在 ASP.NET Core 3.1 的 Startup.cs 中注入服务

Question

I am working on a .NET Core 3.1 application. I have a requirement where i have to inject a service in Startup.cs. My code is:

Program.cs:

public class Program
    {
        public static void Main(string[] args)
        {
            CreateHostBuilder(args).Build().Run();
        }

        public static IHostBuilder CreateHostBuilder(string[] args) =>
            Host.CreateDefaultBuilder(args)
                .ConfigureServices(servicesCollection =>
                {
                    servicesCollection.AddScoped<IUnauthorizedAccessService, UnauthorizedAccessService>();
                })
                .ConfigureWebHostDefaults(webBuilder =>
                {
                    webBuilder.UseStartup<Startup>();
                });
    }

Startup.cs:

public Startup(IConfiguration configuration, IUnauthorizedAccessService unauthorizedAccessService)
{
        Configuration = configuration;
        _unauthorizedAccessService = unauthorizedAccessService;
}

public IConfiguration Configuration { get; }
public IUnauthorizedAccessService _unauthorizedAccessService { get; set; }

When i run the code, i get the following exception:

Unable to resolve service for type 'Interface.Service.IUnauthorizedAccessService' while attempting to activate 'Website.Startup'.'

How can i inject the service in Startup.cs? I have even tried it getting in Configure method. But then, i get the exception at repository level. Code:

public void Configure(IApplicationBuilder app, IWebHostEnvironment env, IUnauthorizedAccessService unauthorizedAccessService)
        {
            _unauthorizedAccessService = unauthorizedAccessService;

            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }
            else
            {
                app.UseExceptionHandler("/Home/Error");
                // The default HSTS value is 30 days. You may want to change this for production scenarios, see https://aka.ms/aspnetcore-hsts.
                app.UseHsts();
            }
            app.UseHttpsRedirection();
            app.UseStaticFiles();
            app.UseSession();
            app.UseRouting();

            app.UseAuthentication();
            app.UseAuthorization();
            app.UseCookiePolicy(new CookiePolicyOptions
            {
                MinimumSameSitePolicy = SameSiteMode.Strict,
            });

            app.UseEndpoints(endpoints =>
            {
                endpoints.MapControllerRoute(
                    name: "default",
                    pattern: "{controller=User}/{action=Index}/{id?}");
            });
        }

I have a method RegisterDatabase which is being called from ConfigureServices . Code:

private void RegisterDatabase(IServiceCollection services)
        {
            services.AddDbContext<TrainingContext>(options =>
                    options.UseSqlServer(Configuration.GetConnectionString("DefaultConnection")));
        }

Service code is:

public class UnauthorizedAccessService : IUnauthorizedAccessService
    {
        private readonly IEventLogRepository _eventLogRepository;
        public UnauthorizedAccessService(IEventLogRepository eventLogRepository)
        {
            _eventLogRepository = eventLogRepository;
        }

        public async Task<BaseResponse> LogUnauthorizedAccessInDB(string user, string url, string sessionId)
        {
            try
            {
                EventLog eventLog = new EventLog();
                eventLog.Httpsession = sessionId;
                eventLog.AppUserName = user;
                eventLog.EventDateTime = DateTime.Now;
                eventLog.MessageLevel = 3;
                eventLog.Message = url;

                await _eventLogRepository.Add(eventLog);
            }
            catch(Exception ex)
            {

            }

            return HelperService.Response(null, null);
        }
    }

When Adding the object, i get the exception

Cannot access a disposed context instance. A common cause of this error is disposing a context instance that was resolved from dependency injection and then later trying to use the same context instance elsewhere in your application. This may occur if you are calling 'Dispose' on the context instance, or wrapping it in a using statement. If you are using dependency injection, you should let the dependency injection container take care of disposing context instances.
Object name: 'TrainingContext'.

All of my other repositories are working but, getting exception only at this point. What can be the possible issue? Any help would be much appreciated.

Basically, what i am trying to achieve is that i want to log unauthorized access to my site in Database. Code is:

services.AddAuthentication(CookieAuthenticationDefaults.AuthenticationScheme)
                .AddCookie(o =>
                {
                    o.AccessDeniedPath = "/Home/Error";
                    o.LoginPath = "/Login";
                    o.SlidingExpiration = false;
                    o.Events = new CookieAuthenticationEvents
                    {
                        //OnRedirectToAccessDenied = new Func<RedirectContext<CookieAuthenticationOptions>, Task>(context =>

                        OnRedirectToAccessDenied = new Func<RedirectContext<CookieAuthenticationOptions>, Task>(test)
                    };
                });

test method is:

private async Task<Task> test (RedirectContext<CookieAuthenticationOptions> context)
        {
            string user = context.HttpContext.User.Identity.Name;
            string url = "/" + context.Request.Host.Value + "/" + context.Request.RouteValues["controller"] + "/" + context.Request.RouteValues["action"];
            string sessionId = context.HttpContext.Session.Id;

            await _unauthorizedAccessService.LogUnauthorizedAccessInDB(user, url, sessionId);

            context.Response.Redirect("/Home/Error");
            return context.Response.CompleteAsync();
        }

Answer 1

Startup.cs is designed for configuring own services and pipeline configuration. You can not inject your custom services in constructor just because they are not configured yet.

Docs:

The host provides services that are available to the Startup class constructor. The app adds additional services via ConfigureServices. Both the host and app services are available in Configure and throughout the app.

Answer 2

You need to create a scoped object that implements CookieAuthenticationEvents . For example:

using Microsoft.AspNetCore.Authentication;
using Microsoft.AspNetCore.Authentication.Cookies;
using System.Threading.Tasks;

namespace MyApplication.Services
{
    public class MyCookieAuthenticationEvents : CookieAuthenticationEvents
    {
        private readonly IUnauthorizedAccessService _unauthorizedAccessService;

        public MyCookieAuthenticationEvents(
            IUnauthorizedAccessService unauthorizedAccessService)
        {
            _unauthorizedAccessService = unauthorizedAccessService;
        }

        public override Task RedirectToAccessDenied(
            RedirectContext<CookieAuthenticationOptions> context)
        {
            // TODO: you can use _unauthorizedAccessService here
            return base.RedirectToAccessDenied(context);
        }
    }
}

To inject this, you'd do it as so:

services.AddAuthentication(CookieAuthenticationDefaults.AuthenticationScheme)
    .AddCookie(options =>
    {
        options.EventsType = typeof(MyCookieAuthenticationEvents);
    });

services.AddScoped<MyCookieAuthenticationEvents>();
services.AddScoped<IUnauthorizedAccessService, UnauthorizedAccessService>();

Make sure you remove that IUnauthorizedAccessService from your program.cs . You don't inject there. You inject in your Configure method.

This is how you do proper dependency injection. You don't do what the accepted answer is doing. That is probably one of the most unorthodox things I have ever seen in a long time.