使用RegisterAssemblyTypes時如何在Autofac中注冊裝飾器？

Question

這是我的代碼

public interface ICommandHandler<T>
{
    void Handle(T command);
}

public class CreateUserCommandHandler : ICommandHandler<CreateUserCommand>
{
    public void Handle(CreateUserCommand command)
    {
        // do something with the command
    }
}

public class LoggingCommandDecorator<TCommand> : ICommandHandler<TCommand>
{
    private readonly ICommandHandler<TCommand> _commandHandler;

    public LoggingCommandDecorator(ICommandHandler<TCommand> commandHandler)
    {
        _commandHandler = commandHandler;
    }

    public void Handle(TCommand command)
    {
        Debug.WriteLine("Logging...");

        _commandHandler.Handle(command);
    }
}

這是我的注冊：

private void SetupAutofac()
{
    var builder = new ContainerBuilder();

    // Register your MVC controllers.
    builder.RegisterControllers(typeof(WebApiApplication).Assembly);

    // OPTIONAL: Register model binders that require DI.
    builder.RegisterModelBinders(Assembly.GetExecutingAssembly());
    builder.RegisterModelBinderProvider();

    var assemblies = AppDomain.CurrentDomain.GetAssemblies();
    builder.RegisterAssemblyTypes(assemblies)
            .As(o => o.GetInterfaces()
            .Where(i => i.IsClosedTypeOf(typeof(ICommandHandler<>)))
            .Select(i => new KeyedService("Handler", i)));

    builder.RegisterGenericDecorator(typeof(LoggingCommandDecorator<>),
                            typeof(ICommandHandler<>),
                            "Handler", "DecoratedHandler");


    var container = builder.Build();

    DependencyResolver.SetResolver(new AutofacDependencyResolver(container));
}

運行此代碼時，出現以下異常：

無法使用可用的服務和參數調用類型為'AspectDemo.Controllers.HomeController'的'Autofac.Core.Activators.Reflection.DefaultConstructorFinder'構造函數：無法解析參數'AspectDemo.Business.ICommandHandler 1[AspectDemo.Business.Users.CreateUserCommand] createUserHandler' of constructor 'Void .ctor(AspectDemo.Business.ICommandHandler 1 [AspectDemo.Business.Users.CreateUserCommand]）。

當我使用以下代碼作為注冊時，我沒有例外，但是我也沒有任何裝飾器。

builder.RegisterAssemblyTypes(assemblies)
       .AsClosedTypesOf(typeof(ICommandHandler<>))
       .AsImplementedInterfaces();

我需要做什么才能使用裝飾器？

注意：現在我只使用一個裝飾器，但是最后我認為我有大約4-5個裝飾器。

Answer 1

當您使用RegisterGenericDecorator方法的toKey參數時，它將導致命名注冊，因此您必須解析一個命名ICommandHandler

builder.RegisterGenericDecorator(
    typeof(LoggingCommandDecorator<>), 
    typeof(ICommandHandler<>), 
    fromKey : "Handler",
    toKey : "DecoratedHandler");

然后您可以像這樣解決它：

container.ResolveKeyed<ICommandHandler<CreateUserCommand>>("DecoratedHandler");

toKey參數是可選的：

builder.RegisterGenericDecorator(
    typeof(LoggingCommandDecorator<>), 
    typeof(ICommandHandler<>), 
    fromKey : "Handler");

然后您可以像這樣解決它：

container.Resolve<ICommandHandler<CreateUserCommand>>();

當您有中間裝飾器時， toKey很有用：

builder.RegisterGenericDecorator(
    typeof(LoggingCommandDecorator<>), 
    typeof(ICommandHandler<>), 
    fromKey : "Original", 
    toKey : "Logging");

builder.RegisterGenericDecorator(
    typeof(AuthorizationCommandDecorator<>), 
    typeof(ICommandHandler<>), 
    fromKey : "Logging");

在這種情況下， ICommandHandler<CreateUserCommand>將由LoggingCommandDecorator<>和AuthorizationCommandDecorator<>裝飾