Autofac与Web API 2 - 无参数构造函数错误

Question

我想在我的Web API 2项目上安装Autofac。我以前只用过它几次。我使用的Nuget安装了两个Autofac和Autofac.WebApi2。 然后在我启动类我这样做：

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; 
    } 
} 

我创建看起来像这样的模块：

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(); 
    } 
} 

而且我加了一个供应商作为一个参数为我这样的API构造：

// Readonly properties 
private readonly ICategoryProvider _provider; 

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

但是，当我尝试调用API（使用邮递员）时，出现此错误：

{ 
    "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)" 
    } 
} 

我现在卡住了，我看不到问题在哪里。 类别供应商具有这样的构造：

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

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

和CategoryService有一个构造函数是这样的：

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

，最后是的UnitOfWork具有这样的构造：

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

从我可以告诉，一切都设置了c orrectly。 任何人都可以发现任何我忘记做的事吗？

Answer 1

我发现了这个问题，我用HttpConfiguration来设置依赖解析器，它应该是GlobalConfiguration.Configuration。

所以，当我改变了我的专线：

config.DependencyResolver = new AutofacWebApiDependencyResolver(container); 

到

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

一切都开始工作。

Answer 2

尝试只是建立你的容器前登录已加载到应用程序域的执行上下文的组件：

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; 
} 

而且不要忘了定义：

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

     ... 

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