c# - 统一: Cannot register type from different assembly

Question

我正在尝试在我的 MVC 应用程序中实现 Dependency injection。我正在为 IoC 使用 Unity.Mvc3.dll。我只是想知道 Unity 如何无法从另一个程序集中注册类型。这是代码:

protected void Application_Start()
{
    AreaRegistration.RegisterAllAreas();

    RegisterGlobalFilters(GlobalFilters.Filters);
    RegisterRoutes(RouteTable.Routes);

    var container = new UnityContainer();

    // ok: register type from this assembly
    container.RegisterType<IMessages, Messages>();

    // fail: register type from another assembly (service reference)
    container.RegisterType<IPlayerService, PlayerService>();

    DependencyResolver.SetResolver(new UnityDependencyResolver(container));
}

public class UnityDependencyResolver : IDependencyResolver
{
    private readonly IUnityContainer _container;

    public UnityDependencyResolver(IUnityContainer container)
    {
        this._container = container;
    }

    public object GetService(Type serviceType)
    {
        try
        {
            return _container.Resolve(serviceType);
        }
        catch (Exception ex)
        {
            throw ex;
        }
    }

    public IEnumerable<object> GetServices(Type serviceType)
    {
        try
        {
            return _container.ResolveAll(serviceType);
        }
        catch (Exception ex)
        {
            throw ex;
        }
    }
}

在 MVC Controller 中的用法:

[Dependency]
public IPlayerService PlayerService { get; set; }

[Dependency]
public IMessages Messages { get; set; }


public ActionResult Index()
{
    PlayerMessageViewModel vm = new PlayerMessageViewModel();
    vm.Messages = Messages; // success!
    vm.Players = PlayerService.Get(); // fail: null reference exception :PlayerService

    return View(vm);
}

PlayerService 在 Messages 正常时始终为 null。

这是 PlayerService 类

public class PlayerService : IPlayerService
{
    private readonly MyDbEntities _dbContext;

    public PlayerService()
    {
        _dbContext = new MyDbEntities();
    }

    public PlayerService(MyDbEntities dbContext)
    {
        _dbContext = dbContext;
    }


    public IQueryable<Player> Get()
    {
        return _dbContext.Players.AsQueryable();
    }
}

这是完整的错误信息

Resolution of the dependency failed, type = "System.Web.Mvc.IControllerFactory", name = "(none)".
Exception occurred while: while resolving.
Exception is: InvalidOperationException - The current type, System.Web.Mvc.IControllerFactory, is an interface and cannot be constructed. Are you missing a type mapping?

Answer 1

默认情况下，unity 会选择参数最多的构造函数，所以我认为它会尝试使用第二个构造函数和 dbContext 参数，它无法解析。如果您使用属性 [InjectionConstructor] 标记您的默认构造函数，那么希望这将解决您的问题