强制执行显式接口

Question

Imagine we have an interface IFoo :

interface IFoo {
    void DoSomething();
}

Now we have an implementing class which calls this method within its constructor:

class MyBase : IFoo {

    MyBase() { this.DoSomething(); }

    void DoSomething() { /* ... */ }
}

Finally we have a class that inherits MyBase but shell provide another implementaion of the interface IFoo . But when debugging I realise that constructor only accesses the implemetation on MyBase which I understand. Do get the right implementation of the interface I could explicitly call the interface-method from within the constructor using ((IFoo) this).DoSomething();

class MyDerived : MyBase, IFoo {
    void DoSomething() { /* ... */ }
}

But how can I enforce that the method MUST be cast to that interface before using it? I know I can explicitly implement the interface within both classes, but who forces me to do so? So we finally come to something like: how can I force someone who inherits my class to explicitly implement my interface also?

EDIT: Another approach would be to make DoSomething virtual in MyBase and ommit the derived class from implementing IFoo . However I get R#-Warning on calling virtual member within constructor then.

Answer 1

This is what I would do, mark the method in base class as virtual so it can be overriden in the child class. The child class doesn't need to explicitly implement the interface because it is inheriting the parent's behaviour.

interface IFoo {
    void DoSomething();
}

class MyBase : IFoo {

    MyBase() { this.DoSomething(); }

    **virtual** void DoSomething() { /* ... */ }
}

class MyDerived : MyBase {
    **override** void DoSomething() { /* ... */ }
}