CODEWITHSUNDEEP
c#inheritance
prologix
prologix

Reputation: 41

how to call derived function using base class object

class Parent
{
    public int GetNo()
    {
        return 1;
    }
}

class Child : Parent
{        
    public Child()
    {

    }

    public int GetNo()
    {                       
        return 2;
    }
}

Parent p = new Child();
p.GetNo();

But it calls Base.GetNo(). I know if I use virutal in base it will call Child.GetNo() But i can't use virutal in Base becuase i have to derive my class from base which is already distributed in DLL.So there's no way i can modify the existing functions of base class.

Any sugguestions are valued. Thanks

Upvotes: 4

Views: 8698

Answers (4)

deight
deight

Reputation: 391

I have just come here so i could find a solution that doesn't use casts, but since i didn't find it here is one.

Maybe it can be of help for someone.

abstract class Parent
{
    public int GetNo()
    {
        return GetNoImpl();
    }

    protected abstract int GetNoImpl();

}

class Child : Parent
{        
    public Child()
    {

    }

    protected override int GetNoImpl();
    {                       
        return 2;
    }
}

Parent p = new Child();
p.GetNo();

Note: the parent class is abstract.

Upvotes: 1

Petar Ivanov
Petar Ivanov

Reputation: 93090

You can cast it:

((Child)p).GetNo();

or

if(p is Child)
    (p as Child).GetNo();

Upvotes: 6

Matthew Abbott
Matthew Abbott

Reputation: 61617

Without virtual declared on the method, the base method will always be called because you declared your variable as Parent. If you can't append virtual to the base class, then you can only either declare the variable as Child, or cast it to Child and call your GetNo method:

Child p = new Child();
p.GetNo();

Or:

Parent p = new Child();
((Child)p).GetNo();

Upvotes: 0

RobV
RobV

Reputation: 28675

You can force this with an explicit cast e.g.

((Child)p).GetNo();

Or you can use hiding e.g.

public new int GetNo()
{
  return 2;
}

Though I think the latter only gets called if the variable is typed to the class that hides the method.

If you really need to override a method properly and it's from a compiled DLL consider getting in touch with the developers to see whether they can make the method virtual (and if not why) or if an open source project just get the source code and modify it yourself.

Upvotes: 0

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