所以我正在尝试实现将我的DBContext类作为依赖注入作为ServiceProvider链接的IoC。
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，我试着谷歌搜索但我无法真正找到解决方案。我试过询问我校园里的一些精英程序员，但是他们没有专门使用ASPnet Core，所以他们不知道是不是因为我的演员或者是因为ASPnet Core
应用程序启动异常：System.InvalidCastException：无法转换类型为“Microsoft.Extensions.DependencyInjection.ServiceLookup.ServiceProviderEngineScope”的对象以键入“Microsoft.Extensions.DependencyInjection.ServiceProvider”。在F：\ Developement \ SpackkMVC \ Spackk \ Spackk \ Startup.cs中的Spackk.Startup.Configure（IApplicationBuilder app，IHostingEnvironment env，IServiceProvider serviceProvider）：第44行---从抛出异常的上一个位置开始的堆栈跟踪结束 - - Microsoft.AspNetCore.Hosting.ConventionBasedStartup.Configure（IApplicationBuilder app）at Microsoft.AspNetCore.HostFilteringStartupFilter。<> c__DisplayClass0_0.b__0（IApplicationBuilder app）at Microsoft.AspNetCore.Hosting.Internal.AutoRequestServicesStartupFilter。<> c__DisplayClass0_0.b__0（IApplicationBuilder builder） ）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：无法转换类型为'Microsoft.Extensions.DependencyInjection.ServiceLookup的对象.ServiceProviderEngineScope'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）：第44行---从抛出异常的上一个位置开始的堆栈跟踪结束 - - Microsoft.AspNetCore.Hosting.ConventionBasedStartup.Configure（IApplicationBuilder app）at Microsoft.AspNetCore.HostFilteringStartupFilter。<> c__DisplayClass0_0.b__0（IApplicationBuilder app）at Microsoft.AspNetCore.Hosting.Internal.AutoRequestServicesStartupFilter。<> c__DisplayClass0_0.b__0（IApplicationBuilder builder） ）在Microsoft.AspNetCore.Hosting.Internal.WebHost.BuildApplication（）
这是代码在Startup中的外观
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?}");
});
}
}
}
这是发生错误的类所在的位置;
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; }
}
}
好吧，错误是显而易见的，并且在这一行上显然是失败的：
IocContainer.Provider = (ServiceProvider)serviceProvider;
serviceProvider有一个ServiceProviderEngineScope的例子，它不能被投射到ServiceProvider。仅仅因为它们都实现IServiceProvider并不意味着你可以从一个实现转换到另一个实现。
但是，这一切都是错的。像错了。我希望我能更加重视这一点。想象一下，一个20英尺的广告牌，闪烁的LED呈霓虹红色。要么使用DI，要么不使用，但是用一些依赖注入的对象填充一些静态类是完全错误的，然后期望能够在任何你喜欢的地方使用它。