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Simsons
Simsons

Reputation: 12745

How to invoke parent class method without creating object of it

I can invoke the parent class method by using base.virtualParentMethod(). But how do I call the method in parent-parent class without creating an object of it, in the following scenario.

 class A
    {
        public virtual void virtualParentMethod()
        {
            Console.WriteLine("A");
        }
    }
    class B : A
    {
        public override void virtualParentMethod()
        {
            Console.WriteLine("B");
        }
    }
    class C : B
    {
        public override void virtualParentMethod()
        {
            //base.virtualParentMethod();
            //This is where I want to invoke the method of A
            //So that out Will be : A
        }
    }

Upvotes: 1

Views: 16643

Answers (5)

RJ Lohan
RJ Lohan

Reputation: 6527

You've already created an instance of A, by creating an instance of C (as C : B, B : A), so there is a way you can do this with a small modification. Now, without indicating whether or not this is a good idea or not;

If you use the 'new' keyword instead of override on your derived method implementations, then you can call the base implementation of a method directly, bypassing the intermediate class implementation, by casting the object to the type who's implementation you want to use, like so;

class A
{
    public virtual void virtualParentMethod()
    {
        Console.WriteLine("A");
    }
}
class B : A
{
    public new void virtualParentMethod()
    {
        Console.WriteLine("B");
    }
}
class C : B
{
    public new void virtualParentMethod()
    {
        // casting this to A will allow you to call the base class implementation
        ((A)this).virtualParentMethod();
    }
}

Note that if you make this change, you've introduced a behavioural change to any callers of the method, depending on how they refer to the object. And if you try to cast in this way in the existing C.virtualParentMethod implementation (declared 'override'), you are really just calling the method itself and will get in an infinite loop.

Or, you could just reconsider your class design. :-)

Upvotes: 0

Sergey Berezovskiy
Sergey Berezovskiy

Reputation: 236328

If you need some parent functionality in not direct children of parent, then you should move that functionality to separate method:

class A
{
    public virtual void VirtualParentMethod()
    {
        Foo();
    }

    protected void Foo()
    {
        Console.WriteLine("A");
    }
}
class B : A
{
    public override void VirtualParentMethod()
    {
        Console.WriteLine("B");
    }
}
class C : B
{
    public override void VirtualParentMethod()
    {        
        Foo();
    }
}

UPDATE

Also consider:

  • inheriting C directly from A
  • changing inheritance order, i.e. B from C
  • extracting this behavior to other object

Upvotes: 4

Adam Houldsworth
Adam Houldsworth

Reputation: 64527

You cannot pick what version of a derived method to run using the base syntax. The only way to run a specific method would be to instantiate a version of A inside C that can be used for that method (basically, a real instance of A).

However I personally wouldn't do this. This is indicative of a design issue with your inheritance chain.

If you need to ensure that C runs A, why not inherit A from C - C : A.

Upvotes: 2

Rune FS
Rune FS

Reputation: 21752

You can't. using base.MethodName will always call the closest implementation up the hierachy and there's no way you can by pass this without explicitly declaring a method that can be called

it's also worth noting that if you find yourself in a situation where you wish to do this odds are you have a design flaw.

Upvotes: 0

Tigran
Tigran

Reputation: 62265

You simply can not, cause that is an essence of Virtual Method Table, so virtual keyword and its override. Invokation method's address will be lookuped from corresponding real type Virtual Methods Table.

Upvotes: 0

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