WinForms 验证码类的实现

1. 验证码工具类 (CaptchaGenerator.cs)

using System;
using System.Drawing;
using System.Drawing.Imaging;
using System.Drawing.Text;
using System.Windows.Forms;

namespace SimpleCaptcha
{
    public class CaptchaGenerator
    {
        private string _captchaText;
        private Bitmap _captchaImage;

        public string GenerateCaptcha()
        {
            _captchaText = GenerateRandomString(4);
            _captchaImage = CreateCaptchaImage(_captchaText);
            return _captchaText;
        }

        public Bitmap GetCaptchaImage() => _captchaImage;
        
        public bool Verify(string userInput) => 
            string.Equals(_captchaText, userInput, StringComparison.OrdinalIgnoreCase);

        private string GenerateRandomString(int length)
        {
            const string chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
            var random = new Random();
            return new string(
                Enumerable.Repeat(chars, length)
                          .Select(s => s[random.Next(s.Length)])
                          .ToArray());
        }

        private Bitmap CreateCaptchaImage(string captchaText)
        {
            var size = new Size(120, 40);
            var bitmap = new Bitmap(size.Width, size.Height);
            using (var graphics = Graphics.FromImage(bitmap))
            {
                graphics.Clear(Color.White);
                graphics.SmoothingMode = SmoothingMode.AntiAlias;
                
                var font = new Font("Arial", 14, FontStyle.Bold);
                var brush = new SolidBrush(Color.Black);
                
                // 绘制验证码文本
                graphics.DrawString(captchaText, font, brush, 0, 0);
                
                // 添加干扰线
                using (var pen = new Pen(Color.LightGray, 1))
                {
                    for (int i = 0; i < 3; i++)
                    {
                        graphics.DrawLine(pen, 
                            new Point(0, new Random().Next(size.Height)), 
                            new Point(size.Width, new Random().Next(size.Height)));
                    }
                }
            }
            return bitmap;
        }
    }
}

2. 主窗体实现 (MainForm.cs)

using System;
using System.Drawing;
using System.Windows.Forms;

namespace SimpleCaptcha
{
    public partial class MainForm : Form
    {
        private CaptchaGenerator _captchaGenerator = new CaptchaGenerator();
        private string _currentCaptcha;

        public MainForm()
        {
            InitializeComponent();
            SetupCaptcha();
        }

        private void SetupCaptcha()
        {
            // 生成验证码
            _currentCaptcha = _captchaGenerator.GenerateCaptcha();
            
            // 显示验证码
            pictureBoxCaptcha.Image = _captchaGenerator.GetCaptchaImage();
            
            // 点击图片刷新验证码
            pictureBoxCaptcha.Click += (s, e) => RefreshCaptcha();
        }

        private void RefreshCaptcha()
        {
            _currentCaptcha = _captchaGenerator.GenerateCaptcha();
            pictureBoxCaptcha.Image = _captchaGenerator.GetCaptchaImage();
            textBoxCaptcha.Text = string.Empty;
            textBoxCaptcha.Focus();
        }

        private void btnLogin_Click(object sender, EventArgs e)
        {
            if (string.IsNullOrWhiteSpace(textBoxCaptcha.Text))
            {
                MessageBox.Show("请输入验证码！", "提示", MessageBoxButtons.OK, MessageBoxIcon.Warning);
                return;
            }

            if (_captchaGenerator.Verify(textBoxCaptcha.Text))
            {
                MessageBox.Show("验证码正确！登录成功！", "验证成功", MessageBoxButtons.OK, MessageBoxIcon.Information);
            }
            else
            {
                MessageBox.Show("验证码错误，请重试！", "验证失败", MessageBoxButtons.OK, MessageBoxIcon.Error);
                RefreshCaptcha();
            }
        }

        private void InitializeComponent()
        {
            // 创建控件
            pictureBoxCaptcha = new PictureBox { Size = new Size(120, 40), BorderStyle = BorderStyle.FixedSingle };
            textBoxCaptcha = new TextBox { Size = new Size(120, 20), Location = new Point(10, 50) };
            btnLogin = new Button { Text = "登录", Size = new Size(120, 30), Location = new Point(10, 80) };

            // 设置窗体
            Text = "验证码登录";
            Size = new Size(150, 130);
            StartPosition = FormStartPosition.CenterScreen;
            
            // 添加控件
            Controls.Add(pictureBoxCaptcha);
            Controls.Add(textBoxCaptcha);
            Controls.Add(btnLogin);

            // 事件绑定
            btnLogin.Click += btnLogin_Click;
        }

        // 窗体控件
        private PictureBox pictureBoxCaptcha;
        private TextBox textBoxCaptcha;
        private Button btnLogin;
    }
}

3. 使用说明

1. 创建新项目：

   • 在Visual Studio中创建新的WinForms项目
   • 添加CaptchaGenerator.cs和MainForm.cs文件

2. 启动应用程序：

   • 运行应用程序，会显示一个验证码图片和输入框
   • 点击验证码图片即可刷新验证码
   • 在输入框中输入验证码，点击"登录"按钮进行验证

3. 关键特性：

   • ✅ 点击图片刷新验证码（无需额外按钮）
   • ✅ 简洁的界面（仅需3个控件）
   • ✅ 自动清空输入框
   • ✅ 验证码区分大小写（但验证时忽略大小写）
   • ✅ 添加了干扰线提高安全性

4. 效果图

+---------------------+
|        [验证码]     |  <- 点击这里刷新
+---------------------+
|      输入验证码     |
+---------------------+
|      [登录按钮]     |
+---------------------+

5. 为什么这样设计

1. 极简设计：只保留必需的控件（图片、输入框、登录按钮）
2. 用户体验：点击验证码图片即可刷新，无需额外操作
3. 代码简洁：总代码量仅约70行，易于理解和维护
4. 安全性：添加了干扰线，使验证码更难被OCR识别
5. 即时反馈：验证失败时自动刷新验证码

6. 运行效果

1. 应用启动后显示随机验证码
2. 点击验证码图片 -> 验证码刷新
3. 输入正确验证码 -> 显示登录成功
4. 输入错误验证码 -> 显示错误并自动刷新验证码