(IComponentContext context, Type serviceType, IEnumerable`1 parameters)
       at Autofac.ResolutionExtensions.ResolveOptional(IComponentContext context, Type serviceType)
       at Autofac.Integration.WebApi.AutofacWebApiDependencyScope.GetService(Type serviceType)
       at System.Web.Http.Dispatcher.DefaultHttpControllerActivator.GetInstanceOrActivator(HttpRequestMessage request, Type controllerType, Func`1& activator)
       at System.Web.Http.Dispatcher.DefaultHttpControllerActivator.Create(HttpRequestMessage request, HttpControllerDescriptor controllerDescriptor, Type controllerType)

控制器：

public class UserController : ApiController
{
  private readonly IUnitOfWork _unitofwork;
  public UserController(IUnitOfWork uow)
  {
      _unitofwork = uow;
  }

  [HttpGet]
  public IEnumerable<UserDetail> UserData()
  {
      return _unitofwork.userDetail.GetAllUsers();
  }
}

Answer 1

As stated in the documentation, you need set the dependency resolver:

构建容器后，将其传递给 AutofacWebApiDependencyResolver 类的新实例。将新的解析器附加到您的 HttpConfiguration.DependencyResolver 以让 Web API 知道它应该使用 AutofacWebApiDependencyResolver 定位服务。这是 Autofac 对 IDependencyResolver 接口的实现。

var container = builder.Build();
config.DependencyResolver = new AutofacWebApiDependencyResolver(container);

我可以告诉你没有这样做，因为堆栈跟踪明确说明了它用于创建控制器的解析器：

System.Web.Http.Dispatcher.DefaultHttpControllerActivator.GetInstanceOrActivator(HttpRequestMessage request, Type controllerType, Func`1& activator)

Answer 2

问题是由于 IDbFactory 设置错误。