Question

I’d like to know if I follow the right path, because I feel that the following code is wrong. Sorry, I didn’t know how to name properly this question.

I have a certain ShapeEntity class that is used for loading data from DB. There are other concrete classes for Shape (I can have many of them in the future) so I want to employ LSP to draw these shapes, that’s why I use IShape abstraction. I instantiate concrete shape objects by using DB info which is provided by ShapeEntity.

So my concern lies inside Main() function where I create these Shapes just using simple if-else. Is this correct approach to create “unknown” objects using if-else block? Maybe I could carry out creation of Shape objects to some kind of ShapeService? How could it be solved the other way?

public class ShapeEntity
{
    int idShape { get; set; }
}

public interface IShape
{
    void Draw();
}

public class Square : IShape
{
    public void Draw() { }
}

public class Rectangle : IShape
{
    public void Draw() { }
}

public class Canvas()
{
    public static void Main()
    {
        List<IShape> Shapes = new List<IShape>();

        foreach(ShapeEntity ShapeItem in ShapeRepository.GetAll())
        {
            if(ShapeItem.idShape == 1)
            {
                Shapes.Add(new Square());
            }
            else if(ShapeItem.idShape == 2)
            {
                Shapes.Add(new Rectangle());
            }
        }
    }

    public void DrawShapesOnCanvas(IList<IShape> Shapes)
    {
        foreach(IShape Shape in Shapes)
        {
            Shape.Draw();
        }
    }
}

Answer 1

You should consider using Factory pattern and instead using Id you should use enum

Example:

 public class ShapeFactory
    {
        public static IShape GetShape(ShapeType shapeType)
        {
            switch (shapeType)
            {
                case ShapeType.Square:
                    return new Square();

                case ShapeType.Rectangle:
                    return new Rectangle();
                default:
                    break;
            }

            return null;
        }
    }

    public enum ShapeType
    {
        Square,
        Rectangle
    }