c# - 配置方法中的ASP Net Core请求服务返回null

我正试图在configure方法中获得一些服务，以便可以更容易地使用它们来创建数据库。
所以我已经在我的configure方法中注入了iserviceprovider，但是每次我这样做时：var service = serviceProvider.GetService<UserService>();它都返回空值…
这是我的代码：

public class Startup
    {
        public Startup(IHostingEnvironment env)
        {
            var builder = new ConfigurationBuilder()
                .SetBasePath(env.ContentRootPath)
                .AddJsonFile("appsettings.json", optional: true, reloadOnChange: true)
                .AddJsonFile($"appsettings.{env.EnvironmentName}.json", optional: true);

            builder.AddEnvironmentVariables();
            Configuration = builder.Build();
        }

        public IConfigurationRoot Configuration { get; }

        // This method gets called by the runtime. Use this method to add services to the container
        public void ConfigureServices(IServiceCollection services)
        {

            services.AddDbContext<ApplicationDbContext>(options =>
              options.UseSqlServer(this.Configuration.GetConnectionString("DbConnectionString")));

            // Add framework services.
            services.AddIdentity<IdentityUser, IdentityRole>().AddEntityFrameworkStores<IdentityDbContext>().AddDefaultTokenProviders();
            string connection = this.Configuration.GetConnectionString("DbConnectionString");
            services.AddEntityFramework();
            services.AddDbContext<ApplicationDbContext>(options => options.UseSqlServer(connection));
            services.AddIdentity<ApplicationUser, IdentityRole>()
                .AddEntityFrameworkStores<ApplicationDbContext>()
                .AddDefaultTokenProviders();
            services.Configure<AppSettings>(this.Configuration.GetSection("AppSettings"));

            services.AddScoped<IsAuthorized>();
            services.AddSingleton<UserManager<ApplicationUser>>();
            services.AddTransient<IUsersService, UserService>();

            services.AddMvc(config => { config.Filters.Add(typeof(SingletonUsers)); });
        }

        // This method gets called by the runtime. Use this method to configure the HTTP request pipeline
        public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory, IServiceProvider services)
        {
            loggerFactory.AddConsole(this.Configuration.GetSection("Logging"));
            loggerFactory.AddDebug();

            app.UseMvc();

            // This returns the context.
            var context = services.GetService<ApplicationDbContext>();

            // This returns null.
            var userService = services.GetService<UserService>();

            // Can't work without the UserService
            MyDbInitializer.Initialize(context, userService);
        }
    }

最佳答案

当您使用

services.AddTransient<IUsersService, UserService>();

而不是

var userService = services.GetService<UserService>();

您需要询问接口类型：

var userService = services.GetService<IUserService>();

关于c# - 配置方法中的ASP Net Core请求服务返回null，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/43065566/