详解ASP.NET验证码的生成方法

*完整程序

先在VS2005里面的项目里面添加一个 checkCode.aspx 文件，在checkCode.aspx.cs 代码文件中添加如下完整代码

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.IO;
using System.Drawing.Drawing2D;

public partial class checkCode : System.Web.UI.Page
{
  protected void Page_Load(object sender, EventArgs e)
  {
    CreateCheckCodeImage(GenerateCheckCode());//调用下面两个方法;
  }

  /// <summary>
  /// 生成验证码的随机数
  /// </summary>
  /// <returns>返回五位随机数</returns>
  private string GenerateCheckCode()
  {
    int number;
    char code;
    string checkCode = String.Empty;

    Random random = new Random();

    for (int i = 0; i < 5; i++)//可以任意设定生成验证码的位数
    {
      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));//写入COOKIS
    Session["CheckCode"] = checkCode; //写入Session，可以任意选一下
    return checkCode;
  }


  /// <summary>
  /// 生成验证码图片
  /// </summary>
  /// <param name="checkCode"></param>
  private void CreateCheckCodeImage(string checkCode)
  {
    if (checkCode == null || checkCode.Trim() == String.Empty)
      return;

    Bitmap image = new 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.Silver), x1, y1, x2, y2);
      }

      Font font = new System.Drawing.Font("Arial", 12, (System.Drawing.FontStyle.Bold | System.Drawing.FontStyle.Italic));
      LinearGradientBrush brush = new 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);

      MemoryStream ms = new MemoryStream();
      image.Save(ms, System.Drawing.Imaging.ImageFormat.Gif);
      Response.ClearContent();
      Response.ContentType = "image/Gif";
      Response.BinaryWrite(ms.ToArray());
    }
    finally
    {//释放对象资源
      g.Dispose();
      image.Dispose();
    }
  }

}

								 
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