图片验证码

private void Page_Load(object sender, System.EventArgs e)
           {
               string checkCode = GetRandomCode(4);
               Session["ValidateCode"] = checkCode;
              SetPageNoCache();
              CreateImage(checkCode);
          }
  
          /// <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");
          }
  
          private string CreateRandomCode(int codeCount)
          {
              string allChar = "0,1,2,3,4,5,6,7,8,9,A,B,C,D,E,F,G,H,i,J,K,M,N,P,Q,R,S,T,U,W,X,Y,Z";
              string[] allCharArray = allChar.Split(',');
              string randomCode = "";
              int temp = -1;
  
              Random rand = new Random();
              for (int i = 0; i < codeCount; i++)
              {
                  if (temp != -1)
                  {
                      rand = new Random(i * temp * ((int)DateTime.Now.Ticks));
                  }
                  int t = rand.Next(35);
                  if (temp == t)
                  {
                      return CreateRandomCode(codeCount);//性能问题
                  }
                  temp = t;
                  randomCode += allCharArray[t];
              }
              return randomCode;
          }
          private string GetRandomCode(int CodeCount)
          {
              string allChar = "0,1,2,3,4,5,6,7,8,9,A,B,C,D,E,F,G,H,i,J,K,M,N,P,Q,R,S,T,U,W,X,Y,Z";
              string[] allCharArray = allChar.Split(',');
              string RandomCode = "";
              int temp = -1;
  
              Random rand = new Random();
              for (int i = 0; i < CodeCount; i++)
              {
                  if (temp != -1)
                  {
                      rand = new Random(temp * i * ((int)DateTime.Now.Ticks));
                  }
  
                  int t = rand.Next(33);
  
                  while (temp == t)
                  {
                      t = rand.Next(33);
                  }
  
                  temp = t;
                  RandomCode += allCharArray[t];
              }
  
             return RandomCode;
          }
          private void CreateImage(string checkCode)
          {
              int iwidth = (int)(checkCode.Length * 14);
              System.Drawing.Bitmap image = new System.Drawing.Bitmap(iwidth, 20);
              Graphics g = Graphics.FromImage(image);
              Font f = new System.Drawing.Font("Arial ", 10, System.Drawing.FontStyle.Bold);
              Brush b = new System.Drawing.SolidBrush(Color.FromArgb(255,255,255));
              Brush r = new System.Drawing.SolidBrush(Color.FromArgb(255,0,0));
  
              //g.FillRectangle(new System.Drawing.SolidBrush(Color.Blue),0,0,image.Width, image.Height);
              //g.Clear(Color.AliceBlue);//背景色
              g.Clear(System.Drawing.ColorTranslator.FromHtml("#79808B"));//背景色
  
              char[] ch = checkCode.ToCharArray();
              for (int i = 0; i < ch.Length; i++)
              {
                  if (ch[i] >= '0' && ch[i] <= '9')
                  {
                      //数字用红色显示
                      g.DrawString(ch[i].ToString(), f, r, 3 + (i * 12), 3);
                  }
                 else
                 {   //字母用黑色显示
                     g.DrawString(ch[i].ToString(), f, b, 3 + (i * 12), 3);
                 }
             }
 
 
             System.IO.MemoryStream ms = new System.IO.MemoryStream();
             image.Save(ms, System.Drawing.Imaging.ImageFormat.Jpeg);
             //history back 不重复 
             Response.Cache.SetNoStore();//这一句         
             Response.ClearContent();
             Response.ContentType = "image/Jpeg";
             Response.BinaryWrite(ms.ToArray());
             g.Dispose();
             image.Dispose();
        }