How do I specify constructor injections when there's several classes that implements an interface

Question

I want to use dependency injection for a class that takes an interface IService in its constructor. But I have several implementations of this interface. Both implementations are needed by other classes as well so I cannot simply only initiate the one needed. I'm using Microsoft.Extensions.DependencyInjection

Here's an example that tries to show my classes

public interface IService { }

public class ServiceA : IService { ... }

public class ServiceB : IService { ... }

public class Foo
{
    public Foo(IService service) { }
}

public class Bar
{
    public Bar(IService service)  { }
}

If I did not have several implementations I'd inject it like following:

builder.Services.AddSingleton<IService, ServiceA>();
builder.Services.AddSingleton<Foo>();

In the example I'd need Foo to be initialized with ServiceA and Bar to be initialized with ServiceB.

You will have to segregate your iterfaces further, so your hierachy will be as follows: `ServiceA->IServiceA->IService`. Then when registering you'll bind your Service to IServiceA instead of IService — Alex, Jul 23 '19 at 06:48

score 1 · Answer 1 · edited Jul 23 '19 at 08:55

1

Something like this (typing directly into the browser):

builder.Services.AddSingleton<ServiceA>();
builder.Services.AddSingleton<ServiceB>();
builder.Services.AddSingleton<Foo>(c =>
    ActivatorUtilities.CreateInstance<Foo>(c, c.GetRequiredService<ServiceA>())); 
builder.Services.AddSingleton<Bar>(c =>
    ActivatorUtilities.CreateInstance<Bar>(c, c.GetRequiredService<ServiceB>()));

edited Jul 23 '19 at 08:55

Steven

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answered Jul 23 '19 at 07:37

qujck

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How do I specify constructor injections when there's several classes that implements an interface

1 Answers1