asp.net验证码生成和刷新及验证

验证码技术是为了防止暴力破解等而设定的。现在一般的网站注册等都提供验证码功能，特别是腾讯更是长长的一串。文中参考了http://www.cnblogs.com/netflu/archive/2007/01/10/242038.html的代码。有了就没有必要再写了。可以读一下。不过我测试时发现了两次PageLoad的问题。注释了两句即可。同时修改了namespaces。同时提供完整的验证说明：
1 新建VerifyCode.aspx
cs文件代码如下：


using System;


using System.Collections;


using System.ComponentModel;


using System.Data;


using System.Web;


using System.Web.SessionState;


using System.Web.UI;


using System.Web.UI.WebControls;


using System.Web.UI.HtmlControls;




using System.Drawing;


using System.Drawing.Imaging;


using System.Drawing.Text;






/**///// <summary>


/// 页面验证码程序


/// 使用：在页面中加入HTML代码 <img src="VerifyCode.aspx">


/// </summary>


public partial class VerifyCode : System.Web.UI.Page




...{








static string[] FontItems = new string[] ...{ "Arial",


"Helvetica",


"Geneva",


"sans-serif",


"Verdana"


};






static Brush[] BrushItems = new Brush[] ...{ Brushes.OliveDrab,


Brushes.ForestGreen,


Brushes.DarkCyan,


Brushes.LightSlateGray,


Brushes.RoyalBlue,


Brushes.SlateBlue,


Brushes.DarkViolet,


Brushes.MediumVioletRed,


Brushes.IndianRed,


Brushes.Firebrick,


Brushes.Chocolate,


Brushes.Peru,


Brushes.Goldenrod


};






static string[] BrushName = new string[] ...{ "OliveDrab",


"ForestGreen",


"DarkCyan",


"LightSlateGray",


"RoyalBlue",


"SlateBlue",


"DarkViolet",


"MediumVioletRed",


"IndianRed",


"Firebrick",


"Chocolate",


"Peru",


"Goldenrod"


};




private static Color BackColor = Color.White;


private static Pen BorderColor = Pens.DarkGray;


private static int Width = 52;


private static int Height = 21;




private Random _random;


private string _code;


private int _brushNameIndex;






override protected void OnInit(EventArgs e)




...{


//


// CODEGEN: This call is required by the ASP.NET Web Form Designer.


//


//InitializeComponent();


//base.OnInit(e);


}






/**//**//**//// <summary>


/// Required method for Designer support - do not modify


/// the contents of this method with the code editor.


/// </summary>


private void InitializeComponent()




...{


//this.Load += new System.EventHandler(this.Page_Load);


}










/**//// <summary>


///


/// </summary>


/// <param name="sender"></param>


/// <param name="e"></param>


public void Page_Load(object sender, System.EventArgs e)




...{


if (!IsPostBack)




...{


//


// TODO : initialize


//


this._random = new Random();


this._code = GetRandomCode();




//


// TODO : use Session["code"] save the VerifyCode


//


Session["code"] = this._code;




//


// TODO : output Image


//


this.SetPageNoCache();


this.OnPaint();


}


}












/**//**//**//// <summary>


/// 设置页面不被缓存


/// </summary>


private void SetPageNoCache()




...{


Response.Buffer = true;


Response.ExpiresAbsolute = System.DateTime.Now.AddSeconds(-1);


Response.Expires = 0;


Response.CacheControl = "no-cache";


Response.AppendHeader("Pragma","No-Cache");


}






/**//**//**//// <summary>


/// 取得一个 4 位的随机码


/// </summary>


/// <returns></returns>


private string GetRandomCode()




...{


return Guid.NewGuid().ToString().Substring(0, 4);


}






/**//**//**//// <summary>


/// 随机取一个字体


/// </summary>


/// <returns></returns>


private Font GetFont()




...{


int fontIndex = _random.Next(0, FontItems.Length);


FontStyle fontStyle = GetFontStyle(_random.Next(0, 2));


return new Font(FontItems[fontIndex], 12, fontStyle);


}






/**//**//**//// <summary>


/// 取一个字体的样式


/// </summary>


/// <param name="index"></param>


/// <returns></returns>


private FontStyle GetFontStyle(int index)




...{


switch (index)




...{


case 0:


return FontStyle.Bold;


case 1:


return FontStyle.Italic;


default:


return FontStyle.Regular;


}


}






/**//**//**//// <summary>


/// 随机取一个笔刷


/// </summary>


/// <returns></returns>


private Brush GetBrush()




...{


int brushIndex = _random.Next(0, BrushItems.Length);


_brushNameIndex = brushIndex;


return BrushItems[brushIndex];


}










/**//**//**//// <summary>


/// 绘画事件


/// </summary>


private void OnPaint()




...{


Bitmap objBitmap = null;


Graphics g = null;




try




...{


objBitmap = new Bitmap(Width, Height);


g = Graphics.FromImage(objBitmap);




Paint_Background(g);


Paint_Text(g);


Paint_TextStain(objBitmap);


Paint_Border(g);




objBitmap.Save(Response.OutputStream, ImageFormat.Gif);


Response.ContentType = "image/gif";


}




catch ...{}


finally




...{


if (null != objBitmap)


objBitmap.Dispose();


if (null != g)


g.Dispose();


}


}






/**//**//**//// <summary>


/// 绘画背景颜色


/// </summary>


/// <param name="g"></param>


private void Paint_Background(Graphics g)




...{


g.Clear(BackColor);


}






/**//**//**//// <summary>


/// 绘画边框


/// </summary>


/// <param name="g"></param>


private void Paint_Border(Graphics g)




...{


g.DrawRectangle(BorderColor, 0, 0, Width - 1, Height - 1);


}






/**//**//**//// <summary>


/// 绘画文字


/// </summary>


/// <param name="g"></param>


private void Paint_Text(Graphics g)




...{


g.DrawString(_code, GetFont(), GetBrush(), 3, 1);


}






/**//**//**//// <summary>


/// 绘画文字噪音点


/// </summary>


/// <param name="g"></param>


private void Paint_TextStain(Bitmap b)




...{


for (int n=0; n<30; n++)




...{


int x = _random.Next(Width);


int y = _random.Next(Height);


b.SetPixel(x, y, Color.FromName(BrushName[_brushNameIndex]));


}




}






}





2 页面引用：

<asp:Image ID="getcode" src="VerifyCode.aspx" runat="server" />

一般需要同时提供刷新功能(看不清楚换一张)，代码如下

<asp:Image ID="getcode" src="VerifyCode.aspx" runat="server" />  <A href="javascript:getimgcode()">刷新验证码</A>

超链接对应的javascript如下：

<script language="javascript" type="text/javascript">
function getimgcode()
{
var getimagecode = document.getElementById("getcode");
getimagecode.src = "VerifyCode.aspx";
}
</script>

3 判断验证

上述代码是将验证码存贮在Session中，用code来标志。读取代码Session["code"].ToString();
使用中，我们只需要比较Session["code"].ToString()和文本框输入的串(TextBoxCode.Text)是否相同即可进行判断。


if(Session["code"].ToString().Trim().Equals(TextBoxCode.Text.Trim()))




...{




Response.Write("Success");


}
测试通过!