验证码总是错误

Question

这是生成验证码的代码。using System;
using System.Collections;
using System.Configuration;
using System.Data;
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;
public partial class checkcode : System.Web.UI.Page
{    protected void Page_Load(object sender, EventArgs e)
    {
        CreateCheckCodeImage(GenerateCheckCode());
        Session["snow"] = GenerateCheckCode();
    }
    private string GenerateCheckCode() //生成验证码
    {
        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();
        }
        Response.Cookies.Add(new HttpCookie("CheckCode", checkCode));        return checkCode;
    }    private void CreateCheckCodeImage(string checkCode)  //生成验证图片
    {
        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
        {            Random random = new Random();   //生成随机生成器            g.Clear(Color.White);   //清空图片背景色            for (int i = 0; i < 2; i++)   //画图片的背景噪音线
            {
                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.Black), 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);            for (int i = 0; i < 100; i++)  //画图片的前景噪音点
            {
                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);
            Response.ClearContent();
            Response.ContentType = "image/Gif";
            Response.BinaryWrite(ms.ToArray());
        }
        finally
        {
            g.Dispose();
            image.Dispose();
        }
    }
}下面为调用验证功能：
 if (TextBox3.Text.Trim() != Session["snow"].ToString())
            {
                Response.Write("<script>alert('验证码错误！');</script>");
            }
结果无论向TextBox3输入什么总是“验证码错误！”

Answer 1

单步跟踪看看checkCode
if (Session["snow"].ToString().Equals(TextBox3.Text.Trim()))
{}
 

Answer 2

    protected void Page_Load(object sender, EventArgs e)
    {
        CreateCheckCodeImage(GenerateCheckCode());
        Session["snow"] = GenerateCheckCode();
    }
应该改为：
    protected void Page_Load(object sender, EventArgs e)
    {
        string Code=GenerateCheckCode();
        CreateCheckCodeImage(Code);
        Session["snow"] = Code;
    }你两次执行函数，返回值自然不同。

Answer 3

if(!IsPostBack)
{
CreateCheckCodeImage(GenerateCheckCode());
Session["snow"] = GenerateCheckCode();
}
验证码是否与登录在一个页面