Call a method in child of child class

Question

I have three classes. First of them is abstract, and it is inherited by child class, which is again inherited. How to call method from the third class in abstract one?

Example code:

public abstract class DoSth
{
    public void DoSomething()
    {
        Console.WriteLine("I'm doing something");
        this.DoSomethingBigger();
    }
    protected abstract void DoSomethingBigger();
}

public class Writer : DoSth
{
    protected override void DoSomethingBigger()
    {
        Console.WriteLine("I'm writting");
    }
}

public class BookWriter : Writer
{
    protected new void DoSomethingBigger()
    {
        Console.WriteLine("I'm writting a book");
    }
}

How to call DoSomethingBigger() from a BookWriter class? When I make an instance of a BookWriter and I call DoSomething() my output is

I'm doing something
I'm writting

but I want

I'm doing something
I'm writting a book

You are not overriding the method in the 3rd class, you are basically creating an entirely new method that the base knows nothing about. Did you mean to override it instead? — DavidG, Jul 28 '18 at 15:18
Possible duplicate of [Confused about "override" vs. "new" in C#](https://stackoverflow.com/questions/2952887/confused-about-override-vs-new-in-c-sharp) — Camilo Terevinto, Jul 28 '18 at 16:59

Pavel Levchuk · Answer 1 · 2018-07-28T15:26:44.693

2

By marking your DoSomethingBigger method with new keyword you hide the initial DoSomethingBigger method instead of overriding it.

You should rewrite your code this way for it to work

public abstract class DoSth
{
    public void DoSomething()
    {
        Console.WriteLine("I'm doing something");
        this.DoSomethingBigger();
    }
    protected abstract void DoSomethingBigger();
}

public class Writer : DoSth
{
    protected override void DoSomethingBigger()
    {
        Console.WriteLine("I'm writting");
    }
}

public class BookWriter : Writer
{
    protected override void DoSomethingBigger()
    {
        Console.WriteLine("I'm writting a book");
    }
}

edited Jul 28 '18 at 15:26

answered Jul 28 '18 at 15:20

Pavel Levchuk

757
8
11

2

@Pavel You cannot have `virtual` and `override` in the same method signature. This code doesn't compile. – DavidG Jul 28 '18 at 15:23
Nice to hear that :) – Pavel Levchuk Jul 28 '18 at 15:24

score 2 · Accepted Answer · answered Jul 28 '18 at 15:21

2

You are not overriding the method in the 3rd class, you are basically creating an entirely new method that the base knows nothing about. see here for more info. It's no different than changing the name of the method in BookWriter to something completely different like DoSomethingElseAltogether(), now it's much more obvious that you cannot call it from the base class.

Instead, you should override in the third class:

public class BookWriter : Writer
{
    protected override void DoSomethingBigger()
    {
        Console.WriteLine("I'm writting a book");
    }
}

answered Jul 28 '18 at 15:21

DavidG

113,891
12
217
223

might I add that you probably want to `base.DoSomething()` to ensure it does what's in the superclass too – ScottishTapWater Jul 28 '18 at 15:26
1

@Persistence Well maybe, depends on your use case. OP doesn't have it in the middle class, and if they did, I don't think it's what is required here. – DavidG Jul 28 '18 at 15:28

Call a method in child of child class

2 Answers2