.net登陆验证码

1. 新建aspx页面ValidateCode

2.ValidateCode.cs页面

/*
* 验证码
* */
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;

public partial class ValidateCode : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        //在page_load事件中调用Generate()和CreateCheckCodeImage()函数
        string str = GenerateCheckCode();
        CreateCheckCodeImage(str);
    }

    private string GenerateCheckCode()
    {
        //利用random()随机产生四位大写的字符串（包含数字和字母）

        int number;
        char code;
        string checkCode = string.Empty;
        Random random = new Random();
        for (int i = 0; i < 4; i++)
        {
            number = random.Next();

            //下面也可以用其他的方法构思
            if (number % 2 == 0)
                code = (char)('0' + (char)(number % 10));
            else
                code = (char)('A' + (char)(number % 26));
            checkCode += code.ToString();
        }

        //用cookies保存刚刚产生的随机字符串
         Session["CheckCode"] = checkCode;
        return checkCode;
    }

    private void CreateCheckCodeImage(string checkCode)
    {
        //该函数主要是画背景色的       

        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();
            //清空背景色
            g.Clear(Color.White);
            //画背景的噪音线
            for (int i = 0; i < 2; 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.Black), 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(60, 60, 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);
            Response.ClearContent();
            Response.ContentType = "image/Gif";
            Response.BinaryWrite(ms.ToArray());
        }
        finally
        {
            g.Dispose();
            image.Dispose();
        }
    }
}

3.登陆界面的使用:

.aspx页面

    <asp:Panel ID="Panel1" runat="server" Height="36px" Width="300" Visible="False">
                                <table cellpadding="0" cellspacing="0" style="width: 300px;">
                                    <tr>
                                        <td class="login_table_left">
                                            <asp:Label ID="Label3" runat="server" Text="验证码："></asp:Label>
                                        </td>
                                        <td class="login_table_center">
                                            <asp:TextBox ID="TextBox1" runat="server" Width="90px"></asp:TextBox>
                                        </td>
                                        <td class="login_table_last">
                                            <asp:Image ID="Image1" runat="server" ImageUrl="~/ValidateCode.aspx" />

<img src="ValidateCode.aspx" onclick="this.src='ValidateCode.aspx?'+new Date().getTime()";/>点击刷新验证码                                        </td>
                                    </tr>
                                </table>
     </asp:Panel>

.cs页面

   //判断验证码框是否显示如果显示就进行验证否则就登陆成功
string checkCode = this.TextBox1.Text.Trim();       

if (this.Panel1.Visible)
            {
                //判断验证码是否为空
                if (checkCode == "" || checkCode == null)
                {
                    this.Page.ClientScript.RegisterStartupScript(this.GetType(), Guid.NewGuid().ToString(), "<script>alert('请输入验证码！');</script>");
                    return;
                }
                else
                {
                    //判断验证码输入是否正确
                    if (String.Compare(Session["CheckCode"].ToString(), checkCode, true) != 0)
                    {
                        this.Page.ClientScript.RegisterStartupScript(this.GetType(), Guid.NewGuid().ToString(), "<script>alert('验证码错误！');</script>");
                        return;
                    }
                }
            }