Asp.netCore 的Startup 不继承接口

    //
        // 摘要:
        //     /// Specify the startup type to be used by the web host. ///
        //
        // 参数:
        //   hostBuilder:
        //     The Microsoft.AspNetCore.Hosting.IWebHostBuilder to configure.
        //
        //   startupType:
        //     The System.Type to be used.
        //
        // 返回结果:
        //     The Microsoft.AspNetCore.Hosting.IWebHostBuilder.
        public static IWebHostBuilder UseStartup(this IWebHostBuilder hostBuilder, Type startupType)
        {
            string name = startupType.GetTypeInfo().Assembly.GetName().Name;
            return hostBuilder.UseSetting(WebHostDefaults.ApplicationKey, name).ConfigureServices(delegate (IServiceCollection services)
            {
                if (IntrospectionExtensions.GetTypeInfo(typeof(IStartup)).IsAssignableFrom(startupType.GetTypeInfo()))
                {
                    services.AddSingleton(typeof(IStartup), startupType);
                }
                else
                {
                    services.AddSingleton(typeof(IStartup), delegate (IServiceProvider sp)
                    {
                        IHostingEnvironment requiredService = sp.GetRequiredService<IHostingEnvironment>();
                        return new ConventionBasedStartup(StartupLoader.LoadMethods(sp, startupType, requiredService.EnvironmentName));
                    });
                }
            });
        }