C# – Unable to resolve service for type ‘Microsoft.Extensions.Logging.ILogger`1[WebApplication1.Startup]’

asp.net-coreasp.net-core-3.0crazor-pagesvisual-studio-2019

I created an ASP.NET Core 3.0 Web Application with the default template in Visual Studio 2019 Preview 2.2 and tried to inject an ILogger in Startup:

namespace WebApplication1
{
    public class Startup
    {
        private readonly ILogger _logger;

        public Startup(IConfiguration configuration, ILogger<Startup> logger)
        {
            Configuration = configuration;
            _logger = logger;
        }
        // ...
    }
}

In Program.cs I also call the ConfigureLogging() method:

namespace WebApplication1
{
    public class Program
    {
        public static void Main(string[] args)
        {
            CreateHostBuilder(args).Build().Run();
        }

        public static IHostBuilder CreateHostBuilder(string[] args) =>
            Host.CreateDefaultBuilder(args)
                .ConfigureLogging((hostingContext, logging) =>
                {
                    logging.AddConfiguration(hostingContext.Configuration.GetSection("Logging"));
                    logging.ClearProviders();
                    logging.AddConsole();
                })
                .ConfigureWebHostDefaults(webBuilder =>
                {
                    webBuilder.UseStartup<Startup>();
                });
    }
}

It works in ASP.NET Core 2.x but in ASP.NET Core 3 it fails with the following error:

System.InvalidOperationException: Unable to resolve service for type 'Microsoft.Extensions.Logging.ILogger`1[WebApplication1.Startup]' while attempting to activate 'WebApplication1.Startup'.
   at Microsoft.Extensions.DependencyInjection.ActivatorUtilities.ConstructorMatcher.CreateInstance(IServiceProvider provider)
   at Microsoft.Extensions.DependencyInjection.ActivatorUtilities.CreateInstance(IServiceProvider provider, Type instanceType, Object[] parameters)
   at Microsoft.AspNetCore.Hosting.Internal.GenericWebHostBuilder.UseStartup(Type startupType, HostBuilderContext context, IServiceCollection services)
--- End of stack trace from previous location where exception was thrown ---
   at Microsoft.AspNetCore.Hosting.Internal.GenericWebHostBuilder.<>c__DisplayClass13_0.<UseStartup>b__2(IApplicationBuilder app)
   at Microsoft.AspNetCore.Server.IIS.Core.IISServerSetupFilter.<>c__DisplayClass2_0.<Configure>b__0(IApplicationBuilder app)
   at Microsoft.AspNetCore.HostFilteringStartupFilter.<>c__DisplayClass0_0.<Configure>b__0(IApplicationBuilder app)
   at Microsoft.AspNetCore.Hosting.Internal.GenericWebHostService.StartAsync(CancellationToken cancellationToken)

Any idea on what is causing this behavior?


Below the full Program.cs and Startup.cs files from the default "Web Application" template, only logging was added.

Program.cs

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.AspNetCore;
using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.Logging;

namespace WebApplication1
{
    public class Program
    {
        public static void Main(string[] args)
        {
            CreateHostBuilder(args).Build().Run();
        }

        public static IHostBuilder CreateHostBuilder(string[] args) =>
            Host.CreateDefaultBuilder(args)
                .ConfigureLogging((hostingContext, logging) =>
                {
                    logging.AddConfiguration(hostingContext.Configuration.GetSection("Logging"));
                    logging.ClearProviders();
                    logging.AddConsole();
                })
                .ConfigureWebHostDefaults(webBuilder =>
                {
                    webBuilder.UseStartup<Startup>();
                });
    }
}

Startup.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.HttpsPolicy;
using Microsoft.AspNetCore.Mvc;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Logging;

namespace WebApplication1
{
    public class Startup
    {
        private readonly ILogger _logger;
        public Startup(IConfiguration configuration, ILogger<Startup> logger)
        {
            Configuration = configuration;
            _logger = logger;
        }

        public IConfiguration Configuration { get; }

        // This method gets called by the runtime. Use this method to add services to the container.
        public void ConfigureServices(IServiceCollection services)
        {
            services.Configure<CookiePolicyOptions>(options =>
            {
                // This lambda determines whether user consent for non-essential cookies is needed for a given request.
                options.CheckConsentNeeded = context => true;
                options.MinimumSameSitePolicy = SameSiteMode.None;
            });

            //services.AddTransient(typeof(ILogger<>), (typeof(Logger<>)));

            services.AddMvc()
                .AddNewtonsoftJson();
        }

        // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
        public void Configure(IApplicationBuilder app, IHostingEnvironment env)
        {
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }
            else
            {
                app.UseExceptionHandler("/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.UseRouting(routes =>
            {
                routes.MapApplication();
            });

            app.UseCookiePolicy();

            app.UseAuthorization();
        }
    }
}

Best Answer

Unfortunately, it's not possible to inject ILogger into Startup.cs in ASP.NET Core 3.0 anymore.

https://docs.microsoft.com/en-us/azure/azure-monitor/app/ilogger#capture-ilogger-logs-from-startupcs-and-programcs-in-aspnet-core-apps

Note

In ASP.NET Core 3.0 and later, it is no longer possible to inject ILogger in Startup.cs and Program.cs. See https://github.com/aspnet/Announcements/issues/353 for more details.

EDIT: A possible way of doing logging inside the Configure method in Startup.cs would be:

            using (var logScope = app.ApplicationServices.CreateScope())
            {
                var logger = logScope.ServiceProvider.GetService<ILogger<Startup>>();
                logger.LogInformation("Some information");
            }

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