在ashx文件中制作验证码（使用session要继承IRequiresSessionState）

【网络转载】注意：
必须继承System.Web.SessionState.IRequiresSessionState接口，才能实现Session读写！

System.Web.SessionState的一些接口

IReadOnlySessionState 指定目标 HTTP 处理程序只需要具有对会话状态值的读访问权限。这是一个标记接口，没有任何方法。
IRequiresSessionState 指定目标 HTTP 处理程序需要对会话状态值具有读写访问权。这是一个标记接口，没有任何方法。

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ashx文件

<%@ WebHandler Language="C#" Class="CheckCode" %>

using System;
using System.Web;
using System.Drawing;
using System.Web.SessionState;

public class CheckCode : IHttpHandler,IRequiresSessionState
{

public void ProcessRequest(HttpContext context)
{
context.Response.ContentType = "text/plain";
string code = GenerateCheckCode();
context.Session["code"] = code;
this.CreateCheckCodeImage(code,context);
}
private string GenerateCheckCode()
{
int number;
char code;
string checkCode = String.Empty;

System.Random random = new Random();

for (int i = 0; i < 4; i++)
{
number = random.Next();

if (number % 2 == 0)
code = (char)('0' + (char)(number % 10));
else
code = (char)('A' + (char)(number % 26));

checkCode += code.ToString();
}

return checkCode;
}

private void CreateCheckCodeImage(string checkCode, HttpContext context)
{
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 < 5; 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.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 < 100; 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.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 bool IsReusable {
get {
return false;
}
}

}

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页面验证时
<img src="ashx文件地址">

判断验证码是否正确
Session["code"].ToString()==用户输入的文本框的值