ASP随机四位数字验证码

首先需要一个验证码类，放在App_Code

using System;

using System.Data;

using System.Configuration;

using System.Linq;

using System.Web;

using System.Web.Security;

using System.Web.UI;

using System.Web.UI.HtmlControls;

using System.Web.UI.WebControls;

using System.Web.UI.WebControls.WebParts;

using System.Xml.Linq;

using System.Drawing ;

/// <summary>

///CheckCodeImage 的摘要说明

/// </summary>

public class CheckCodeImage

{

    /// <summary>

    /// 生成随机验证码，四位数

    /// </summary>

    private HttpResponse Response;
public CheckCodeImage(HttpResponse response)
{

        this.Response = response;
}

    public string GetCheckCode()

    {

        int num;

        char code;

        string checkCode = string.Empty;

        System.Random random = new Random();

        for (int i = 0; i < 4; i++)

        {

            num = random.Next();

            code = (char)('0' + (char)(num % 10));

            checkCode += code.ToString();

        }

        return checkCode;

    }

    public void CreatCheckCodeImage(string checkCode)

    {

        //不允许验证码为空

        if(checkCode==null ||checkCode.Trim ()==string .Empty )

        {return ;}

        System .Drawing .Bitmap image=new Bitmap ((int)Math .Ceiling ((checkCode .Length *12.5)),22);//验证码图片的高度和宽度

        Graphics g=Graphics .FromImage (image );

        Random random=new Random ();

        //清空图片背景色

        g.Clear (Color.White );

        for (int i=0;i<44;i++)

        {

            int x1=random .Next (image .Width -i);

            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 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);

        //画前景噪音点

        for (int i = 0; i < 36; 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);

        Response.ClearContent();

        Response.ContentType = "image/Gif";

        Response.BinaryWrite(ms.ToArray());

        

    }
}

新建一个页面(default.aspx)，后台代码如下

protected void Page_Load(object sender, EventArgs e)

    {

        CheckCodeImage image = new CheckCodeImage(this.Response);

        string strCheckCode = image.GetCheckCode();

        Session.Add("checkcode", strCheckCode);

        image.CreatCheckCodeImage(strCheckCode);

    }

最后，在需要用验证码的界面，添加一个image控件，设置控件url为default.aspx.