using System;
using System.Collections.Generic;
using
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;

namespace basicgraphic
{
    public partial class frmMain : Form
    {
        int fg;
        public frmMain()
        {
            InitializeComponent();
        }

        private void btnClear_Click(object sender, EventArgs e)
        {
            fg = 0;
            this.Invalidate();
        }
        private void btnCir_Click(object sender, EventArgs e)
        {
            fg = 1;
            this.Invalidate();
        }
        private void btnEllipse_Click(object sender, EventArgs e)
        {

            fg = 2;
            this.Invalidate();
        }
        private void btnPie_Click(object sender, EventArgs e)
        {

            fg = 3;
            this.Invalidate();
        }

        private void btnLine_Click(object sender, EventArgs e)
        {

            fg = 4;
            this.Invalidate();
        }

        private void btnArc_Click(object sender, EventArgs e)
        {

            fg = 5;
            this.Invalidate();
        }

        private void btn_Click(object sender, EventArgs e)
        {

            fg = 6;
            this.Invalidate();
        }

        private void panel1_Paint(object sender, PaintEventArgs e)
        {
            Graphics g = this.CreateGraphics();
            Pen pen1 = new Pen(Color.Blue, 3);
            switch (fg)
            {
                case 0:
                    g.Clear(Color.Gainsboro);
                    break;
                case 1:
                    g.DrawEllipse(pen1, 50, 50, 150, 150);
                    break;

                case 2:
                    g.DrawEllipse(pen1, 50, 50, 300, 200);
                    break;
                case 3:
                    g.DrawLine(pen1, 50, 100, 300, 100);
                    break;
                case 4:
                    g.DrawArc(pen1, 50, 50, 200, 300, 180, 90);
                    break;
                case 5:
                    g.DrawRectangle(pen1, 50, 50, 200, 150);
                    break;
                case 6:
                    g.DrawPie(pen1, 100, 100, 300, 200, 225, 90);
                    break;
            }
        }
    }
}
windows应用程序 7个Button 1.btnClear  清除2.btnCir 圆 3.btnEllipse 椭圆 4.benPie扇形   5.btnLine 直线6.btnArc弧线 7.btn矩形  
还有我自己加了个panel..书本没的！还有private void panel1_Paint(object sender, PaintEventArgs e) 书本这句是
private void femMain_Paint(object sender, PaintEventArgs e)
生成成功..却运行不出图像！点解！

Graphics g = this.panel1.CreateGraphics();

this.Invalidate();
这调用的什么啊，没见过这个函数

这个就只是个控制台应用程序呀

            Graphics g = e.Graphics;
or :
            Graphics g = panel1.CreateGraphics();

basicgraphic frmMain 并不包含Pen1

这两个句子貌似不能同时用！e重哪里来的！

如果是在Form上绘图
Graphics g = this.CreateGraphics();
如果在Panel1上绘图
Graphics g = this.Panel1.CreateGraphics();

using System;
using System.Collections.Generic;
using  System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace basicgraphic
{
    public partial class Form1 : Form
    {
        int fg=1;
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
           
            if (fg >= 6)'这里仅作测试之用
            {
                fg = 0;
            }
            else
            {
                fg = fg + 1;
            }
            this.panel1.Invalidate();'这个很关键：触发panel1的无效，让其重画

        }

        private void panel1_Paint(object sender, PaintEventArgs e)
        {
            Graphics g = this.panel1.CreateGraphics();'这里也是比较重要的
            Pen pen1 = new Pen(Color.Blue, 3);
            switch (fg)
            {
                case 0:
                    g.Clear(Color.Gainsboro);
                    break;
                case 1:
                    g.DrawEllipse(pen1, 50, 50, 150, 150);
                    break;

                case 2:
                    g.DrawEllipse(pen1, 50, 50, 300, 200);
                    break;
                case 3:
                    g.DrawLine(pen1, 50, 100, 300, 100);
                    break;
                case 4:
                    g.DrawArc(pen1, 50, 50, 200, 300, 180, 90);
                    break;
                case 5:
                    g.DrawRectangle(pen1, 50, 50, 200, 150);
                    break;
                case 6:
                    g.DrawPie(pen1, 100, 100, 300, 200, 225, 90);
                    break;
            }

        }
    }
}

            Graphics g = e.Graphics;
      or :
            Graphics g = panel1.CreateGraphics();
当然不能同时用了，所以 我写了 " or:" .

e 是事件→  private void panel1_Paint(object sender, PaintEventArgs e);