Autofac與Web API 2 - 無參數構造函數錯誤

Question

我想在我的Web API 2項目上安裝Autofac。我以前只用過它幾次。我使用的Nuget安裝了兩個Autofac和Autofac.WebApi2。 然後在我啓動類我這樣做：

public partial class Startup 
{ 
    public void Configuration(IAppBuilder app) 
    { 

     // Get our http configuration 
     var config = new HttpConfiguration(); 

     // Register the Autofac middleware FIRST. This also adds 
     // Autofac-injected middleware registered with the container. 
     var container = ConfigureInversionOfControl(app, config); 

     // Register all areas 
     AreaRegistration.RegisterAllAreas(); 
     GlobalConfiguration.Configure(WebApiConfig.Register); 

     // Use our web api 
     app.UseWebApi(config); 
    } 

    /// <summary> 
    /// Configures Autofac DI/IoC 
    /// </summary> 
    /// <param name="app"></param> 
    /// <param name="config"></param> 
    private IContainer ConfigureInversionOfControl(IAppBuilder app, HttpConfiguration config) 
    { 

     // Create our container 
     var builder = new ContainerBuilder(); 

     // You can register controllers all at once using assembly scanning... 
     builder.RegisterApiControllers(Assembly.GetExecutingAssembly()); 

     // Register our module 
     builder.RegisterModule(new AutofacModule()); 

     // Build 
     var container = builder.Build(); 

     // Lets Web API know it should locate services using the AutofacWebApiDependencyResolver 
     config.DependencyResolver = new AutofacWebApiDependencyResolver(container); 

     // Return our container 
     return container; 
    } 
} 

我創建看起來像這樣的模塊：

public class AutofacModule : Module 
{ 
    protected override void Load(ContainerBuilder builder) 
    { 

     // Create our Singletons 
     builder.RegisterType<DatabaseContext>().As<DbContext>().InstancePerRequest(); 

     // Create our Services 
     builder.RegisterType<UnitOfWork>().As<IUnitOfWork>().InstancePerRequest(); 
     builder.RegisterType<AnswerService>().As<IAnswerService>().InstancePerRequest(); 
     builder.RegisterType<CategoryService>().As<ICategoryService>().InstancePerRequest(); 
     builder.RegisterType<FeedService>().As<IFeedService>().InstancePerRequest(); 
     builder.RegisterType<FilterService>().As<IFilterService>().InstancePerRequest(); 
     builder.RegisterType<QuestionGroupService>().As<IQuestionGroupService>().InstancePerRequest(); 
     builder.RegisterType<StateService>().As<IStateService>().InstancePerRequest(); 

     // Create our providers 
     //builder.RegisterType<AnswerProvider>().As<IAnswerProvider>().InstancePerLifetimeScope(); 
     builder.RegisterType<CategoryProvider>().As<ICategoryProvider>().InstancePerRequest(); 
     builder.RegisterType<FeedProvider>().As<IFeedProvider>().InstancePerRequest(); 
     builder.RegisterType<FilterProvider>().As<IFilterProvider>().InstancePerRequest(); 
     builder.RegisterType<QuestionGroupProvider>().As<IQuestionGroupProvider>().InstancePerRequest(); 
     builder.RegisterType<StateProvider>().As<IStateProvider>().InstancePerRequest(); 
    } 
} 

而且我加了一個供應商作爲一個參數爲我這樣的API構造：

// Readonly properties 
private readonly ICategoryProvider _provider; 

/// <summary> 
/// Default constructor 
/// </summary> 
public CategoriesController(ICategoryProvider provider) 
{ 
    _provider = provider; 
} 

但是，當我嘗試調用API（使用郵遞員）時，出現此錯誤：

{ 
    "message": "An error has occurred.", 
    "exceptionMessage": "An error occurred when trying to create a controller of type 'CategoriesController'. Make sure that the controller has a parameterless public constructor.", 
    "exceptionType": "System.InvalidOperationException", 
    "stackTrace": " at System.Web.Http.Dispatcher.DefaultHttpControllerActivator.Create(HttpRequestMessage request, HttpControllerDescriptor controllerDescriptor, Type controllerType)\r\n at System.Web.Http.Controllers.HttpControllerDescriptor.CreateController(HttpRequestMessage request)\r\n at System.Web.Http.Dispatcher.HttpControllerDispatcher.<SendAsync>d__1.MoveNext()", 
    "innerException": { 
     "message": "An error has occurred.", 
     "exceptionMessage": "Type 'Piiick.Api.Controllers.CategoriesController' does not have a default constructor", 
     "exceptionType": "System.ArgumentException", 
     "stackTrace": " at System.Linq.Expressions.Expression.New(Type type)\r\n at System.Web.Http.Internal.TypeActivator.Create[TBase](Type instanceType)\r\n at System.Web.Http.Dispatcher.DefaultHttpControllerActivator.GetInstanceOrActivator(HttpRequestMessage request, Type controllerType, Func`1& activator)\r\n at System.Web.Http.Dispatcher.DefaultHttpControllerActivator.Create(HttpRequestMessage request, HttpControllerDescriptor controllerDescriptor, Type controllerType)" 
    } 
} 

我現在卡住了，我看不到問題在哪裏。 類別供應商具有這樣的構造：

/// <summary> 
/// Default constructor 
/// </summary> 
public CategoryProvider(IUnitOfWork unitOfWork, ICategoryService service) 
{ 

    // Map our properties 
    _unitOfWork = unitOfWork; 
    _service = service; 
} 

和CategoryService有一個構造函數是這樣的：

/// <summary> 
/// The default constructor 
/// </summary> 
/// <param name="unitOfWork"></param> 
public CategoryService(IUnitOfWork unitOfWork) 
    : base(unitOfWork) 
{ 
} 

，最後是的UnitOfWork具有這樣的構造：

/// <summary> 
/// Default constructor 
/// </summary> 
/// <param name="context">The database context</param> 
public UnitOfWork(DbContext context) 
{ 
    _context = context; 
    _repositories = new Dictionary<Type, object>(); 
} 

從我可以告訴，一切都設置了c orrectly。 任何人都可以發現任何我忘記做的事嗎？

Answer 1

我發現了這個問題，我用HttpConfiguration來設置依賴解析器，它應該是GlobalConfiguration.Configuration。

所以，當我改變了我的專線：

config.DependencyResolver = new AutofacWebApiDependencyResolver(container); 

到

GlobalConfiguration.Configuration.DependencyResolver = new AutofacWebApiDependencyResolver(container); 

一切都開始工作。

Answer 2

嘗試只是建立你的容器前登錄已加載到應用程序域的執行上下文的組件：

var assemblies = AppDomain.CurrentDomain.GetAssemblies(); builder.RegisterAssemblyModules(assemblies);

/// <summary> 
/// Configures Autofac DI/IoC 
/// </summary> 
/// <param name="app"></param> 
/// <param name="config"></param> 
private IContainer ConfigureInversionOfControl(IAppBuilder app, HttpConfiguration config) 
{ 

    // Create our container 
    var builder = new ContainerBuilder(); 

    // You can register controllers all at once using assembly scanning... 
    builder.RegisterApiControllers(Assembly.GetExecutingAssembly()); 

    // Register our module 
    builder.RegisterModule(new AutofacModule()); 

    // [!!!] ** Register assemblies of the current domain ** 
    var assemblies = AppDomain.CurrentDomain.GetAssemblies(); 
    builder.RegisterAssemblyModules(assemblies); 

    // Build 
    var container = builder.Build(); 

    // Lets Web API know it should locate services using the AutofacWebApiDependencyResolver 
    config.DependencyResolver = new AutofacWebApiDependencyResolver(container); 

    // Return our container 
    return container; 
} 

而且不要忘了定義：

public class AutofacModule : Module 
{ 
    protected override void Load(ContainerBuilder builder) 
    { 

     ... 

     builder.RegisterControllers(typeof(WebApiApplication).Assembly); 
     builder.RegisterApiControllers(typeof(WebApiApplication).Assembly); 
    } 
}