圖形驗證碼的實作

• 作用：防止惡意注冊，惡意破解密碼，惡意灌水
• 分類：用戶端驗證和伺服器端驗證。
• 關鍵問題：1，獲得一個随機生成的字元串  2，把字元串畫到網頁上。  3.比較驗證

網上的代碼很多，自己也動手模仿了一個。

1. 獲得一個随機的字元串

 #region  随機取得數字字母

        private string GenarateCheckCode()

        {

            int number;

            char code;

            string checkCode = string.Empty;

            System.Random random = new Random();

            for (int i = 0; i <= 5; i++)

            {

                number = random.Next();

                if (number % 2 == 0)

                    code = (char)('0' + number % 10);

                else

                    code=(char)('A'+number%26);

                checkCode += code.ToString();

            }

            Session["num"] = checkCode;

            return checkCode;

        }

        #endregion

2.把字元串畫到網頁上

   #region 把随機數字和字母畫到圖檔上

        private void createCodeCheckImage(string checkCode)

        {

            if (checkCode == null || checkCode.Trim() == string.Empty)

                return;

            System.Drawing.Bitmap img = new Bitmap((Int32)Math.Ceiling(checkCode.Length*12.5),22);

            System.Drawing.Graphics g = Graphics.FromImage(img);

            try {

            Random random=new Random();

                g.Clear(Color.White);

                for(int i=0;i<25;i++)

                {

                     int x1=random.Next(img.Width);

                     int x2=random.Next(img.Width);

                     int y1=random.Next(img.Height);

                     int y2=random.Next(img.Height);

                    g.DrawLine(new Pen(Color.Silver),x1,y1,x2,y2);

                }

                Font font=new Font("Arial",12,FontStyle.Bold);

                System.Drawing.Drawing2D.LinearGradientBrush brush=new System.Drawing.Drawing2D.LinearGradientBrush(new Rectangle(0,0,img.Width,img.Height),Color.Blue,Color.Red,1.2f,true);

                g.DrawString(checkCode,font,brush,2,2);

                for(int i=0;i<10;i++)

                {

                   int x =random.Next(img.Width);

                    int y =random.Next(img.Height);

                    img.SetPixel(x,y,Color.FromArgb(random.Next()));

                }

                g.DrawRectangle(new Pen(Color.Silver),0,0,img.Width-1,img.Height-1);

                System.IO.MemoryStream ms=new System.IO.MemoryStream();

                img.Save(ms,System.Drawing.Imaging.ImageFormat.Gif);

                Response.ClearContent();

                Response.ContentType="image/Gif";

                Response.BinaryWrite(ms.ToArray());

            }

            finally{

                g.Dispose();

                img.Dispose();

            }

        }

        #endregion

3.驗證

private void checkCode() 

{

            string vnum = Session["num"].ToString();

            Session.Abandon();

            ViewState["num"] = vnum;

            if (this.TextBox1.Text == ViewState["num"].ToString())

            {

                Response.Write("<script>alert('驗證碼正确！')</script>");

                return;

            }

            else

            {

                Response.Write("<script>alert('驗證碼錯誤！')</script>");

                return;

            }

        }

了解了這三個關鍵點，我想，圖形驗證碼的編寫也可以自己勝任了。感謝網友的分享。

轉載于:https://www.cnblogs.com/snidget/archive/2011/02/10/1950654.html