asp.net 简易生成注册码（数字+大小写字母）

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生成随机码类：SigowayRandom.cs 
代码如下:
using System;
namespace RongYi.Model.Common
{
/// <summary>
/// SigowayRandom 的摘要说明
/// </summary>
public class SigowayRandom
{
#region 获取校验码

/// <summary>
/// 获取校验码
/// </summary>
/// <returns>校验码字符数组</returns>
public static string[] GetCheckCode()
{
string[] strCheckCode = new string[4];

// 已系统时间毫秒为随机种子
int nSeed = Convert.ToInt16(DateTime.Now.Millisecond);
Random random = new Random(nSeed);

// 产生0-9随机数
strCheckCode[0] = Convert.ToString(random.Next(1, 10));
// 产生a-z、A-Z随机字母
strCheckCode[1] = SigowayRandom.GetLetter(random);
strCheckCode[2] = Convert.ToString(random.Next(1, 10));
strCheckCode[3] = SigowayRandom.GetLetter(random);

// 返回校验码
return strCheckCode;
}

#endregion

#region 获取字母，区分大小写

/// <summary>
/// 获取字母，区分大小写
/// </summary>
/// <returns>大小写字母</returns>
private static string GetLetter(Random random)
{
// 随机数
int nChar = random.Next(65, 122);

// 非字母ASCII段
if (nChar >= 91 && nChar <= 96)
{
nChar -= 6;
}

return Convert.ToString((char)nChar);
}

#endregion
}
}


绘制校验码类：SigowayDraw.cs
代码如下:
using System.Drawing;
using System.Drawing.Imaging;
using System.Web;

namespace RongYi.Model.Common
{
/// <summary>
/// SigowayDraw 的摘要说明
/// </summary>
public class SigowayDraw
{
#region 构造方法

/// <summary>
/// 构造方法
/// </summary>
public SigowayDraw() { }

#endregion

#region 画校验码

/// <summary>
/// 画校验码
/// </summary>
/// <returns>校验码</returns>
public string DrawString()
{
// 设置字体
Font drawFont = new Font("Arial", 10);
// 创建位图元素
Bitmap objBitmap = new Bitmap(50, 20);
// 创建画图对象
Graphics objGraphics = Graphics.FromImage(objBitmap);
// 设置画布背景色
objGraphics.Clear(Color.White);
// 获取随机字符串
string[] strDrawString = SigowayRandom.GetCheckCode();

// 画字符串
objGraphics.DrawString(strDrawString[0], drawFont, new SolidBrush(Color.Purple), 1, 2);
objGraphics.DrawString(strDrawString[1], drawFont, new SolidBrush(Color.Green), 12, 2);
objGraphics.DrawString(strDrawString[2], drawFont, new SolidBrush(Color.Red), 24, 2);
objGraphics.DrawString(strDrawString[3], drawFont, new SolidBrush(Color.SteelBlue), 35, 2);

// 画干扰线
objGraphics.DrawLine(Pens.Silver, 5, 10, 40, 3);
objGraphics.DrawLine(Pens.Gray, 10, 5, 45, 15);