使用Unity在构造函数中解析同一接口的多个依赖项

Question

I am trying to resolve two dependencies on a single interface with two different implementations when creating a new object using Unity. I am using ASP.NET MVC 4 with a controller that has a number of dependencies I will recreate a dummy scenario below:

Say we have a controller that looks something like this:

public class HomeController : Controller
{
    public HomeController(IRepository repository, ISomeInterface someInterface1, ISomeInterface someInterface2, IConfiguration configuration)
    {
        // Code
    }
}

I need to be able to resolve ISomeInterface to two different classes and was hoping to do this based on name. Here is what I have so far which doesn't work in Boostrapper.cs:

var someInterface1 = new FirstImplementation();
var someInterface2 = new SecondImplementation();
container.RegisterInstance(typeof(ISomeInterface), someInterface1);
container.RegisterInstance(typeof(ISomeInterface), "someInterface2", someInterface2);

I have also had a look at this post but this didn't seem to solve my problem either: http://unity.codeplex.com/discussions/355192 I think this is solving a different problem to mine since I am trying to resolve 2 dependencies automatically in a constructor.

Any help with this problem would be appreciated, thanks

Answer 1

You could use Named registrations for that; in order to do so, register the types with a name (as you already did to a part in your sample):

var someInterface1 = new FirstImplementation();
var someInterface2 = new SecondImplementation();
container.RegisterInstance(typeof(ISomeInterface), "Impl1", someInterface1);
container.RegisterInstance(typeof(ISomeInterface), "Impl2", someInterface2);

You can then add a Dependency attribute to the parameter that you use to specify the relevant name:

public class HomeController : Controller
{
    public HomeController(IRepository repository, 
               [Dependency("Impl1")] ISomeInterface someInterface1, 
               [Dependency("Impl2")] ISomeInterface someInterface2, 
               IConfiguration configuration)
    {
        // Code
    }
}

For more information, see this link .

Answer 2

I think you'll be better to replace these two arguments ISomeInterface someInterface1, ISomeInterface someInterface2 with the only one which will get necessary implementations.

It could be some interface which inherited from IEnumerable<ISomeInterface> . This will allow you to enumerate all needed implementation.

public interface ISomeInterfaceEnumerator : IEnumerable<ISomeInterface>
{        
}

public class HomeController : Controller
{
    public HomeController(IRepository repository, ISomeInterfaceEnumerator someInterfaces, IConfiguration configuration)
    {
        // Code
    } 
}

Or maybe you can use more simple, but less flexible approach

public interface ISomeInterfaceInstances
{
    ISomeInterface someInterface1 { get; }
    ISomeInterface someInterface2 { get; }
}

public class HomeController : Controller
{
    public HomeController(IRepository repository, ISomeInterfaceInstances someInterfaces, IConfiguration configuration)
    {
        // Code
    } 
}

This is just idea, but implementation could be various