Autofac异常:无法解析构造函数'Void .ctor的参数 [英] Autofac Exception: Cannot resolve parameter of constructor 'Void .ctor

问题描述

我遇到以下错误:

ExceptionMessage =没有发现以下构造函数 类型上的"Autofac.Core.Activators.Reflection.DefaultConstructorFinder" 可以使用``RestAPI.DevelopersController''进行调用 服务和参数:无法解析参数 构造函数'Void'的'Services.DevelopersService userService' .ctor(Services.DevelopersService)".

ExceptionMessage=None of the constructors found with 'Autofac.Core.Activators.Reflection.DefaultConstructorFinder' on type 'RestAPI.DevelopersController' can be invoked with the available services and parameters: Cannot resolve parameter 'Services.DevelopersService userService' of constructor 'Void .ctor(Services.DevelopersService)'.

Global.asax.cs

protected void Application_Start()
    {
        GlobalConfiguration.Configure(WebApiConfig.Register);
        AutoMapperConfig.RegisterMappings();
        var builder = new ContainerBuilder();
        builder.RegisterModule(new ServiceModule());
        builder.RegisterModule(new ORMModule());
        builder.RegisterApiControllers(Assembly.GetExecutingAssembly()).PropertiesAutowired();
        var container = builder.Build();
        var resolver = new AutofacWebApiDependencyResolver(container);
        GlobalConfiguration.Configuration.DependencyResolver = resolver;
    }

ServiceModule.cs

public class ServiceModule : Autofac.Module
{
    protected override void Load(ContainerBuilder builder)
    {
        builder.RegisterAssemblyTypes(Assembly.Load("Services"))
                 .Where(t => t.Name.EndsWith("Service"))
                 .AsImplementedInterfaces()
                 .InstancePerLifetimeScope();
    }
}

ORMModule.cs

public class ORMModule : Autofac.Module
{
    protected override void Load(ContainerBuilder builder)
    {
        builder.RegisterType(typeof(DatabaseContext)).As(typeof(DbContext)).InstancePerLifetimeScope();
    }
}

DevelopersController

public class DevelopersController : ApiController
{
    private DevelopersService _developersService;

    public DevelopersController(DevelopersService userService)
    {
        _developersService = userService;
        _developersService.SetIdentity(HttpContext.Current.Request.LogonUserIdentity.Name.ToString().Substring(4));
    }

DevelopersService.cs

public class DevelopersService : IService<User>
{
    private DatabaseContext _db;

    public DevelopersService(DatabaseContext db)
    {
        _db = db;
    }

    public void SetIdentity(string username)
    {

    }

    public User Create(User entity)
    {
        return new User();
    }
    public User Read(User Id)
    {
        return new User();
    }
    public void Update(User user)
    {

    }
    public void Delete(User Id)
    {

    }
    public IEnumerable<User> GetAll()
    {
        return _db.Users.AsEnumerable();
    }
}

IService.cs

public interface IService<T> where T : BaseEntity
{
    void SetIdentity(string identity);
    T Create(T entity);
    T Read(T Id);
    void Update(T entity);
    void Delete(T Id);
    IEnumerable<T> GetAll();
}

我该如何解决?

推荐答案

当 Autofac 尝试实例化DevelopersController时，会出现此错误消息.为了创建一个新的DevelopersController，它必须提供一个实例DevelopersService，但是它们都没有在 Autofac 中注册.

This error message occurs when Autofac try to instantiate a DevelopersController. In order to create a new DevelopersController it have to provide an instance DevelopersService but none of them are registered in Autofac.

即使是以下代码段

builder.RegisterAssemblyTypes(Assembly.Load("Services"))
       .Where(t => t.Name.EndsWith("Service"))
       .AsImplementedInterfaces()
       .InstancePerLifetimeScope();

在 Autofac 中注册DevelopersService，它不会将其注册为DevelopersService，而是注册为已实现的接口(即IService<User>)

register a DevelopersService in Autofac, it doesn't register it as a DevelopersService but as implemented interfaces (ie IService<User>)

为了解决您的问题，您可以更改注册以将服务本身注册为

In order to fix your issue, you can change your registration to register the service as itself

builder.RegisterAssemblyTypes(Assembly.Load("Services"))
       .Where(t => t.Name.EndsWith("Service"))
       .AsImplementedInterfaces()
       .AsSelf()
       .InstancePerLifetimeScope();

或将您的DevelopersController更改为不依赖DevelopersService而是依赖IService<USer>

or change your DevelopersController to not rely on DevelopersService but on IService<USer>

public class DevelopersController : ApiController
{
    private IService<USer> _userService;

    public DevelopersController(IService<USer> userService)
    {
        _userService= userService;
        _userService.SetIdentity(HttpContext.Current.Request.LogonUserIdentity.Name.ToString().Substring(4));
    }

我会推荐这种解决方案.  

I would recommend this solution.  

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