• 作用：防止惡意注冊，惡意破解密碼，惡意灌水
• 分類：客戶端驗證和服務器端驗證。
• 關鍵問題：1，獲得一個隨機生成的字符串? 2，把字符串畫到網頁上。? 3.比較驗證

網上的代碼很多，自己也動手模仿了一個。

獲得一個隨機的字符串

?#region? 隨機取得數字字母
??????? 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.把字符串畫到網頁上

?? #region 把隨機數字和字母畫到圖片上
??????? 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('驗證碼正確！')</script>");
??????????????? return;
??????????? }
??????????? else
??????????? {
??????????????? Response.Write("<script>alert('驗證碼錯誤！')</script>");
??????????????? return;
??????????? }
??????? }

理解了這三個關鍵點，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

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