.net Core 6 - 尝试激活时无法解析服务类型
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【中文标题】.net Core 6 - 尝试激活时无法解析服务类型【英文标题】：.net Core 6 - Unable to resolve service for type while attempting to activate 【发布时间】：2021-12-25 18:04:11 【问题描述】：在我的 ASP.NET Core 应用程序中，我收到以下错误：
InvalidOperationException：无法解析服务类型 尝试激活时出现“mvc_net6.Service.DB_Context” 'mvc_net6.Controllers.StudentController'。
StudentController StudentController 是通过 Scaffolds 创建到视图的，如下所示：
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.Rendering;
using Microsoft.EntityFrameworkCore;
using mvc_net6.Models;
using mvc_net6.Service;
namespace mvc_net6.Controllers
public class StudentController : Controller
private readonly DB_Context _context;
public StudentController(DB_Context context)
_context = context;
// GET: Student
public async Task<IActionResult> Index()
return View(await _context.Students.ToListAsync());
// GET: Student/Details/5
public async Task<IActionResult> Details(int? id)
if (id == null)
return NotFound();
var student = await _context.Students
.FirstOrDefaultAsync(m => m.Id == id);
if (student == null)
return NotFound();
return View(student);
// GET: Student/Create
public IActionResult Create()
return View();
// POST: Student/Create
// To protect from overposting attacks, enable the specific properties you want to bind to.
// For more details, see http://go.microsoft.com/fwlink/?LinkId=317598.
[HttpPost]
[ValidateAntiForgeryToken]
public async Task<IActionResult> Create([Bind("Id,Name,CPF,Email")] Student student)
if (ModelState.IsValid)
_context.Add(student);
await _context.SaveChangesAsync();
return RedirectToAction(nameof(Index));
return View(student);
// GET: Student/Edit/5
public async Task<IActionResult> Edit(int? id)
if (id == null)
return NotFound();
var student = await _context.Students.FindAsync(id);
if (student == null)
return NotFound();
return View(student);
// POST: Student/Edit/5
// To protect from overposting attacks, enable the specific properties you want to bind to.
// For more details, see http://go.microsoft.com/fwlink/?LinkId=317598.
[HttpPost]
[ValidateAntiForgeryToken]
public async Task<IActionResult> Edit(int id, [Bind("Id,Name,CPF,Email")] Student student)
if (id != student.Id)
return NotFound();
if (ModelState.IsValid)
try
_context.Update(student);
await _context.SaveChangesAsync();
catch (DbUpdateConcurrencyException)
if (!StudentExists(student.Id))
return NotFound();
else
throw;
return RedirectToAction(nameof(Index));
return View(student);
// GET: Student/Delete/5
public async Task<IActionResult> Delete(int? id)
if (id == null)
return NotFound();
var student = await _context.Students
.FirstOrDefaultAsync(m => m.Id == id);
if (student == null)
return NotFound();
return View(student);
// POST: Student/Delete/5
[HttpPost, ActionName("Delete")]
[ValidateAntiForgeryToken]
public async Task<IActionResult> DeleteConfirmed(int id)
var student = await _context.Students.FindAsync(id);
_context.Students.Remove(student);
await _context.SaveChangesAsync();
return RedirectToAction(nameof(Index));
private bool StudentExists(int id)
return _context.Students.Any(e => e.Id == id);
我有一个文件 DB_Context.cs，其中包含一个类及其实现，如下所示：
using Microsoft.EntityFrameworkCore;
using mvc_net6.Models;
namespace mvc_net6.Service
public class DB_Context : DbContext
public DB_Context(DbContextOptions<DB_Context> options) : base(options)
public DbSet<mvc_net6.Models.Student> Students get; set;
我有一个文件 DB_Factory.cs，其中包含一个类及其实现，如下所示：
namespace mvc_net6
public class BloggingContextFactory : IDesignTimeDbContextFactory<DB_Context>
public DB_Context CreateDbContext(string[] args)
// Replace with your server version and type.
// Use 'MariaDbServerVersion' for MariaDB.
// Alternatively, use 'ServerVersion.AutoDetect(connectionString)'.
var serverVersion = new MariaDbServerVersion(new Version(10, 5, 12));
var optionsBuilder = new DbContextOptionsBuilder<DB_Context>();
optionsBuilder.Usemysql("ConnectionString", serverVersion);
return new DB_Context(optionsBuilder.Options);
My Program.cs 包含从模板默认生成的代码。
var builder = WebApplication.CreateBuilder(args);
// Add services to the container.
builder.Services.AddControllersWithViews();
var app = builder.Build();
IConfiguration configuration = app.Configuration;
// Configure the HTTP request pipeline.
if (!app.Environment.IsDevelopment())
app.UseExceptionHandler("/Home/Error");
// The default HSTS value is 30 days. You may want to change this for production scenarios, see https://aka.ms/aspnetcore-hsts.
app.UseHsts();
app.UseHttpsRedirection();
app.UseStaticFiles();
app.UseRouting();
app.UseAuthorization();
app.MapControllerRoute(
name: "default",
pattern: "controller=Home/action=Index/id?");
app.Run();
//builder.Services.AddDbContext<DB_Context>(options =>
// options.UseMySql(connection, serverVersion));
builder.Services.AddDbContext<DB_Context>(opt =>
opt.UseMySql(connection, serverVersion);
);
app.UseHttpsRedirection();
app.UseStaticFiles();
app.UseRouting();
app.UseAuthorization();
app.MapControllerRoute(
name: "default",
pattern: "controller=Home/action=Index/id?");
app.Run();
但是，在运行系统时，我现在收到以下错误：
watch : Started
Unhandled exception. System.InvalidOperationException: Cannot modify ServiceCollection after application is built.
at Microsoft.AspNetCore.WebApplicationServiceCollection.CheckServicesAccess()
at Microsoft.AspNetCore.WebApplicationServiceCollection.Add(ServiceDescriptor item)
at Microsoft.Extensions.DependencyInjection.Extensions.ServiceCollectionDescriptorExtensions.TryAdd(IServiceCollection collection, ServiceDescriptor descriptor)
at Microsoft.Extensions.DependencyInjection.EntityFrameworkServiceCollectionExtensions.AddCoreServices[TContextImplementation](IServiceCollection serviceCollection, Action`2 optionsAction, ServiceLifetime optionsLifetime)
at Microsoft.Extensions.DependencyInjection.EntityFrameworkServiceCollectionExtensions.AddDbContext[TContextService,TContextImplementation](IServiceCollection serviceCollection, Action`2 optionsAction, ServiceLifetime contextLifetime, ServiceLifetime optionsLifetime)
at Microsoft.Extensions.DependencyInjection.EntityFrameworkServiceCollectionExtensions.AddDbContext[TContextService,TContextImplementation](IServiceCollection serviceCollection, Action`1 optionsAction, ServiceLifetime contextLifetime, ServiceLifetime optionsLifetime)
at Microsoft.Extensions.DependencyInjection.EntityFrameworkServiceCollectionExtensions.AddDbContext[TContext](IServiceCollection serviceCollection, Action`1 optionsAction, ServiceLifetime contextLifetime, ServiceLifetime optionsLifetime)
at Program.<Main>$(String[] args) in /home/r31sr4r/Projects/dotnet_core/mvc_net6/Program.cs:line 31
watch : Exited with error code 134
watch : Waiting for a file to change before restarting dotnet...
【问题讨论】：
【参考方案1】：在您的 program.cs 中，确保注入 db DB_Context
builder.services.AddDbContext<DB_Context>(opt =>
opt.UseMySql("YOUR_CONNECTION_STRING");
);
否则，您不能在controller上使用它
【讨论】：
这对我有用。非常感谢！！！ 很高兴听到这个消息。您可以将答案标记为正确或投赞成票，以便遇到类似问题的其他人会有所帮助【参考方案2】：将您的 dbcontext 配置放在此之前：
var app = builder.Build();
【讨论】：
【参考方案3】：您需要在“var app = builder.Build();”之前进行此注入。
【讨论】：
【参考方案4】：你会得到错误，Cannot modify ServiceCollection after application is built. 以一种非常偷偷摸摸的方式。
我在ConfigureServices 中有一些代码，如下所示：
services.AddAuthentication(options =>
// Set up options...
)
.AddOpenIdConnect(options =>
// Set up options...
services.AddHttpClient<IMyTokenClient, MyTokenClient>(httpClient =>
httpClient.BaseAddress = new Uri(authSettings.Authority);
);
);
您可以看到服务在嵌套闭包中设置不正确。 我将代码更改为：
services.AddAuthentication(options =>
// Set up options...
)
.AddOpenIdConnect(options =>
// Set up options...
);
services.AddHttpClient<IMyTokenClient, MyTokenClient>(httpClient =>
httpClient.BaseAddress = new Uri(authSettings.Authority);
);
这解决了错误。
【讨论】：
谢谢@Jess！！以上是关于.net Core 6 - 尝试激活时无法解析服务类型的主要内容，如果未能解决你的问题，请参考以下文章
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