Middleware in Bot framework composer 2.x

[ic202]

Is there an example for programming Middleware with Version 2.x?
I was picking something fruit but it doesn't work:

         services.AddSingleton(sp => new QnAMiddleware(sp.GetService<UserState>()));
        services.AddSingleton<IBotFrameworkHttpAdapter, AdapterWithErrorHandler>();

public class AdapterWithErrorHandler : CloudAdapter
{
public AdapterWithErrorHandler(IConfiguration configuration, IHttpClientFactory httpClientFactory, ILogger logger, QnAMiddleware qnAMiddleware, ConversationState conversationState = default)
: base(configuration, httpClientFactory, logger)
{
if (qnAMiddleware == null)
{
throw new NullReferenceException(nameof(qnAMiddleware));
}

        Use(qnAMiddleware);

    }
}

public class QnAMiddleware : IMiddleware
{
public QnAMiddleware(UserState userState)
{

    }
    public async Task OnTurnAsync(ITurnContext turnContext, NextDelegate next, CancellationToken cancellationToken = default)
    {
        await next(cancellationToken);
    }
}

thank you

[AntonioChiancone]

Hi, in Startup.cs > public void ConfigureServices(IServiceCollection services)

        services.AddSingleton<IMiddleware>(_ => new QnAMiddleware());