Question

Might look a silly question, but can I return an instance?
Example:

public class EcranJeu : AffichageJeu
{

    public EcranJeu(string choixecran)
    {
        if (choixecran == "0")
        {
            KystExtract décor = new KystExtract();
        }
        if (choixecran == "1")
        {
            KystExtraction décor = new KystExtraction();
        }
    }

    public override void  LoadContent()
    {
        décor.LoadContent(content);
    }
}

décor is said not to exist. How can I pass it to the LoadContent, Update and Draw of all the class?

Answer 1

The other answer was only partially correct as you found.

Problem: You are creating an object of one of two different classes and later want to call a LoadContent(), or Draw() or Update() method on the chosen object.

I have to assume the two classes KystExtract and KystExtraction have a common base class or share an interface. If not you will need to create/add one (e.g. KrystBase or IKryst) that defines the LoadContent() method.

The property you store is then of the base class type/interface, so it can hold either a KystExtract object or a KystExtraction object.

Your code will look like this (assuming you have no common base class and use an interface):

public class EcranJeu : AffichageJeu
{
    private IKystObject décor;  // for example
    public EcranJeu(string choixecran)
    {
        if (choixecran == "0")
        {
            décor = new KystExtract();
        }
        if (choixecran == "1")
        {
            décor = new KystExtraction();
        }
    }

    public override void  LoadContent()
    {
        décor.LoadContent(content);
    }
}

// Common interface for classes requiring shared behavior
public interface IKystObject
{
    public override void LoadContent();
    public override void Update();
    public override void Draw();
}

// Both classes implement your common interface
public class KystExtract : IKrystObject
{
    ... Implementation of LoadContent, Update and Draw
}

// Both classes implement your common interface
public class KystExtraction : IKrystObject
{
    ... Implementation of LoadContent, Update and Draw
}