如何在 ASP.NET Core 1.0 中的 DI 中的 Startup class 中添加 IHttpContextAccessor？

Question

在 ASP.NET Core RC 1 中，我使用以下代码检索上下文的值（页面的完整地址）。然后我在配置中记录了这个值。

public class Startup
{
        public IConfigurationRoot Configuration { get; set; }
        private IHostingEnvironment CurrentEnvironment { get; set; }
        private IHttpContextAccessor HttpContextAccessor { get; set; }
        public Startup(IHostingEnvironment env,
                IHttpContextAccessor httpContextAccessor)
            {                
                var builder = new ConfigurationBuilder()
                    .SetBasePath(env.ContentRootPath)
                    .AddJsonFile("appsettings.json", optional: true, reloadOnChange: true)
                    .AddJsonFile($"appsettings.{env.EnvironmentName}.json", optional: true);
    
                if (env.IsDevelopment())
                {
                    builder.AddUserSecrets();
                }
                builder.AddEnvironmentVariables();
                Configuration = builder.Build();
                CurrentEnvironment = env;
                HttpContextAccessor = httpContextAccessor;
            }
        public void ConfigureServices(IServiceCollection services)
        {
        ...
        
        services.AddOptions();
        services.Configure<WebAppSettings>(configuration);
        services.Configure<WebAppSettings>(settings =>
        {
            ...
            settings.WebRootPath = CurrentEnvironment.WebRootPath;
            settings.DomainUrl = HttpContextAccessor.HttpContext.Request.Host.ToUriComponent();
        });
        }
   }

现在我开始在 ASP.NET Core 1.0 上更新项目。但是在网站启动期间我收到以下错误：

System.InvalidOperationException Unable to resolve service for type 'Microsoft.AspNetCore.Http.IHttpContextAccessor' while attempting to activate 'MyProject.Startup'.

at Microsoft.Extensions.Internal.ConstructorMatcher.CreateInstance(IServiceProvider provider) at Microsoft.Extensions.Internal.ActivatorUtilities.CreateInstance(IServiceProvider provider, Type instanceType, Object[] parameters) at Microsoft.Extensions.Internal.ActivatorUtilities.GetServiceOrCreateInstance(IServiceProvider provider, Type type) at Microsoft.Extensions.DependencyInjection.ActivatorUtilities.GetServiceOrCreateInstance(IServiceProvider provider, Type type) at Microsoft.AspNetCore.Hosting.Internal.StartupLoader.LoadMethods(IServiceProvider services, Type startupType, string environmentName) at Microsoft.AspNetCore.Hosting.<>c__DisplayClass1_0.b__1(IServiceProvider sp) at Microsoft.Extensions.DependencyInjection.ServiceLookup.FactoryService.Invoke(ServiceProvider provider) at Microsoft.Extensions.DependencyInjection.ScopedCallSite.Invoke(ServiceProvider provider) at Microsoft.Extensions.DependencyInjection.SingletonCallSite.Invoke(ServiceProvider provider) at Microsoft.Extensions.DependencyInjection.<>c__DisplayClass12_0.b__0(ServiceProvider provider) at Microsoft.Extensions.DependencyInjection.ServiceProvider.GetService(Type serviceType) at Microsoft.Extensions.DependencyInjection.ServiceProviderServiceExtensions.GetRequiredService(IServiceProvider provider, Type serviceType) at Microsoft.Extensions.DependencyInjection.ServiceProviderServiceExtensions.GetRequiredService(IServiceProvider provider) at Microsoft.AspNetCore.Hosting.Internal.WebHost.EnsureStartup() at Microsoft.AspNetCore.Hosting.Internal.WebHost.EnsureApplicationServices() at Microsoft.AspNetCore.Hosting.Internal.WebHost.BuildApplication()

.NET Framework X64 v4.0.30319.42000 | Microsoft.AspNetCore.Hosting version 1.0.0-rtm-21431 | Microsoft Windows 6.1.7601 S

如何在应用程序启动期间获取新版本的 IHttpContextAccessor？

Answer 1

它不再是默认服务。您必须在 Startup.cs

中配置它

services.TryAddSingleton<IHttpContextAccessor, HttpContextAccessor>();
services.TryAddSingleton<IActionContextAccessor, ActionContextAccessor>();

更新：在ASP.NET Core 2.1 中，添加了the AddHttpContextAccessor helper extension method 以正确注册具有正确生命周期（单例）的IHttpContextAccessor。因此，在 ASP.NET Core 2.1 及更高版本中，代码应为

services.AddHttpContextAccessor();
services.TryAddSingleton<IActionContextAccessor, ActionContextAccessor>();

来源：https://github.com/aspnet/Hosting/issues/793

Answer 2

可以这样添加。

services.AddSingleton<IHttpContextAccessor, HttpContextAccessor>();

Answer 3

.Net 6可以这样添加

builder.Services.AddSingleton();