Enforce override method to base class

Question

I have the following code:

public partial class Root : ICustomInterface
{
    public virtual void Display()
    {
        Console.WriteLine("Root");
        Console.ReadLine();
    }
}
public class Child : Root
{
    public override void Display()
    {
        Console.WriteLine("Child");
        Console.ReadLine();
    }
}
class Program
{
    static void Main(string[] args)
    {
        Root temp;
        temp = new Root();
        temp.Display();
    }
}

Output: "Root"
Desired output: "Child"

When I instantiate a Root object and call the Display() method I want to display the overridden method in Child is this possible.

I need this because I must create a plugin that's an extension to the base code and voids the Display() method of the Root class and implements only the plugin's method Child

I don't think you fully understand inheritance. you need to create an instance of Child if you want the Display() method to output "Child" — Dave Lawrence, Apr 04 '13 at 09:11
For your edited part of question you should see : http://stackoverflow.com/questions/2779146/c-is-there-way-for-a-class-to-remove-methods-that-it-has-inherited and also this one: http://stackoverflow.com/questions/1125746/how-to-hide-remove-a-base-classs-methods-in-c — Habib, Apr 04 '13 at 09:25

score 6 · Answer 1 · answered Apr 04 '13 at 09:10

When I instantiate a Root object and call the Display() method I want to display the overridden method in Child is this possible.

You need to create instance of the Child class.

Root temp;
temp = new Child(); //here
temp.Display();

Currently your object temp is holding reference of the base class, it doesn't know anything about the child, hence the output from the base class.

score 2 · Answer 2 · answered Apr 04 '13 at 09:12

When I instantiate a Root object and call the Display() method I want to display the overridden method in Child is this possible.

No. Suppose you add another class:

public class Child2 : Root
{
    public override void Display()
    {
        Console.WriteLine("Child 2");
        Console.ReadLine();
    }
}

Then which method (Child.Display() or Child2.Display()) would you expect to be called for a Root instance?

score 1 · Answer 3 · answered Apr 04 '13 at 09:11

It is not possible with your current code because you are creating a Root instance and not a Child instance. Therefore it has no idea about the Display method inside Child.

You'll need to create a Child class:

Root temp;
temp = new Child();
temp.Display();

score 1 · Answer 4 · answered Apr 04 '13 at 09:11

1

This is not how OOP works. You cannot use an overridden method in a base class. If you do this:

static void Main(string[] args)
{
    Root temp;
    temp = new Child();
    temp.Display();
}

You should get your desired output.

answered Apr 04 '13 at 09:11

Elad Lachmi

10,406
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I don't want to modify the temp object. – XandrUu Apr 04 '13 at 09:13
2

Then you don't know what you're doing – Dave Lawrence Apr 04 '13 at 09:24

Fabio Marcolini · Accepted Answer · 2013-04-04T09:18:36.073

1

No it's not possible you have to instantiate a Child object instead of a root

Root temp;
temp = new Child();
temp.Display();

if you don't want to modify temp then you have to modify Root display method to print "child" instead of root

edited Apr 04 '13 at 09:18

answered Apr 04 '13 at 09:11

Fabio Marcolini

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I don't want to modify the temp object. – XandrUu Apr 04 '13 at 09:12
I don't want to do that I want to create a plugin and not modify the base code of the project, the plugin must be an extension that voids the Root method and calls only my Child method. – XandrUu Apr 04 '13 at 09:16
1

That's impossible, if the object is a Root and Root display "Root". How are you gonna modify the output if you can't modify the code? – Fabio Marcolini Apr 04 '13 at 09:19

Enforce override method to base class

5 Answers5