Unity:当前类型是接口，无法构造 [英] Unity: The current type is an interface and cannot be constructed

问题描述

从下面的代码开始

public interface IDataContextAsync : IDataContext
{
    Task<int> SaveChangesAsync(CancellationToken cancellationToken);
    Task<int> SaveChangesAsync();
}

public partial class DB1Context : DataContext{ }

public partial class DB2Context : DataContext{ }

下面是UnityConfig文件.注意:我正在为ASP.Net MVC使用Nuget引导程序，以下是我的UnityConfig文件

Below is the UnityConfig file. Note: I am using Nuget bootstrapper for ASP.Net MVC and below is my UnityConfig file

        public static void RegisterTypes(IUnityContainer container)
    {           
        container
            .RegisterType<IDataContextAsync, DB1Context>("DB1Context", new PerRequestLifetimeManager())
            //.RegisterType<IDataContextAsync, DB2Context>("DB2Context", new PerRequestLifetimeManager())
            .RegisterType<IRepositoryProvider, RepositoryProvider>(
                new PerRequestLifetimeManager(),
                new InjectionConstructor(new object[] {new RepositoryFactories()})
            )
            .
            .
            .
            .
    }

我得到以下错误:

当前类型Repository.Pattern.DataContext.IDataContextAsync为 接口，无法构造.您是否想念一种类型 映射?

The current type, Repository.Pattern.DataContext.IDataContextAsync, is an interface and cannot be constructed. Are you missing a type mapping?

了解此命名实例不适用于我的UnityConfig. 有想法的人吗?

Understand that this named instances is not working with my UnityConfig. Any idea guys?

预先感谢

推荐答案

正在执行解析的服务定位器(在构造函数要求IDataContextAsync之后)可能正在尝试这样解决:

Your service locator that is doing the resolving (after your constructor asks for IDataContextAsync) is probably trying to resolve like this:

Current.Resolve<IDataContextAsync>()

何时需要这样解决

Current.Resolve<IDataContextAsync>("DB1Context");

而且它不会内置任何额外的逻辑.

and there wouldn't be any extra logic built into it for it to know that.

如果要有条件解决，可以使用注射工厂:

If you want to conditionally resolve you could use an injection factory:

   public static class Factory
   {
        public static IDataContextAsync GetDataContext()
        {
            if (DateTime.Now.Hour > 10)
            {
                return new DB1Context();
            }
            else
            {
                return new DB2Context();
            }
        }
    }

..并像这样注册IDataContextAsync:

..and register IDataContextAsync like this:

Current.RegisterType<IDataContextAsync>(new InjectionFactory(c => Factory.GetDataContext()));

由于需要委托，因此您不一定需要静态类/方法，而是可以内联地完成它.

Since it takes a delegate you don't necessarily need the static class / method and could do it inline.

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