C＃在省略号之间绘制线条

Question

我正在制作一个程序，涉及在给定的“省略号”之间绘制线条。当我尝试运行模拟器，并且鼠标进入第一个“椭圆”时，我得到一个异常处理问题，将椭圆投射到点。如果推荐的话我可以用不同的方式做，我只需要能够在给定的坐标之间绘制一条线，每个坐标都与相应的椭圆相关。帮助

    Point old;
    List<String> DrawnLines = new List<String>();
    private void CheckPoint(object sender, System.Windows.Input.MouseEventArgs e)
    {

        Point selectedEllipse = (Point)sender;


        if (old.Equals(null))
        {
            old.Equals(sender);
        }
        else
        {
            if (selectedEllipse.Equals(old) == false) 
    //This is a check to make sure that a different point has been hit
            {
                System.Windows.Shapes.Line connectline = new System.Windows.Shapes.Line();
                connectline.Width = 10;
                connectline.X1 = old.X;
                connectline.Y1 = old.Y;
                connectline.X2 = selectedEllipse.X; //.Margin.Left;
                connectline.Y2 = selectedEllipse.Y; //.Margin.Top;
                drawCanvas.Children.Add(connectline);
                DrawnLines.Add((old.ToString() + " " + selectedEllipse.ToString()));
                DrawnLines.Add((selectedEllipse.ToString() + " " + old.ToString()));
                old = (Point)sender;
            }
        }
    }