Abstract Classes

Abstract Methods - Methods that must be overridden to create a concrete class.

Abstract classes can have abstract children, until all abstract methods have been overridden.

public abstract class Control
{
    protected int xPos;
    protected int yPos;

    public Control(
        int xPosition,
        int yPosition)
    {
        xPos = xPosition;
        yPos = yPosition
    } 

    public virtual void Clear()
    {
        Console.WriteLine(:"Clearing control");
    }

    //  Abstract Method
    public abstract void Draw();
}

class Button : Control
{
    private string text;

    public Button(
        int xPos,
        int yPox,
        string text) : base(xPos, yPos)
    {
        this.text = text;
    }

    public override void Draw()
    {
        Console.WriteLine("Drawing Button"); //  This Class is made concrete by overriding the abstract method.
    }

}

public class ListBox : Control
{
    private List<string> list = 
        new List<string>();

    public ListBox(
    int xPos,
    int yPos,
    List<string> contents) : 
        base(xPos, yPos)

    {
        this.list = contents;
    }

    public override void Draw();
    {
        Console.WriteLine("Listox Drawing");
    }
}

public class Worker
{
    public class Worker()
    {
        Work();
    }

    public void Work()
    {
        List<Control> controls = 
            new List<Control>();
        Button button = new Button(
            0, 100,
            "Click Me");
        ListBox listBox = new ListBox(
            100, 300, 
            new List<string>());
        Button cancelButton = new Button(
            150, 100,
            "cancel");

        controls.Add(button);
        controls.Add(listBox);
        controls.Add(cancelButton);

        foreach (Control control in controls)
        {
            control.Draw();
        }
    }
}