c＃中的多级继承

Question

I am trying to call a method from class A and apply it to a value in class C:

class A
{
    //my code here
    public virtual string calculatebnft()
    {
        string bnft = "";
        //my code here
        return bnft;
    }
}

class B : A
{
    //my code here
    public override string calculatebnft()
    {
        string bnft = "";
        //my code here
        return bnft;
    }
}

class C : B
{
    //my code here
}

In my Main method:

C c1=new C();
//my code here
string bnft=c1.calculatebnft();
MessageBox.Show(bnft);

When I run program it always runs class B's method calculatebnft(). How can I call calculatebnft() from A instead? The rest of code from B "which is working correctly".

Answer 1

You can't do that without changing B code. You have to change calculatebnft method from override to new :

class B : A
{
    //my code here
    public new string calculatebnft()
    {
        string bnft = "";
        //my code here
        return bnft;
    }
}

with that you could do following:

string bngt = ((A)c1).calculatebnft();

Answer 2

From the outside there is no way to call a base class instance of a virtual method. It is simply not possible because it is forbidden by the CLR (possible, but not verifiable). The only way to get access to it is for A or B to give you another method on which to call the functionality. For example

class A {
  public string callMe() { 
   return ...;
  }

  public virtual string calculatebnft() {
    return callMe();
  }
}

Now a caller who wants the A version of calculatebnft can use callMe instead.

In general though I'd consider this bad practice. If there is a situation where you really wanted the base class version of a virtual method then it's probably not the best method to be virtual.

Answer 3

I don't think that's possible this way.

But for example you can do something like this:

class A
{
    //my code here
    public virtual string calculatebnft()
    {
        string bnft = "A";
        //my code here
        return bnft;
    }
}

class B : A
{
    public string calculatebnftFromA()
    {
        return base.calculatebnft();
    }

    //my code here
    public override string calculatebnft()
    {
        string bnft = "B";
        //my code here
        return bnft;
    }
}