C# WinForm 登录界面的图片验证码(区分大小写+不区分大小写)

一、功能界面

图1 验证码(区分大小写)

图2 验证码(不区分大小写)

二、创建一个产生验证码的类class1

（1）生成随机验证码字符串，用的是random随机函数
（2）创建验证码图片，将该字符串画在picturebox控件中

class1.cs：

using system;
using system.collections.generic;
using system.linq;
using system.text;
using system.threading.tasks;
using system.drawing;//图片
using system.windows.forms;

namespace validcodetest
{
  public class class1
  {
    #region 验证码功能      
    /// <summary>
    /// 生成随机验证码字符串
    /// </summary>
    public static string createrandomcode(int codelength) 
    {
      int rand;
      char code;
      string randomcode = string.empty;//随机验证码
     	
     	//生成一定长度的随机验证码    
      //random random = new random();//生成随机数对象
      for (int i = 0; i < codelength; i++)
      {
        //利用guid生成6位随机数   
        byte[] buffer = guid.newguid().tobytearray();//生成字节数组
        int seed = bitconverter.toint32(buffer, 0);//利用bitconvert方法把字节数组转换为整数
        random random = new random(seed);//以生成的整数作为随机种子
        rand = random.next();

        //rand = random.next();   
        if (rand % 3 == 1)
        {
          code = (char)('a' + (char)(rand % 26));
        }
        else if (rand % 3 == 2)
        {
          code = (char)('a' + (char)(rand % 26));          
        }
        else
        {
          code = (char)('0' + (char)(rand % 10));
        }
        randomcode += code.tostring();
      }
      return randomcode;
    }

    /// <summary>
    /// 创建验证码图片
    /// </summary>
    public static void createimage(string strvalidcode, picturebox pbox)
    {
      try
      {
        int randangle = 45;//随机转动角度
        int mapwidth = (int)(strvalidcode.length * 21);
        bitmap map = new bitmap(mapwidth, 28);//验证码图片—长和宽

				//创建绘图对象graphics
        graphics graph = graphics.fromimage(map);
        graph.clear(color.aliceblue);//清除绘画面,填充背景色
        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 = strvalidcode.tochararray();//拆散字符串成单字符数组
        //文字居中
        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
        }
        pbox.image = map;
      }
      catch (argumentexception)
      {
        messagebox.show("验证码图片创建错误");
      }
    }
    #endregion
  }
}

三、调用

（1）更新验证码
（2）验证（区分大小写）
（3）验证（不区分大小写）

form1.cs：

using system;
using system.collections.generic;
using system.componentmodel;
using system.data;
using system.drawing;
using system.linq;
using system.text;
using system.threading.tasks;
using system.windows.forms;
using validcodetest;

namespace validcode
{
  public partial class form1 : form
  {
    public form1()
    {
      initializecomponent();
    }


    #region 验证码
    private const int validcodelength = 4;//验证码长度    
    private string strvalidcode = "";//验证码            

    //调用自定义函数,更新验证码
    private void updatevalidcode()
    {
      strvalidcode = class1.createrandomcode(validcodelength);//生成随机验证码
      if (strvalidcode == "") return;
      class1.createimage(strvalidcode, pbox1);//创建验证码图片
    }
    #endregion


    private void pbox1_click(object sender, eventargs e)
    {
      updatevalidcode();//点击更新验证码
    }


    private void form1_load(object sender, eventargs e)
    {
      updatevalidcode();//加载更新验证码
    }


    /// <summary>
    /// 验证（区分大小写）
    /// </summary>    
    private void btn1_click(object sender, eventargs e)
    {
      string validcode = txtvalidcode.text.trim();

      char[] ch1 = validcode.tochararray();
      char[] ch2 = strvalidcode.tochararray();
      int count1 = 0;//字母个数
      int count2 = 0;//数字个数

      if (string.isnullorempty(validcode) != true)//验证码不为空
      {
        for (int i = 0; i < strvalidcode.length; i++)
        {
          if ((ch1[i] >= 'a' && ch1[i] <= 'z') || (ch1[i] >= 'a' && ch1[i] <= 'z'))//字母
          {
            if (ch1[i] == ch2[i])
            {
              count1++;
            }
          }
          else//数字
          {
            if (ch1[i] == ch2[i])
            {
              count2++;
            }
          }

        }

        int countsum = count1 + count2;
        if (countsum == strvalidcode.length)
        {
          messagebox.show("验证通过", "提示", messageboxbuttons.ok, messageboxicon.information);
          updatevalidcode();
          txtvalidcode.text = "";
          txtvalidcode.focus();
        }
        else
        {
          messagebox.show("验证失败", "警告", messageboxbuttons.ok, messageboxicon.exclamation);
          updatevalidcode();//更新验证码
          txtvalidcode.text = "";
          txtvalidcode.focus();
        }
      }
      else//验证码为空
      {
        messagebox.show("请输入验证码", "提示", messageboxbuttons.ok, messageboxicon.information);
        updatevalidcode();//更新验证码
        txtvalidcode.text = "";
        txtvalidcode.focus();
      }
    }


    /// <summary>
    /// 验证（不区分大小写）
    /// </summary> 
    private void btn2_click(object sender, eventargs e)
    {
      string validcode = txtvalidcode.text.trim();

      if (string.isnullorempty(validcode) != true)//验证码不为空
      {
        if (validcode.tolower() == strvalidcode.tolower())
        {
          messagebox.show("验证通过", "提示", messageboxbuttons.ok, messageboxicon.information);
          updatevalidcode();
          txtvalidcode.text = "";
          txtvalidcode.focus();
        }
        else
        {
          messagebox.show("验证失败", "警告", messageboxbuttons.ok, messageboxicon.exclamation);
          updatevalidcode();//更新验证码
          txtvalidcode.text = "";
          txtvalidcode.focus();
        }
      }
      else//验证码为空
      {
        messagebox.show("请输入验证码", "提示", messageboxbuttons.ok, messageboxicon.information);
        updatevalidcode();//更新验证码
        txtvalidcode.text = "";
        txtvalidcode.focus();
      }
    }
  }
}

.exe测试文件下载: validcode_jb51.zip

参考文章：
https://www.jianshu.com/p/d89f22cf51bf

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