带有 Web API 2 的 Autofac - 无参数构造函数错误

Question

我正在尝试在我的 Web API 2 项目中设置 Autofac。我以前只用过几次。我使用 Nuget 并安装了 Autofac 和 Autofac.WebApi2。 然后在我的 Startup 课程中，我这样做了：

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;
    }
}

我创建的模块如下所示：

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();
    }
}

我添加了一个提供程序作为我的 API 构造函数的参数，如下所示：

// 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，我收到了这个错误：

{
    "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，我根本看不出问题出在哪里。 类别提供者有一个这样的构造函数：

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

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

CategoryService 有一个这样的构造函数：

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

最后，UnitOfWork 有一个这样的构造函数：

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

据我所知，一切都设置正确。 谁能发现我忘记做的事情？

Answer 1

我发现了问题，我用HttpConfiguration设置依赖解析器，应该是GlobalConfiguration.Configuration。

所以当我改变我的线路时：

config.DependencyResolver = new AutofacWebApiDependencyResolver(container);

到

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

一切都开始工作了。

Answer 2

尝试在构建容器之前注册已加载到应用程序域的执行上下文中的程序集：

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;
}

别忘了定义：

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

      ...

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