ASP.NET Core Dependency Injection错误:尝试激活时无法解析类型服务

Question

我创建了一个.NET Core MVC应用程序,并使用依赖注入和存储库模式将一个存储库注入我的控制器.但是,我收到一个错误:

InvalidOperationException:尝试激活"WebApplication1.Controllers.BlogController"时,无法解析类型"WebApplication1.Data.BloggerRepository"的服务.

型号(Blog.cs)

namespace WebApplication1.Models
{
    public class Blog
    {
        public int BlogId { get; set; }
        public string Url { get; set; }
    }
}

DbContext(BloggingContext.cs)

using Microsoft.EntityFrameworkCore;
using WebApplication1.Models;

namespace WebApplication1.Data
{
    public class BloggingContext : DbContext
    {
        public BloggingContext(DbContextOptions<BloggingContext> options)
            : base(options)
        { }
        public DbSet<Blog> Blogs { get; set; }
    }
}

存储库(IBloggerRepository.cs和BloggerRepository.cs)

using System;
using System.Collections.Generic;
using WebApplication1.Models;

namespace WebApplication1.Data
{
    internal interface IBloggerRepository : IDisposable
    {
        IEnumerable<Blog> GetBlogs();

        void InsertBlog(Blog blog);

        void Save();
    }
}

using System;
using System.Collections.Generic;
using System.Linq;
using WebApplication1.Models;

namespace WebApplication1.Data
{
    public class BloggerRepository : IBloggerRepository
    {
        private readonly BloggingContext _context;

        public BloggerRepository(BloggingContext context)
        {
            _context = context;
        }

        public IEnumerable<Blog> GetBlogs()
        {
            return _context.Blogs.ToList();
        }

        public void InsertBlog(Blog blog)
        {
            _context.Blogs.Add(blog);
        }

        public void Save()
        {
            _context.SaveChanges();
        }

        private bool _disposed;

        protected virtual void Dispose(bool disposing)
        {
            if (!_disposed)
            {
                if (disposing)
                {
                    _context.Dispose();
                }
            }
            _disposed = true;
        }

        public void Dispose()
        {
            Dispose(true);
            GC.SuppressFinalize(this);
        }
    }
}

Startup.cs(相关代码)

public void ConfigureServices(IServiceCollection services)
{
    // Add framework services.
    services.AddDbContext<BloggingContext>(options =>
        options.UseSqlServer(Configuration.GetConnectionString("DefaultConnection")));

    services.AddScoped<IBloggerRepository, BloggerRepository>();

    services.AddMvc();

    // Add application services.
    services.AddTransient<IEmailSender, AuthMessageSender>();
    services.AddTransient<ISmsSender, AuthMessageSender>();
}

控制器(BlogController.cs)

using System.Linq;
using Microsoft.AspNetCore.Mvc;
using WebApplication1.Data;
using WebApplication1.Models;

namespace WebApplication1.Controllers
{
    public class BlogController : Controller
    {
        private readonly IBloggerRepository _repository;

        public BlogController(BloggerRepository repository)
        {
            _repository = repository;
        }

        public IActionResult Index()
        {
            return View(_repository.GetBlogs().ToList());
        }

        public IActionResult Create()
        {
            return View();
        }

        [HttpPost]
        [ValidateAntiForgeryToken]
        public IActionResult Create(Blog blog)
        {
            if (ModelState.IsValid)
            {
                _repository.InsertBlog(blog);
                _repository.Save();
                return RedirectToAction("Index");
            }
            return View(blog);
        }
    }
}

我不确定我做错了什么.有任何想法吗？

Answer 1

例外情况说它无法解析服务,WebApplication1.Data.BloggerRepository因为控制器上的构造函数要求使用具体类而不是接口.所以改变一下:

public BlogController(IBloggerRepository repository)
//                    ^
//                    Add this!
{
    _repository = repository;
}

Answer 2

我遇到了这个问题，因为在依赖项注入设置中，我缺少存储库的依赖项，而该存储库是控制器的依赖项：

services.AddScoped<IDependencyOne, DependencyOne>();    <-- I was missing this line!
services.AddScoped<IDependencyTwoThatIsDependentOnDependencyOne, DependencyTwoThatIsDependentOnDependencyOne>();

Answer 3

在我的情况下,我试图为一个需要构造函数参数的对象进行依赖注入.在这种情况下,在启动期间,我只是从配置文件中提供了参数,例如:

var config = Configuration.GetSection("subservice").Get<SubServiceConfig>();
services.AddScoped<ISubService>(provider => new SubService(config.value1, config.value2));

Answer 4

Public void ConfigureServices(IServiceCollection services)
{
    services.AddScoped<IEventRepository, EventRepository>();           
}

您忘记在启动ConfigureServices方法中添加“services.AddScoped” 。

Answer 5

只有当有人和我一样的情况时,我才会使用现有数据库进行EntityFramework教程,但是当在模型文件夹上创建新的数据库上下文时,我们需要在启动时更新上下文,但不仅仅是在服务中.如果您有用户身份验证,则AddDbContext但AddIdentity也是如此

services.AddDbContext<NewDBContext>(options =>
                options.UseSqlServer(Configuration.GetConnectionString("DefaultConnection")));

services.AddIdentity<ApplicationUser, IdentityRole>()
                .AddEntityFrameworkStores<NewDBContext>()
                .AddDefaultTokenProviders();

Answer 6

我遇到了另一个问题，是的，已经为控制器的参数化构造函数添加了正确的接口。我所做的事情很简单。我只是去我的startup.cs文件，在那里我可以看到注册方法的调用。

public void ConfigureServices(IServiceCollection services)
{
   services.Register();
}

就我而言，此Register方法位于单独的类中Injector。因此，我不得不在其中添加新引入的接口。

public static class Injector
{
    public static void Register(this IServiceCollection services)
    {
        services.AddTransient<IUserService, UserService>();
        services.AddTransient<IUserDataService, UserDataService>();
    }
}

如果看到，此函数的参数为 this IServiceCollection

希望这可以帮助。

Answer 7

就我而言，Startup.cs 中的 .Net Core 3.0 API，在方法中

public void ConfigureServices(IServiceCollection services)

我不得不添加

services.AddScoped<IStateService, StateService>();

Answer 8

对于.NET 6.0

我只是在 Program.cs 上添加这一行

builder.Services.AddDbContext<DatabaseContext>();

Answer 9

您需要DBcontext在启动时添加新服务

默认

services.AddDbContext<ApplicationDbContext>(options =>
                options.UseSqlServer(
                    Configuration.GetConnectionString("DefaultConnection")));

加上这个

services.AddDbContext<NewDBContext>(options =>
                options.UseSqlServer(
                    Configuration.GetConnectionString("NewConnection")));

Answer 10

对我来说，它可以按如下方式添加数据库上下文ConfigureServices：

services.AddDBContext<DBContextVariable>();

Answer 11

由于一个很愚蠢的错误，我遇到了这个问题。我忘记了挂钩服务配置过程以在ASP.NET Core应用程序中自动发现控制器。

添加此方法可以解决该问题：

// Add framework services.
            services.AddMvc()
                    .AddControllersAsServices();      // <---- Super important

Answer 12

我必须在ConfigureServices中添加此行才能工作。

services.AddSingleton<IOrderService, OrderService>();

Answer 13

我低于异常

        System.InvalidOperationException: Unable to resolve service for type 'System.Func`1[IBlogContext]' 
        while attempting to activate 'BlogContextFactory'.\r\n at 
        Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteFactory.CreateArgumentCallSites(Type serviceType, Type implementationType, ISet`1 callSiteChain, ParameterInfo[] parameters, Boolean throwIfCallSiteNotFound)\r\n at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteFactory.CreateConstructorCallSite(Type serviceType, Type implementationType, ISet`1 callSiteChain)\r\n at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteFactory.TryCreateExact(ServiceDescriptor descriptor, Type serviceType, ISet`1 callSiteChain)\r\n at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteFactory.TryCreateExact(Type serviceType, ISet`1 callSiteChain)\r\n at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteFactory.CreateCallSite(Type serviceType, ISet`1 callSiteChain)\r\n at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteFactory.CreateArgumentCallSites(Type serviceType, Type implementationType, ISet`1 callSiteChain, ParameterInfo[] parameters, Boolean throwIfCallSiteNotFound)\r\n at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteFactory.CreateConstructorCallSite(Type serviceType, Type implementationType, ISet`1 callSiteChain)\r\n at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteFactory.TryCreateExact(ServiceDescriptor descriptor, Type serviceType, ISet`1 callSiteChain)\r\n at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteFactory.TryCreateExact(Type serviceType, ISet`1 callSiteChain)\r\n at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteFactory.CreateCallSite(Type serviceType, ISet`1 callSiteChain)\r\n at Microsoft.Extensions.DependencyInjection.ServiceProvider.CreateServiceAccessor(Type serviceType, ServiceProvider serviceProvider)\r\n at System.Collections.Concurrent.ConcurrentDictionaryExtensions.GetOrAdd[TKey, TValue, TArg] (ConcurrentDictionary`2 dictionary, TKey key, Func`3 valueFactory, TArg arg)\r\n at Microsoft.Extensions.DependencyInjection.ServiceProvider.GetService(Type serviceType)\r\n at Microsoft.Extensions.Internal.ActivatorUtilities.GetService(IServiceProvider sp, Type type, Type requiredBy, Boolean isDefaultParameterRequired)\r\n at lambda_method(Closure , IServiceProvider , Object[] )\r\n at Microsoft.AspNetCore.Mvc.Controllers.ControllerFactoryProvider.<>c__DisplayClass5_0.<CreateControllerFactory>g__CreateController|0(ControllerContext controllerContext)\r\n at Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker.Next(State& next, Scope& scope, Object& state, Boolean& isCompleted)\r\n at Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker.InvokeInnerFilterAsync()\r\n at Microsoft.AspNetCore.Mvc.Internal.ResourceInvoker.InvokeNextExceptionFilterAsync()

因为我想注册工厂来创建 DbContext 派生类 IBlogContextFactory 的实例并使用 Create 方法来实例化博客上下文的实例，以便我可以使用下面的模式以及依赖注入，还可以使用模拟进行单元测试。

我想使用的模式是

public async Task<List<Blog>> GetBlogsAsync()
        {
            using (var context = new BloggingContext())
            {
                return await context.Blogs.ToListAsync();
            }
        }

但不是 new BloggingContext() 我想通过构造函数注入工厂，如下面的 BlogController 类

    [Route("blogs/api/v1")]

public class BlogController : ControllerBase
{
    IBloggingContextFactory _bloggingContextFactory;

    public BlogController(IBloggingContextFactory bloggingContextFactory)
    {
        _bloggingContextFactory = bloggingContextFactory;
    }

    [HttpGet("blog/{id}")]
    public async Task<Blog> Get(int id)
    {
        //validation goes here 
        Blog blog = null;
        // Instantiage context only if needed and dispose immediately
        using (IBloggingContext context = _bloggingContextFactory.CreateContext())
        {
            blog = await context.Blogs.FindAsync(id);
        }
        //Do further processing without need of context.
        return blog;
    }
}

这是我的服务注册码

            services
            .AddDbContext<BloggingContext>()
            .AddTransient<IBloggingContext, BloggingContext>()
            .AddTransient<IBloggingContextFactory, BloggingContextFactory>();

以下是我的模型和工厂类

    public interface IBloggingContext : IDisposable
{
    DbSet<Blog> Blogs { get; set; }
    DbSet<Post> Posts { get; set; }
}

public class BloggingContext : DbContext, IBloggingContext
{
    public DbSet<Blog> Blogs { get; set; }
    public DbSet<Post> Posts { get; set; }

    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    {
        optionsBuilder.UseInMemoryDatabase("blogging.db");
        //optionsBuilder.UseSqlite("Data Source=blogging.db");
    }
}

public interface IBloggingContextFactory
{
    IBloggingContext CreateContext();
}

public class BloggingContextFactory : IBloggingContextFactory
{
    private Func<IBloggingContext> _contextCreator;
    public BloggingContextFactory(Func<IBloggingContext> contextCreator)// This is fine with .net and unity, this is treated as factory function, but creating problem in .netcore service provider
    {
        _contextCreator = contextCreator;
    }

    public IBloggingContext CreateContext()
    {
        return _contextCreator();
    }
}

public class Blog
{
    public Blog()
    {
        CreatedAt = DateTime.Now;
    }

    public Blog(int id, string url, string deletedBy) : this()
    {
        BlogId = id;
        Url = url;
        DeletedBy = deletedBy;
        if (!string.IsNullOrWhiteSpace(deletedBy))
        {
            DeletedAt = DateTime.Now;
        }
    }
    public int BlogId { get; set; }
    public string Url { get; set; }
    public DateTime CreatedAt { get; set; }
    public DateTime? DeletedAt { get; set; }
    public string DeletedBy { get; set; }
    public ICollection<Post> Posts { get; set; }

    public override string ToString()
    {
        return $"id:{BlogId} , Url:{Url} , CreatedAt : {CreatedAt}, DeletedBy : {DeletedBy}, DeletedAt: {DeletedAt}";
    }
}

public class Post
{
    public int PostId { get; set; }
    public string Title { get; set; }
    public string Content { get; set; }
    public int BlogId { get; set; }
    public Blog Blog { get; set; }
}

----- 为了在 .net Core MVC 项目中修复这个问题——我对依赖项注册做了以下更改

            services
            .AddDbContext<BloggingContext>()
            .AddTransient<IBloggingContext, BloggingContext>()
            .AddTransient<IBloggingContextFactory, BloggingContextFactory>(
                    sp => new BloggingContextFactory( () => sp.GetService<IBloggingContext>())
                );

简而言之，.net 核心开发人员负责注入工厂函数，在 Unity 和 .Net Framework 的情况下，它被处理了。