Detailed explanation of asp.net using ashx to implement verification code function

This article mainly introduces the method of asp.net using ashx to generate graphical verification codes. It analyzes the steps, implementation methods and related precautions of asp.net to generate graphical verification codes in the form of examples. Friends in need can refer to the following

The example in this article describes how asp.net uses ashx to generate graphic verification codes. I would like to share it with you for your reference. The details are as follows:

I don’t need to explain the benefits of verification code, you all know it. I saw on the Internet that someone wrote the verification code directly in the aspx page, which means that requesting the verification code in this way is equivalent to requesting a page. This is very unscientific. As shown below

<form id="form1" runat="server">
  <p>
    <asp:Image ID="Image1" runat="server" ImageUrl="Default.aspx" />
    <br />
    <asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
    <asp:Button ID="Button1" runat="server" onclick="Button1_Click" Text="Button" />
  </p>
</form>

Looking at this code, I feel that the person who wrote the code deserves a beating. It is really depressing to write the code like this. Verify it and don't write some script to switch.

Let me introduce a way to achieve this function

1. Write an ashx to generate a graphical verification code

using System;
using System.Collections;
using System.Data;
using System.Linq;
using System.Web;
using System.Web.Services;
using System.Web.Services.Protocols;
using System.Xml.Linq;
using System.Web.SessionState;
using System.Drawing;
namespace usechecknum.ashx
{
  /// <summary>
  /// $codebehindclassname$ 的摘要说明
  /// </summary>
  [WebService(Namespace = "http://tempuri.org/")]
  [WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)]
  public class doCreateNum : IHttpHandler,IRequiresSessionState
  {
    public void ProcessRequest(HttpContext context)
    {
      context.Response.ContentType = "text/html";
      string checkCode = GetValidation(5); // 产生5位随机验证码字符
      context.Session["Code"] = checkCode; //将字符串保存到Session中，以便需要时进行验证
      System.Drawing.Bitmap image = new System.Drawing.Bitmap(70, 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
        int i;
        for (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.Silver), x1, y1, x2, y2);
        }
        Font font = new System.Drawing.Font("Arial", 12, (System.Drawing.FontStyle.Bold));
        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
        g.DrawRectangle(new Pen(Color.Silver), 0, 0, image.Width - 1, image.Height - 1);
        System.IO.MemoryStream ms = new System.IO.MemoryStream();
        image.Save(ms, System.Drawing.Imaging.ImageFormat.Gif);
        context.Response.ClearContent();
        context.Response.ContentType = "image/Gif";
        context.Response.BinaryWrite(ms.ToArray());
      }
      finally
      {
        g.Dispose();
        image.Dispose();
      }
    }
    public string GetValidation(int num)
    {
      string str = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ"; //"或者写汉字也行"
      string validatecode = "";
      Random rd = new Random();
      for (int i = 0; i < num; i++)
      {
        validatecode += str.Substring(rd.Next(0, str.Length), 1);
      }
      return validatecode;
    }
    public bool IsReusable
    {
      get
      {
        return false;
      }
    }
  }
}

2. Display the verification code on the page. Because we generate graphics, we can write it directly in the tag. We only need to write a simple script to switch the verification code with a click of the mouse

<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="index.aspx.cs" Inherits="usechecknum._Default" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" >
<head runat="server">
  <title>验证码的使用</title>
</head>
<script language="javascript" type="text/javascript">
  function changeCode() {
    var imgNode = document.getElementById("vimg");
    imgNode.src = "ashx/doCreateNum.ashx?t=" + (new Date()).valueOf(); // 这里加个时间的参数是为了防止浏览器缓存的问题
  }
  </script>
<body>
  <form id="form1" runat="server">
   请输入验证码:<input type="text" name="checknum"/><img src="ashx/doCreateNum.ashx" id="vimg" onclick="changeCode()" />
  </form>
</body>
</html>

After talking for a long time, it’s time to see what the generated verification code looks like

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