.NET 具有不同服务实现的库中的核心依赖注入

Question

I have a library that configures dependency injection for another library (via IServiceCollection extension). However, that other library requires a different implementation of a service that is already registered in the application that will be using it even though only one implementation of that service is expected in the application.

Ie, Application relies on Service A with implementation A1 and Service B (from a separate library) that relies on Service A with implementation A2. Both implementations A1 and A2 come from libraries and are internal (registered using library-specific IServiceCollection extensions).

What is the way to make this work without exposing internal classes or changing the service implementation used by the application?

Answer 1

Register the service in the library that you have access to as a concrete type.

So that the services are registered like this:

services.AddTransient<ServiceA>();
services.AddTransient<IService, ServiceB>();

Then just refer to them like this:

public class ClassThatNeedsServiceA
{
    private ServiceA _serviceA;
    
    public ClassThatNeedsServiceA(ServiceA serviceA)
    {
        _serviceA = serviceA;
    }
}

public class ClassThatNeedsServiceB
{
    private ServiceB _serviceB;
    
    public ClassThatNeedsServiceA(IService serviceB)
    {
        _serviceB = serviceB;
    }
}

This will allow both services to be accessed correctly where needed.

If the new library needs to expose access to ServiceA and or ServiceB externally then it might be an indication that they should not be internal.