配置 Unity 以解析构造函数参数和接口

Question

I have a FaxService class that takes two constructor parameters.

public FaxService(string phone, IFaxProvider faxProvider)

How is Unity configured to send a string for the first parameter and an IFaxProvider instance for the second? I realize I can inject another service that provides the string, but I am looking for a solution where I don't have to change the FaxService constructor parameters.

This is what I have so far...

class Program
{
    static void Main(string[] args)
    {
        var container = new UnityContainer();

        var phone = "214-123-4567";
        container.RegisterType<IFaxProvider, EFaxProvider>();
        container.RegisterType<IFaxService, FaxService>(phone);

        var fax = container.Resolve<IFaxService>();
    }
}

public interface IFaxService { }

public interface IFaxProvider { }

public class FaxService : IFaxService
{
    public FaxService(string phone, IFaxProvider faxProvider) { }
}

public class EFaxProvider : IFaxProvider { }

but it throws...

Unity.Exceptions.ResolutionFailedException HResult=0x80131500
Message=Resolution of the dependency failed, type = 'ConsoleApp3.IFaxService', name = '(none)'. Exception occurred while: while resolving.

Answer 1

var container = new UnityContainer();
var phone = "214-123-4567";
container.RegisterType<IFaxProvider, EFaxProvider>();
container.RegisterType<IFaxService, FaxService>(new InjectionConstructor(phone, typeof(IFaxProvider)));

var fax = container.Resolve<IFaxService>();

Answer 2

I am looking for a solution where I don't have to change the FaxService constructor parameters.

There is nothing built into Unity to do this without specifying at least the types of all constructor parameters.

var container = new UnityContainer();
var phone = "214-123-4567";
container.RegisterType<IFaxService, FaxService>(new InjectionConstructor(phone, typeof(IFaxProvider)));
container.RegisterType<IFaxProvider, EFaxProvider>();

var fax = container.Resolve<IFaxService>();

The list of parameters would need to change every time the constructor changes.

Workaround

If you don't want to change your DI registration if the constructor changes for FaxService , build an abstract factory to separate the string/primitive parameters from the services. Pass services through the constructor parameters of the factory. Pass string and primitive parameter types through the Build method parameters.

public class FaxServiceFactory
{
    private readonly IFaxProvider faxProvider;
    public FaxServiceFactory(IFaxProvider faxProvider)
    {
        this.faxProvider = faxProvider ?? throw new ArgumentNullException(nameof(faxProvider));
    }

    public IFaxService Create(string phone)
    {
        return new FaxService(phone, this.faxProvider);
    }
}

And then register like:

var container = new UnityContainer();

var phone = "214-123-4567";
container.RegisterType<FaxServiceFactory>();
container.RegisterType<IFaxProvider, EFaxProvider>();
container.RegisterInstance<IFaxService>(container.Resolve<FaxServiceFactory>().Create(phone));

var fax = container.Resolve<IFaxService>();

Another possibility is to use a DI container that allows you to specify partial lists of constructor parameters (Autofac, Ninject, StructureMap, and Castle Windsor all do this out of the box).