Unity:无法从不同的程序集注册类型

Question

我正在尝试Dependency injection在我的MVC应用程序中实现.我正在使用Unity.Mvc3.dllIoC.我只是想知道Unity如何不能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控制器中的用法:

[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 消息正常时,它始终为null.

这是PlayerService班级

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();
    }
}

这是完整的错误消息

依赖项的解析失败,type ="System.Web.Mvc.IControllerFactory",name ="(none)".
在解决时发生异常:
异常是:InvalidOperationException - 当前类型System.Web.Mvc.IControllerFactory是一个接口,无法构造.你错过了类型映射吗？

Answer 1

您正在隐藏所有异常并catch { return null; }尝试删除它,并查看解析时抛出的异常.我认为PlayerService构造函数中抛出了异常.

编辑:

来自http://mvchosting.asphostcentral.com/post/ASPNET-MVC-3-Hosting-Problem-in-implementing-IControllerActivator-in-ASPNET-MVC-3.aspx

当MVC应用程序第一次启动时,将按以下顺序使用以下类型调用依赖项解析程序:

• IControllerFactory
• IControllerActivator
• HomeController的

如果没有注册类型,如果你没有实现你的解析器返回null,那么你可能最终会看到类似于的错误:

当前类型System.Web.Mvc.IControllerFactory是一个接口,无法构造

Answer 2

默认情况下,unity选择具有最多参数的构造函数,因此我认为它将尝试使用dbContext参数的第二个构造函数,它无法解析.如果使用属性[InjectionConstructor]标记默认构造函数,那么希望这将解决您的问题