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

Question

所以我试图实现我的 IoC，将我的 DBContext 类链接为依赖注入作为服务提供者。

我在启动 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，但我无法真正找到解决方案。我尝试询问校园里一些更精英的程序员，但他们没有专门使用 ASPnet Core，所以他们不知道这是因为我的选角还是因为 ASPnet Core

应用程序启动异常：System.InvalidCastException：无法将类型“Microsoft.Extensions.DependencyInjection.ServiceLookup.ServiceProviderEngineScope”的对象强制转换为类型“Microsoft.Extensions.DependencyInjection.ServiceProvider”。在 F:\Developement\SpackkMVC\Spackk\Spackk\Startup.cs 中的 Spackk.Startup.Configure(IApplicationBuilder app, IHostingEnvironment env, IServiceProvider serviceProvider) 处：第 44 行 --- 抛出异常的上一个位置的堆栈跟踪结束 --- - 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 构建器）在 Microsoft.AspNetCore.Hosting.Internal.WebHost.BuildApplication() crit：Microsoft.AspNetCore.Hosting.Internal.WebHost[6] 应用程序启动异常 System.InvalidCastException：无法转换类型为“Microsoft.Extensions.DependencyInjection.ServiceLookup”的对象.ServiceProviderEngineScope”以键入“Microsoft.Extensions.DependencyInjection.ServiceProvider”。在 F:\Developement\SpackkMVC\Spackk\Spackk\Startup.cs 中的 Spackk.Startup.Configure(IApplicationBuilder app, IHostingEnvironment env, IServiceProvider serviceProvider) 处：第 44 行 --- 抛出异常的上一个位置的堆栈跟踪结束 --- - 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 构建器）在 Microsoft.AspNetCore.Hosting.Internal.WebHost.BuildApplication()

这是启动时代码的样子

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; }
    }
}

应用程序数据库上下文

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/IoC容器

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，并且很明显在这一行失败了：

IocContainer.Provider = (ServiceProvider)serviceProvider;

serviceProvider有一个 的实例ServiceProviderEngineScope，无法转换为ServiceProvider。仅仅因为它们都实现IServiceProvider并不意味着您可以从一种实现转换到另一种实现。

然而，这整件事都是错误的。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，上面闪烁着明亮的霓虹红色 LED。要么使用 DI 要么不使用 DI ，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。