Question

By way of an intro, I’m creating a basic Quadtree engine for personal learning purposes. I’m wanting this engine to have the capability of working with many different types of shapes (at the moment I’m going with circles and squares) that will all move around in a window and perform some sort of action when collision occurs.

After asking a question on the topic of generic lists earlier, I have decided on using an interface for polymorphism. The best interface for this would be an interface utilising Vector2 due to the fact that every object that appears in my Quadtree will have an x,y position and Vector2 covers that nicely. Here is my code as it currently stands:

public interface ISpatialNode {
    Vector2 position { get; set; }
}

public class QShape {
    public string colour { get; set; }
}

public class QCircle : QShape, ISpatialNode {
    public int radius;
    public Vector2 position {
        get { return position; }
        set { position = value; }
    }
    public QCircle(int theRadius, float theX, float theY, string theColour) {
        this.radius = theRadius;
        this.position = new Vector2(theX, theY);
        this.colour = theColour;
    }
}

public class QSquare : QShape, ISpatialNode {
    public int sideLength;
    public Vector2 position {
        get { return position; }
        set { position = value; }
    }
    public QSquare(int theSideLength, float theX, float theY, string theColour) {
        this.sideLength = theSideLength;
        this.position = new Vector2(theX, theY);
        this.colour = theColour;
    }
}

So I’ll be eventually wanting to have an interface that works to the point that I can use the generic list List<ISpatialNode> QObjectList = new List<ISpatialNode>(); and I can add shapes to it using the code QObjectList.Add(new QCircle(50, 400, 300, "Red")); or QObjectList.Add(new QSquare(100, 400, 300, "Blue")); or something along those lines (keep in mind that I’ll be wanting to add different shapes later along the line).

Problem is, this code doesn’t seem to work when I call it from here (Initialize() is the XNA method):

protected override void Initialize() {
    QObjectList.Add(new QCircle(5, 10, 10, "Red"));

    base.Initialize();
}

So my question has two parts:

1. Why does this code give me a stackoverflow error at the set {
position = value; } part of my QCircle and QSquare classes?

2. Would this be an efficient/effective way of utilising interfaces for
polymorphism?

Answer 1

Stack overflow is because:

public Vector2 position {
    get { return position; }
    set { position = value; }
}

the set actually sets the same again. You may want this:

private Vector2 _position;
public Vector2 position {
    get { return _position; }
    set { _position = value; }
}

or its short version:

public Vector2 position { get; set; } //BTW, the c# standard is to use upper camel case property names

Regarding the use of polymorphism, it seems right in this scenario.