ASP.net 驗證碼(C#)

/* Copyright all(c) 2005 ZhongFeng, http://blog.csdn.net/SW515 */
public class ValidateCode : System.Web.UI.Page
{
private void Page_Load(object sender, System.EventArgs e)
{
this.CreateCheckCodeImage(GenerateCheckCode());
}

#region Web 窗體設計器生成的代碼
override protected void OnInit(EventArgs e)
{
//
// CODEGEN: 該調用是 ASP.NET Web 窗體設計器所必需的。
//
InitializeComponent();
base.OnInit(e);
}

/// <summary>
/// 設計器支持所需的方法 - 不要使用代碼編輯器修改
/// 此方法的內容。
/// </summary>
private void InitializeComponent()
{
this.Load += new System.EventHandler(this.Page_Load);
}
#endregion

private string GenerateCheckCode()
{
int number;
char code;
string checkCode = String.Empty;

System.Random random = new Random();

for(int i=0; i<5; i++)
{
number = random.Next();

if(number % 2 == 0)
code = (char)('0' + (char)(number % 10));
else
code = (char)('A' + (char)(number % 26));

checkCode += code.ToString();
}

Response.Cookies.Add(new HttpCookie("CheckCode", checkCode));

return checkCode;
}

private void CreateCheckCodeImage(string checkCode)
{
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
{
//生成隨機生成器
Random random = new Random();

//清空圖片背景色
g.Clear(Color.White);

//畫圖片的背景噪音線
for(int i=0; i<25; 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.Silver), x1, y1, x2, y2);
}

Font font = new System.Drawing.Font("Arial", 12, (System.Drawing.FontStyle.Bold | System.Drawing.FontStyle.Italic));
System.Drawing.Drawing2D.LinearGradientBrush brush = new System.Drawing.Drawing2D.LinearGradientBrush(new Rectangle(0, 0, image.Width, image.Height), Color.Blue, Color.DarkRed, 1.2f, true);
g.DrawString(checkCode, font, brush, 2, 2);

//畫圖片的前景噪音點
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()));
}

//畫圖片的邊框線
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();
}
}
}

　　假如以上驗證碼生成器頁面名為：CheckCode.aspx，那麼在登錄頁面中使用“<IMG>” 這個 HTML 元素來顯示生成的驗證碼圖片：<IMG src="CheckCode.aspx">
　　在登錄頁面的登錄按鈕的處理事件中使用以下代碼判斷驗證碼：

private void btnLogin_Click(object sender, System.Web.UI.ImageClickEventArgs e)
{
if(Request.Cookies["CheckCode"] == null)
{
lblMessage.Text = "您的浏覽器設置已被禁用 Cookies，您必須設置浏覽器允許使用 Cookies 選項後才能使用本系統。";
lblMessage.Visible = true;
return;
}

if(String.Compare(Request.Cookies["CheckCode"].Value, txtCheckCode.Text, true) != 0)
{
lblMessage.Text = "驗證碼錯誤，請輸入正確的驗證碼。";
lblMessage.Visible = true;
return;
}

/***** 其他代碼 *****/

}