Question

I have two classes, A & B. B is inheriting from A, I want to inverse the dependency.

Class A { }

Class B : A { }

Class B is inheriting from A. It means B has some dependency from A.

What will be the correct way to inverse the dependency?

Answer 1

Inheritance is a concept implying tight coupling between classes.

In order to use Dependency Injection you need to create some “Seams”, as Michael Feathers calls them in Working Effectively with Legacy Code. Here you can find a definition of Seam:

A seam is a place where you can alter behavior in your program without
editing in that place.

When you have a seam, you have a place where behavior can change.

By this definition, there is no Seam in your example, which is not necessarily a bad thing. The question is now, why do you feel the need to do Dependency Injection in this place?

If it’s for the sake of example, don’t do Dependency Injection here. There are places where it does not really make sense to apply it: if you have no volatility, why would you do it?

If you do really feel the need to do something similar in your project though, you probably want to decouple the volatile concepts out of your inheritance hierarchy and create a Seam for these parts: you could have an interface to abstract these concepts, which at this point can be effectively injected into your client class.