多态性C#随机形状

我正在努力做一个在C#书中找到的练习。该练习以继承和多态性为基础，并以Shapes为例。这个概念是在GUI中插入一个数字，这个数字被输入，三个形状的随机组合将出现在屏幕上。

现在，我已经达到了每次点击都可以获得随机形状的程度，比如说，如果输入数字5，我会得到5个相同形状的实例。

目标是尝试获得三种不同类型形状的随机组合，这样，如果传入5，您可能会得到2个圆、1个正方形和1个斑点圆。

我已经尝试过调试程序，但我很难理解为什么在DrawShapes方法的每次迭代中都没有调用我的Shape方法，而每次执行只调用一次。我已经在下面发布了我的解决方案中的相关代码。如有任何帮助，我们将不胜感激。谢谢

画布类

    public void DrawShapes(int numberOfShapes)
    {
        if (numberOfShapes < 0)
        {
            throw new ArgumentOutOfRangeException();
        }
        var randomVariable = new Random();
        for (var i = 0; i < numberOfShapes; i++)
        {
            var x = randomVariable.Next(0, this.canvas.Width - sizeOfLargestShape);
            var y = randomVariable.Next(0, this.canvas.Height - sizeOfLargestShape);
            this.newShape = new Shape(x, y);
            this.listOfShapes.Add(this.newShape);
        }
    } 

形状类

    private Shape()
    {
        this.randomShape = new RandomShape();
        this.newShapeType = this.randomShape.GetUniqueShape(this);
        this.randomNumber = new Random();
    }
    public Shape(Point location) : this()
    {
        this.point = location;
    }
    public Shape(int x, int y) : this()
    {
        this.point = new Point(x, y);
    }

随机形状类

    public ShapeType GetUniqueShape(Shape myShape)
    {
        this.square = new SquareShape(myShape);
        this.circle = new CircleShape(myShape);
        this.speckledCircle = new SpeckledCircleShape(myShape);
        this.listOfAllShapeTypes = new List<ShapeType>
        {
           this.square,
           this.circle,
           this.speckledCircle
        };
        this.randomInt = this.myRandom.Next(0, 2);
        return this.listOfAllShapeTypes[this.randomInt];
    }

Shape myShape = null;
switch (myRandom.Next(0, 3))
{
    case 0:
        myShape = new Square();
        break;
    case 1:
        myShape = new Circle();
        break;
    case 2:
        myShape = new SpeckledCircle();
        break;
}