定义一个类，类中包含适当的属性和一个方法，该方法的参数为点的坐标值，当有一个点时，该方法划一个点；当有
两个点时，在两点中间画一条直线；当有三个点时，画一个三角形。


望大家给个全代码，我仔细琢磨，还不懂的我会续贴的。
一直在C板块逛的，来学习C#，忘大家指教。

那在那个类中定义三个方法，都用point来做参数不得了，还纠结什么?

你要的类如下

class Drawer
    {
        private List<Point> pointGroup = new List<Point>();
        private System.Drawing.Graphics graphics;
        private System.Windows.Forms.Control control;
        public Drawer(System.Windows.Forms.Control control)
        {
            this.control = control;
            graphics = control.CreateGraphics();
        }

        public void Draw(int x, int y)
        {
            if (pointGroup.Count == 3)
            {
                pointGroup.Clear();
                control.Refresh();
            }
            Point p = new Point(x, y);
            Size size = new Size(1, 1);
            Pen pen = new Pen(System.Drawing.Brushes.Black);
            Rectangle rect = new System.Drawing.Rectangle(p, size);
            pointGroup.Add(p);
            if (pointGroup.Count == 1)
            {
                graphics.DrawEllipse(pen, rect);
            }
            else if (pointGroup.Count == 2)
            {
                graphics.DrawEllipse(pen, rect);
                graphics.DrawLine(pen, pointGroup[0], pointGroup[1]);
            }
            else if (pointGroup.Count == 3)
            {
                graphics.DrawEllipse(pen, rect);
                graphics.DrawLine(pen, pointGroup[1], p);
                graphics.DrawLine(pen, pointGroup[0], p);
            }
        }
    }

 

using System.Drawing;
using System.Windows.Forms;

namespace Test
{
    class MyPointPaint:Panel
    {
        
        private Point[] P;

        // p 为坐标集合
        public MyPointPaint(Point[] p):base()
        {
            this.P = p;
            this.Size = new Size(new Point(400, 400));
        }

        // 绘制
        protected override void OnPaint(PaintEventArgs e)
        {
            if (this.P.Length < 1) 
                return;
            base.OnPaint(e);
            Graphics g = e.Graphics;
            Pen pen =new Pen(SystemBrushes.GrayText);
            if (this.P.Length == 3)
            {
                g.DrawPolygon(pen, this.P); // 绘制三角形
            }
            else if (this.P.Length == 1)
            {
                g.DrawEllipse(pen, new Rectangle(this.P[0].X, this.P[0].Y, 2, 2)); //  绘制一个圆点
            }
            else if (this.P.Length == 2)
            {
                g.DrawLine(pen, this.P[0], this.P[1]); // 绘制一条直线
            }
            else
            {
                g.DrawLines(pen, this.P); // 绘制所有坐标结构的线段
            }
            g.Flush();
        }
        
    }
}

// Test code
Point p1 = new Point(100, 100);
            Point p2 = new Point(200, 200);
            Point p3 = new Point(300, 150);
            Point[] ps = new Point[3];
            ps[0] = p1;
            ps[1] = p2;
            ps[2] = p3;
            MyPointPaint pp = new MyPointPaint(ps);
            this.Controls.Add(pp);

就是不会才问啊。不然你以为我想问啊。

我可以说我看不懂么？这道题目是多态，事件和借口 这部分的内容。有那么复杂么？

这个看不懂，那还是建议你去补习下GDI+吧！

谢谢忠告，我刚学的C#。你说的什么也不知道是什么，我会去问度娘的