验证码与页面验证

在.NET中新建一个Web项目，添加一个.ASPX页面，取名VerifyCode.aspx, 转到其代码编辑状态，将下面的代码Copy&Paste过去就可以用了，有什么意见或问题欢迎提出^@^

using System;
using System.Collections;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Web;
using System.Web.SessionState;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.HtmlControls;
using System.Drawing.Imaging;
using System.Drawing.Text;

namespace VerifyCode
{
    /**//// <summary>
    /// 页面验证码程序
    /// 使用：在页面中加入HTML代码 <img src="VerifyCode.aspx">
    /// </summary>
    public class VerifyCode : System.Web.UI.Page
    {

        Private Members#region Private Members
        static string[] FontItems  = new string[] {   "Arial", 
                                                      "Helvetica", 
                                                      "Geneva", 
                                                      "sans-serif", 
                                                      "Verdana"
                                                  };

        static Brush[] BrushItems = new Brush[] {     Brushes.OliveDrab,
                                                      Brushes.ForestGreen,
                                                      Brushes.DarkCyan,
                                                      Brushes.LightSlateGray,
                                                      Brushes.RoyalBlue,
                                                      Brushes.SlateBlue,
                                                      Brushes.DarkViolet,
                                                      Brushes.MediumVioletRed,
                                                      Brushes.IndianRed,
                                                      Brushes.Firebrick,
                                                      Brushes.Chocolate,
                                                      Brushes.Peru,
                                                      Brushes.Goldenrod
                                                };

        static string[] BrushName = new string[] {    "OliveDrab",
                                                      "ForestGreen",
                                                      "DarkCyan",
                                                      "LightSlateGray",
                                                      "RoyalBlue",
                                                      "SlateBlue",
                                                      "DarkViolet",
                                                      "MediumVioletRed",
                                                      "IndianRed",
                                                      "Firebrick",
                                                      "Chocolate",
                                                      "Peru",
                                                      "Goldenrod"
                                                 };

        private static Color BackColor    =  Color.White;
        private static Pen   BorderColor  =  Pens.DarkGray;
        private static int   Width        =  52;
        private static int   Height       =  21;

        private Random _random;
        private string _code;
        private int    _brushNameIndex;
        #endregion // end of Private Members


        Web Form Designer generated code#region Web Form Designer generated code
        override protected void OnInit(EventArgs e)
        {
            //
            // CODEGEN: This call is required by the ASP.NET Web Form Designer.
            //
            InitializeComponent();
            base.OnInit(e);
        }
        
        /**//// <summary>
        /// Required method for Designer support - do not modify
        /// the contents of this method with the code editor.
        /// </summary>
        private void InitializeComponent()
        {    
            this.Load += new System.EventHandler(this.Page_Load);
        }
        #endregion


        PageLoad Event#region PageLoad Event
        public void Page_Load(object sender, System.EventArgs e)
        {
            //
            // TODO : initialize
            //
            this._random = new Random();
            this._code = GetRandomCode();

            //
            // TODO : use Session["code"] save the VerifyCode
            //
            Session["code"] = this._code;

            //
            // TODO : output Image
            //
            this.SetPageNoCache();
            this.OnPaint();
        }
        #endregion // end of PageLoad Event


        Helper Methods#region Helper Methods
        /**//// <summary>
        /// 设置页面不被缓存
        /// </summary>
        private void SetPageNoCache()
        {
            Response.Buffer = true;
            Response.ExpiresAbsolute = System.DateTime.Now.AddSeconds(-1);
            Response.Expires = 0;
            Response.CacheControl = "no-cache";
            Response.AppendHeader("Pragma","No-Cache");
        }

        /**//// <summary>
        /// 取得一个 4 位的随机码
        /// </summary>
        /// <returns></returns>
        private string GetRandomCode()
        {
            return Guid.NewGuid().ToString().Substring(0, 4);
        }

        /**//// <summary>
        /// 随机取一个字体
        /// </summary>
        /// <returns></returns>
        private Font GetFont()
        {
            int fontIndex = _random.Next(0, FontItems.Length);
            FontStyle fontStyle = GetFontStyle(_random.Next(0, 2));
            return new Font(FontItems[fontIndex], 12, fontStyle);
        }

        /**//// <summary>
        /// 取一个字体的样式
        /// </summary>
        /// <param name="index"></param>
        /// <returns></returns>
        private FontStyle GetFontStyle(int index)
        {
            switch (index)
            {
                case 0:
                    return FontStyle.Bold;
                case 1:
                    return FontStyle.Italic;
                default:
                    return FontStyle.Regular;
            }
        }

        /**//// <summary>
        /// 随机取一个笔刷
        /// </summary>
        /// <returns></returns>
        private Brush GetBrush()
        {
            int brushIndex = _random.Next(0, BrushItems.Length);
            _brushNameIndex = brushIndex;
            return BrushItems[brushIndex];
        }
        #endregion // end of Helper Methods


        Paint Methods#region Paint Methods
        /**//// <summary>
        /// 绘画事件
        /// </summary>
        private void OnPaint()
        {
            Bitmap objBitmap = null;
            Graphics g = null;

            try
            {
                objBitmap = new Bitmap(Width, Height);
                g = Graphics.FromImage(objBitmap);

                Paint_Background(g);
                Paint_Text(g);
                Paint_TextStain(objBitmap);
                Paint_Border(g);

                objBitmap.Save(Response.OutputStream, ImageFormat.Gif);
                Response.ContentType = "image/gif";
            }
            catch {}
            finally
            {
                if (null != objBitmap)
                    objBitmap.Dispose();
                if (null != g)
                    g.Dispose();
            }
        }

        /**//// <summary>
        /// 绘画背景颜色
        /// </summary>
        /// <param name="g"></param>
        private void Paint_Background(Graphics g)
        {
            g.Clear(BackColor);
        }

        /**//// <summary>
        /// 绘画边框
        /// </summary>
        /// <param name="g"></param>
        private void Paint_Border(Graphics g)
        {
            g.DrawRectangle(BorderColor, 0, 0, Width - 1, Height - 1);
        }

        /**//// <summary>
        /// 绘画文字
        /// </summary>
        /// <param name="g"></param>
        private void Paint_Text(Graphics g)
        {
            g.DrawString(_code, GetFont(), GetBrush(), 3, 1);
        }

        /**//// <summary>
        /// 绘画文字噪音点
        /// </summary>
        /// <param name="g"></param>
        private void Paint_TextStain(Bitmap b)
        {
            for (int n=0; n<30; n++)
            {
                int x = _random.Next(Width);
                int y = _random.Next(Height);
                b.SetPixel(x, y, Color.FromName(BrushName[_brushNameIndex]));
            }
        }
        #endregion // end of Paint Methods


    } // end of class

} // end of namespace