无法解析类型为“ Microsoft.Extensions.Logging.ILogger`1 [WebApplication1.Startup]”的服务

Question

我在Visual Studio 2019 Preview 2.2中使用默认模板创建了ASP.NET Core 3.0 Web应用程序，并尝试在启动中注入ILogger：

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

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

在Program.cs中，我还调用ConfigureLogging（）方法：

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>();
                });
    }
}

它在ASP.NET Core 2.x中工作，但在ASP.NET Core 3中失败，并显示以下错误：

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)

对导致此行为的原因有任何想法吗？

---

在默认“ Web应用程序”模板的完整Program.cs和Startup.cs文件下面，仅添加了日志记录。

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>();
                });
    }
}

启动文件

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();
        }
    }
}

Answer 1

不幸的是，再也无法ILogger在ASP.NET Core 3.0中注入Startup.cs了。

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

注意

在ASP.NET Core 3.0和更高版本中，不再可能在Startup.cs和Program.cs中注入ILogger。有关更多详细信息，请参见 https://github.com/aspnet/Announcements/issues/353。

Answer 2

ILogger这可以通过手动注册以使用 Startup 类作为类型来解决。

例子：

public void ConfigureServices(IServiceCollection services)
{
    // Normal AddLogging
    services.AddLogging();

    // Additional code to register the ILogger as a ILogger<T> where T is the Startup class
    services.AddSingleton(typeof(ILogger), typeof(Logger<Startup>)); 
  
    // ...
}

Answer 3

如果你想在调用 Configure() 之后记录事情，你仍然可以通过方法注入来注入 ILogger（与首选的构造函数注入相反：

public void Configure(IApplicationBuilder app, IWebHostEnvironment env, ILogger<TStartup> logger)
{
     _logger = logger;
     ...
}

Answer 4

您是否已经使用 ServiceCollection 来注册 Logger 了！它应该在这里。

serviceProvider.AddTransient(typeof(ILogger<>), (typeof(Logger<>));

或者你说，这是 Program.cs 的示例

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

    public static IWebHost BuildWebHost(string[] args) =>  
        WebHost.CreateDefaultBuilder(args)  
            .ConfigureLogging(logging => logging.SetMinimumLevel(LogLevel.Warning))  
            .UseStartup<Startup>()  
            .Build();  
}