asp.net无刷新实现：验证码

 

用一个页面生成图片，另一个页面调用，验证码存入cookie，调用时取cookie对比验证.这个用户就可以按自己的喜好更改效果和验证码的长度了 （： 效果如图：

代码如下：
CheckCode.aspx
using System;
using System.Data;
using System.Configuration;
using System.Collections;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.Drawing;
using System.Drawing.Drawing2D;
using System.Drawing.Imaging;
public partial class Tools_CheckCode : System.Web.UI.Page
{
     protected void Page_Load(object sender, EventArgs e)
     {
         this.CreateCheckCodeImage(GenerateCheckCode());
     }
     private string GenerateCheckCode()
     {
         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' + (char)(number % 10));
             else
                 code = (char)('A' + (char)(number % 26));
             checkCode += code.ToString();
         }
         Response.Cookies.Add(new HttpCookie("CheckCode", checkCode));
         return checkCode;
     }
     private void CreateCheckCodeImage(string checkCode)
     {
         if (checkCode == null || checkCode.Trim() == String.Empty)
             return;
         System.Drawing.Bitmap image = new System.Drawing.Bitmap((int)Math.Ceiling((checkCode.Length * 12.5)), 22);
         Graphics g = Graphics.FromImage(image);
         try
         {
             //生成随机生成器
             Random random = new Random();
             //清空图片背景色
             g.Clear(Color.White);
             //画图片的背景噪音线
             for (int i = 0; i < 25; i++)
             {
                 int x1 = random.Next(image.Width);
                 int x2 = random.Next(image.Width);
                 int y1 = random.Next(image.Height);
                 int y2 = random.Next(image.Height);
                 g.DrawLine(new Pen(Color.GreenYellow), x1, y1, x2, y2);
             }
             Font font = new System.Drawing.Font("Verdana", 12, (System.Drawing.FontStyle.Bold | System.Drawing.FontStyle.Italic));
             System.Drawing.Drawing2D.LinearGradientBrush brush = new System.Drawing.Drawing2D.LinearGradientBrush(new Rectangle(0, 0, image.Width, image.Height), Color.Blue, Color.DarkRed, 1.2f, true);
             g.DrawString(checkCode, font, brush, 2, 2);
             //画图片的前景噪音点
             for (int i = 0; i < 80; i++)
             {
                 int x = random.Next(image.Width);
                 int y = random.Next(image.Height);
                 image.SetPixel(x, y, Color.FromArgb(random.Next()));
             }
             //画图片的边框线
             g.DrawRectangle(new Pen(Color.Red), 0, 0, image.Width - 1, image.Height - 1);
             System.IO.MemoryStream ms = new System.IO.MemoryStream();
             image.Save(ms, System.Drawing.Imaging.ImageFormat.Gif);
             Response.ClearContent();
             Response.ContentType = "image/Gif";
             Response.BinaryWrite(ms.ToArray());
         }
         finally
         {
             g.Dispose();
             image.Dispose();
         }
     }

}
然后在需要使用的页面引用：
UseCheckCode.aspx
<img src="Tools/CheckCode.aspx" alt="验证码" style="width: 60px; height: 24px" />
3.用web handler生成图片。这个其实和前面的意思大致差不多，调用方法也基本和2一样,不同的是，他的验证码是存入Session的。供学习参考。
效果图如下：

ValidateImageHandler.ashx
<%@ WebHandler Language="C#" Class="ValidateImageHandler" %>
using System;
using System.Web;
using System.Web.SessionState;
using System.Drawing;
using System.Drawing.Imaging;
using System.Text;
/**//// <summary>
/// ValidateImageHandler 生成网站验证码功能
/// </summary>
public class ValidateImageHandler : IHttpHandler, IRequiresSessionState
{
     int intLength = 5;               //长度
     string strIdentify = "Identify"; //随机字串存储键值，以便存储到Session中
     public ValidateImageHandler()
     {        
     }
     /**//// <summary>
     /// 生成验证图片核心代码
     /// </summary>
     /// <param name="hc"></param>
     public void ProcessRequest(HttpContext hc)
     {
         //设置输出流图片格式
         hc.Response.ContentType = "image/gif";
        
         Bitmap b = new Bitmap(200, 60);
         Graphics g = Graphics.FromImage(b);
         g.FillRectangle(new SolidBrush(Color.YellowGreen), 0, 0, 200, 60);
         Font font = new Font(FontFamily.GenericSerif, 48, FontStyle.Bold, GraphicsUnit.Pixel);
         Random r = new Random();
         //合法随机显示字符列表
         string strLetters = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890";
         StringBuilder s = new StringBuilder();
        
         //将随机生成的字符串绘制到图片上
         for (int i = 0; i < intLength; i++)
         {
             s.Append(strLetters.Substring(r.Next(0, strLetters.Length - 1), 1));
             g.DrawString(s[s.Length - 1].ToString(), font, new SolidBrush(Color.Blue), i * 38, r.Next(0, 15));
         }
         //生成干扰线条
         Pen pen = new Pen(new SolidBrush(Color.Blue), 2);
         for (int i = 0; i < 10; i++)
         {
             g.DrawLine(pen, new Point(r.Next(0, 199), r.Next(0, 59)), new Point(r.Next(0, 199), r.Next(0, 59)));
         }
         b.Save(hc.Response.OutputStream, ImageFormat.Gif);
         hc.Session[strIdentify] = s.ToString(); //先保存在Session中，验证与用户输入是否一致
         hc.Response.End();
  
     }
    
     /**//// <summary>
     /// 表示此类实例是否可以被多个请求共用(重用可以提高性能)
     /// </summary>
     public bool IsReusablea
     {
         get
         {
             return true;
         }
     }