无法转换类型为“Microsoft.Extensions.DependencyInjection.ServiceLookup.ServiceProviderEngineScope”的对象

Question

所以我正在尝试实现我的 IoC，它将我的 DBContext 类链接为作为 ServiceProvider 的依赖注入。

在启动我的 ASP Core 应用程序时遇到此错误 所以我的问题是；我做错了什么，我尝试用谷歌搜索它，但我真的找不到那种解决方案。 我试着问过我校园里一些比较优秀的程序员，但他们没有专门使用 ASPnet Core，所以他们不知道是因为我的演员还是因为 ASPnet Core

应用程序启动异常：System.InvalidCastException：无法将“Microsoft.Extensions.DependencyInjection.ServiceLookup.ServiceProviderEngineScope”类型的对象转换为“Microsoft.Extensions.DependencyInjection.ServiceProvider”类型。 在 F:\Developement\SpackkMVC\Spackk\Spackk\Startup.cs:line 44 中的 Spackk.Startup.Configure(IApplicationBuilder app, IHostingEnvironment env, IServiceProvider serviceProvider) --- 从先前抛出异常的位置结束堆栈跟踪 --- 在 Microsoft.AspNetCore.Hosting.ConventionBasedStartup.Configure（IApplicationBuilder 应用程序） 在 Microsoft.AspNetCore.HostFilteringStartupFilter.c__DisplayClass0_0.b__0（IApplicationBuilder 应用程序） 在 Microsoft.AspNetCore.Hosting.Internal.AutoRequestServicesStartupFilter.c__DisplayClass0_0.b__0（IApplicationBuilder 生成器） 在 Microsoft.AspNetCore.Hosting.Internal.WebHost.BuildApplication() 暴击：Microsoft.AspNetCore.Hosting.Internal.WebHost[6] 应用程序启动异常 System.InvalidCastException：无法将“Microsoft.Extensions.DependencyInjection.ServiceLookup.ServiceProviderEngineScope”类型的对象转换为“Microsoft.Extensions.DependencyInjection.ServiceProvider”类型。 在 F:\Developement\SpackkMVC\Spackk\Spackk\Startup.cs:line 44 中的 Spackk.Startup.Configure(IApplicationBuilder app, IHostingEnvironment env, IServiceProvider serviceProvider) --- 从先前抛出异常的位置结束堆栈跟踪 --- 在 Microsoft.AspNetCore.Hosting.ConventionBasedStartup.Configure（IApplicationBuilder 应用程序） 在 Microsoft.AspNetCore.HostFilteringStartupFilter.c__DisplayClass0_0.b__0（IApplicationBuilder 应用程序） 在 Microsoft.AspNetCore.Hosting.Internal.AutoRequestServicesStartupFilter.c__DisplayClass0_0.b__0（IApplicationBuilder 生成器） 在 Microsoft.AspNetCore.Hosting.Internal.WebHost.BuildApplication()

这就是代码在 Startup 中的样子

using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Mvc;
using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using System;

namespace Spackk
{
    public class Startup
    {
        private readonly string UserGuid = Guid.NewGuid().ToString();
        public Startup(IConfiguration configuration)
        {
            Configuration = configuration;
        }

        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)
        {
            //add ApplicationDbContext to DI
            services.AddDbContext<ApplicationDbContext>(options => options.UseSqlServer("Server=.;Database=SpackkDB;Trusted_Connection;MultipleActiveResultSets=true"));
            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.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_1);
        }

        // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
        public void Configure(IApplicationBuilder app, IHostingEnvironment env, IServiceProvider serviceProvider)
        {

            //Store isntance of the DI Service provider so our application can access iot anywhere
            IocContainer.Provider = (ServiceProvider)serviceProvider;
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }
            else
            {
                app.UseExceptionHandler("/Home/Error");
                app.UseHsts();
            }

            app.UseHttpsRedirection();
            app.UseStaticFiles();
            app.UseCookiePolicy();

            app.UseMvc(routes =>
            {
                routes.MapRoute(
                    name: "default",
                    template: "{controller=Home}/{action=Index}/{id?}");
            });
        }
    }
}

这是发生错误的类；

对于上下文，我还将提供 IoC/IoCContainer/ApplicationDbContext 和模型；

using System.ComponentModel.DataAnnotations;

namespace Spackk.Models
{
    public class UserModel
    {
        [Key]
        public string Id { get; set; }
        [Required]
        [MaxLength(255)]
        [Display(Name = "UserName")]
        public string Username { get; set; }
        [Required]
        [MaxLength(255)]
        [Display(Name = "DisplayName")]
        public string DisplayName { get; set; }
        [Required]
        [MaxLength(255)]
        [DataType(DataType.Password)]
        [Display(Name = "Password")]
        public string Password { get; set; }
        [Required]
        [MaxLength(255)]
        [DataType(DataType.EmailAddress)]
        [Display(Name = "Email")]
        public string Email { get; set; }
    }
}

ApplicationDbContext

using Microsoft.EntityFrameworkCore;
using Spackk.Models;
using System;
using System.Linq;

namespace Spackk
{
    public class ApplicationDbContext : DbContext
    {
        public string Id { get; set; } = Guid.NewGuid().ToString("N");
        public DbSet<UserModel> Users { get; set; }
        /// <summary>
        /// 
        /// </summary>
        /// <param name="options"></param>
        public ApplicationDbContext(DbContextOptions<ApplicationDbContext> options) : base(options)
        {

        }

        protected override void OnModelCreating(ModelBuilder mBuilder)
        {
            base.OnModelCreating(mBuilder);

            mBuilder.Entity<UserModel>().HasIndex(a => a.DisplayName);
        }
    }
}

IoC/IoCContainer

using Microsoft.Extensions.DependencyInjection;

namespace Spackk
{
    public class IoC
    {

        /// <summary>
        /// The scoped instance of the <see cref="ApplicationDbContext()"/>
        /// </summary>
        public static ApplicationDbContext ApplicationDbContext => IocContainer.Provider.GetService<ApplicationDbContext>();
    }
    /// <summary>
    /// the dependenc injection container making use of the built in .Net Core service provider
    /// </summary>
    public class IocContainer
    {
        /// <summary>
        /// the service provider for the is application
        /// </summary>
        public static ServiceProvider Provider { get; set; }
    }
}

Answer 1

嗯，错误是明确的，而且很明显在这一行上失败了：

IocContainer.Provider = (ServiceProvider)serviceProvider;

serviceProvider 有一个ServiceProviderEngineScope 的实例，它不能转换为ServiceProvider。仅仅因为它们都实现了IServiceProvider 并不意味着您可以从一个实现转换到另一个实现。

然而，整个事情只是错。喜欢错误。我希望我能更加强调这一点。想象一个 20 英尺高的广告牌，上面有明亮的霓虹红色闪烁的 LED。要么使用 DI，要么不要，但是仅仅用一些依赖注入的对象填充一些静态类然后期望能够在任何你喜欢的地方使用它是完全错误的。