PRISM：RegisterType 给出隐式引用转换错误

Question

I have got three projects in my solution.

One holds the interface:

public interface ISetupData
{
    Dictionary<string, string> Data { get; set; } 
}

Another an implementation of the interface:

public class SetupData : ISetupData
{
    public Dictionary<string, string> Data { get; set; }
}

The third the uses both:

Container.RegisterType<ISetupData, SetupData>();

I have set the references in the projects so everything is recognised. But when i compile i get the error:

The type SetupData cannot be used as type parameter 'TTo' in the generic type or method 'Microsoft.Practices.Unity.UnityContainerExtensions.RegisterType(Microsoft.Practices.Unity.IUnityContainer, params Microsoft.Practices.Unity.InjectionMember[])'. There is no implicit reference conversion from SetupData to ISetupData.

If I put the declaration of the interface into the project of the implementation of the interface it works fine.

I don't have any idea what this error means. Can anyone help?

Answer 1

So I have the following, which works for me for getting report data out of my database context - I have simplified it to just the parts I think you might be interested in:

UnityConfig class

using System;
using Microsoft.Practices.Unity;
using WeeklyReport.Repository;
using System.Web.Mvc;
using Unity.Mvc3;

namespace WeeklyReport
{
    public class UnityConfig
    {
        public static void RegisterContainer()
        {
            var container = new UnityContainer();

            //ensure the repository is disposed after each request by using the lifetime manager
            container.RegisterType<IDataRepository, DataRepository>(new HierarchicalLifetimeManager());

            DependencyResolver.SetResolver(new UnityDependencyResolver(container));

        }
    }
}

IDataRepository class

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Mvc;
using WeeklyReport.Models;

namespace WeeklyReport.Repository
{
    public interface IDataRepository
    { 
        IEnumerable<ReportViewModel> GetAllMetrics();
    }
}

and my Repository class:

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

namespace WeeklyReport.Repository
{
    public class DataRepository : IDataRepository
    {
         // ....
         public IEnumerable<ReportViewModel> GetAllMetrics()
         {
             // ....
         }
    }
}

I then instantiate private readonly IDataRepository repository; in my Controller and I can call repository.GetAllMetrics() in my function that returns the data to my view.

Probably goes without saying, but hopefully you added the NuGet Package Unity .

I originally ran across the same error you did because I forgot to add : IDataRepository on my DataRepository class, meaning I was not inheriting the IDataRepository . I see that is not the problem in your case, but that is what the error means - it means the relationship is not established and the interface cannot find its underlying covariant ( ISetupData cannot find SetupData ).

I do not see that you created a UnityContainer , but are calling Container directly, instead. Probably not the best practice. And you would have needed to then do DependencyResolver.SetResolver(new UnityDependencyResolver(container)); . I would recommend creating an instance of the UnityContainer , not directly calling Container .

You said it worked when you "put the declaration of the interface into the project of the implementation of the interface"? Sorry, but that was EXTREMELY confusing and I have no idea what you meant by that.

I don't get why you are doing { get; set; } { get; set; } { get; set; } on both sides. One is supposed to be the implementation for the other, and you had Dictionary , not IDictionary . It should look like this:

public interface ISetupData
{
    IDictionary<string, string> Data;
}

After instantiating private readonly ISetupData myData; you should be able to use myData.Data to mean SetupData .

So I think if you use that, and do:

using System;
using Microsoft.Practices.Unity;
using WeeklyReport.Repository;
using System.Web.Mvc;
using Unity.Mvc3;

namespace WeeklyReport
{
    public class UnityConfig
    {
        public static void RegisterContainer()
        {
            var container = new UnityContainer();

            //ensure the repository is disposed after each request by using the lifetime manager
            container.RegisterType<ISetupData, SetupData>(new HierarchicalLifetimeManager());

            DependencyResolver.SetResolver(new UnityDependencyResolver(container));

        }
    }
}

You should've been fine, as long as your Global.ascx.cs had UnityConfig.RegisterContainer(); in the App_Start section.