用C#实现验证码

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using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace validateCode
{
public partial class Login : Form
{
//随机码的长度
private const int CODELENGTH = 6;
//随机码
private String randomCode = "";
//随机码对应的图片

public Login()
{
InitializeComponent();
updatePic();
}
//更新验证码
private void updatePic()
{
randomCode = CreateRandomCode(CODELENGTH);
CreateImage(randomCode);
}
private string CreateRandomCode(int length)
{
int rand;
char code;
string randomCode = String.Empty;

//生成一定长度的验证码
System.Random random = new Random();
for (int i = 0; i < length; i++)
{
rand = random.Next();

if (rand % 3 == 0)
{
code = (char)('A' + (char)(rand % 26));
}
else
{
code = (char)('0' + (char)(rand % 10));
}

randomCode += code.ToString();
}
return randomCode;
}

/// 创建随机码图片
private void CreateImage(string randomCode)
{
try
{
int randAngle = 45; //随机转动角度
int mapwidth = (int)(randomCode.Length * 21);
Bitmap map = new Bitmap(mapwidth, 28);//创建图片背景

Graphics graph = Graphics.FromImage(map);
graph.Clear(Color.AliceBlue);//清除画面，填充背景
graph.DrawRectangle(new Pen(Color.Black, 0), 0, 0, map.Width - 1, map.Height - 1);//画一个边框
graph.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.AntiAlias;//模式

Random rand = new Random();

//背景噪点生成
Pen blackPen = new Pen(Color.LightGray, 0);
for (int i = 0; i < 50; i++)
{
int x = rand.Next(0, map.Width);
int y = rand.Next(0, map.Height);
graph.DrawRectangle(blackPen, x, y, 1, 1);
}

//验证码旋转，防止机器识别
char[] chars = randomCode.ToCharArray();//拆散字符串成单字符数组

//文字距中
StringFormat format = new StringFormat(StringFormatFlags.NoClip);
format.Alignment = StringAlignment.Center;
format.LineAlignment = StringAlignment.Center;

//定义颜色
Color[] c = { Color.Black, Color.Red, Color.DarkBlue, Color.Green, Color.Orange, Color.Brown, Color.DarkCyan, Color.Purple };
//定义字体
string[] font = { "Verdana", "Microsoft Sans Serif", "Comic Sans MS", "Arial", "宋体" };

for (int i = 0; i < chars.Length; i++)
{
int cindex = rand.Next(7);
int findex = rand.Next(5);

Font f = new System.Drawing.Font(font[findex], 13, System.Drawing.FontStyle.Bold);//字体样式(参数2为字体大小)
Brush b = new System.Drawing.SolidBrush(c[cindex]);

Point dot = new Point(16, 16);

float angle = rand.Next(-randAngle, randAngle);//转动的度数

graph.TranslateTransform(dot.X, dot.Y);//移动光标到指定位置
graph.RotateTransform(angle);
graph.DrawString(chars[i].ToString(), f, b, 1, 1, format);

graph.RotateTransform(-angle);//转回去
graph.TranslateTransform(2, -dot.Y);//移动光标到指定位置
}
pbVerifyCode.Image = map;

}
catch (ArgumentException)
{
MessageBox.Show("创建图片错误。");
}
}

private void btLogin_Click(object sender, EventArgs e)
{
if (randomCode.Equals(tbVerifyCode.Text.Trim()))
{
if (tbUserName.Text.Trim().Equals("stdManager") && tbPassword.Text.Trim().Equals("stdManager"))
{
MessageBox.Show("欢迎使用在线书城管理系统。");
}
}
else
{
MessageBox.Show("验证码错误,请重新输入.","输入错误");
updatePic();
tbVerifyCode.Text = "";
tbVerifyCode.Focus();
}
}

private void pbVerifyCode_Click(object sender, EventArgs e)
{
updatePic();
}

private void btExit_Click(object sender, EventArgs e)
{
if (MessageBox.Show("确定退出吗?", "退出", MessageBoxButtons.OKCancel, MessageBoxIcon.Exclamation) == DialogResult.OK)
{