经常在论坛里看到有问怎么实现验证码的帖子,其实关于验证码的文章在CSDN,DEV-CLUB等
网站上都有很多,但是很多文章只讲诉了如何输出一个随机生成数字或字符的图象,当然了,这个是验证码的核心了,但是对很多ASP.NET的初学者来说,怎么使用它生成的图象又成了一个问题(论坛有不少问这个的),这也是我写本文的一个原因.
言归正传,关于验证码的原理,我就不多说了,大家可以参见其他文章,文末附有完整的实例代码,里面有详细的注释,你可以跳过解说文字,直接使用
首先,我要简要说说Session和ViewState的用法,因为后面会用到它
把数据存储在Session中:Session("key")="test"
从Session取值:dim testvalue as string=Session("key")
类似的:
把数据存储在ViewState中:ViewState("key")="test"
从ViewState中取值:dim testvalue as string=ViewState("key")
关于ViewState的更详细的资料,你可以参看MSDN的<<ASP.NET ViewState 初探>>一文
百闻不如一见,有时代码本身就比任何解说更有表现力,所以在此就不对代码解说太多了,本文实现的验证码需要用到两个文件:
gif.aspx 该文件用于生成验证码
ValidateCode.aspx 该文件用来测试验证码(即如何使用)
下面给出gif.aspx的完整代码:
<%@ import namespace="System"%>
<%@ import namespace="System.io"%>
<%@ import namespace="System.Drawing"%>
<%@ import namespace="System.Drawing.Imaging"%>
<script language="vb" runat="server">
Sub Page_Load(Sender as object,e as eventargs)
'RndNum是一个自定义函数
dim VNum as string=RndNum(4)
Session("VNum")=VNum
ValidateCode(VNum)
End Sub
'生成图象验证码函数
Sub ValidateCode(VNum)
Dim Img as System.Drawing.Bitmap
Dim g as Graphics
Dim ms as MemoryStream
dim gheight as integer=Int(Len(VNum)*11.5)
'gheight为图片宽度,根据字符长度自动更改图片宽度
img=new BitMap(Gheight,20)
g=Graphics.FromImage(img)
g.DrawString(VNum,(New Font("Arial",10)),(New SolidBrush(color.blue)),3,3)'在矩形内绘制字串(字串,字体,画笔颜色,左上x.左上y)
ms=New MemoryStream()
img.Save(ms,ImageFormat.Png)
Response.ClearContent() '需要输出图象信息 要修改HTTP头
Response.ContentType="image/Png"
Response.BinaryWrite(ms.ToArray())
g.Dispose()
img.Dispose()
Response.End()
End Sub
'--------------------------------------------
'函数名称:RndNum
'函数参数:VcodeNum--设定返回随机字符串的位数
'函数功能:产生数字和字符混合的随机字符串
Function RndNum(VcodeNum)
dim Vchar as string="0,1,2,3,4,5,6,7,8,9,A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,W,X,Y,Z"
dim VcArray() as string=split(Vchar,",") '将字符串生成数组
dim VNum as string=""
dim i as byte
For i=1 to VcodeNum
Randomize
VNum=VNum & VcArray(Int(35*Rnd)) '数组一般从0开始读取,所以这里为35*Rnd
Next
Return VNum
End Function
</script>
那么又应该如何使用该文件生成的图象验证码,看这句代码:
<asp:Image id="Image1" runat="server" ImageUrl="gif.aspx" />
这就是用来显示验证码的Image控件,你可以把它放在任何你喜欢的地方,下面的给出详细的使用代码,你把它保存为ValidateCode.aspx,并把它和gif.aspx放在同一目录下,在浏览器中打开ValidateCode.aspx,就可以测试它的效果了:
<script language="vb" Runat="Server">
Sub Page_Load(Sender as object,e as eventargs)
dim VNum as string=Session("VNum")
Session.Abandon()
ViewState("VNum")=VNum
End Sub
'下面的事件代码是用来测试验证码,可以根据需要更改
Sub btnSubmit_click(sender as object,e as eventargs)
'判断输入的验证码与所给是否相同
If txtValidateCode.text=Cstr(ViewState("VNum")) then
lblShow.text="<font color='red'>提示:验证通过</font>"
Else
lblShow.text="所填写的验证码与所给的不符"
End If
End Sub
</script><br><html><br><body><br><form runat="server"><br> <div align="center"><br> <table width="750"><br> <!--DWLayoutTable--><br> <tr> <br> <td width="256" height="46">&nbsp; </td><br> <td width="9">&nbsp;</td><br> <td width="88">&nbsp;</td><br> <td width="87">&nbsp;</td><br> <td width="100">&nbsp;</td><br> <td width="68">&nbsp;</td><br> <td width="97">&nbsp;</td><br> </tr><br> <tr> <br> <td height="21"></td><br> <td></td><br> <td colspan="3" valign="top"><asp:label ID="lblShow" runat="server"></asp:label></td><br> <td>&nbsp;</td><br> <td>&nbsp;</td><br> </tr><br> <tr> <br> <td height="14"></td><br> <td></td><br> <td></td><br> <td></td><br> <td></td><br> <td></td><br> <td></td><br> </tr><br> <tr> <br> <td height="21">&nbsp;</td><br> <td colspan="2" valign="middle">验证码:</td><br> <td valign="top"><asp:Image id="Image1" runat="server" ImageUrl="gif.aspx" /></td><br> <td>&nbsp;</td><br> <td>&nbsp;</td><br> <td>&nbsp;</td><br> </tr><br> <tr> <br> <td height="20">&nbsp;</td><br> <td colspan="2" valign="top">输入验证码:</td><br> <td valign="top"><asp:textbox ID="txtValidateCode" runat="server" TextMode="SingleLine" /></td><br> <td colspan="2" valign="middle"><font color="#FF0000" size="2">*注意:区分大小写</font></td><br> <td>&nbsp;</td><br> </tr><br> <tr> <br> <td height="25">&nbsp;</td><br> <td>&nbsp;</td><br> <td>&nbsp;</td><br> <td>&nbsp;</td><br> <td>&nbsp;</td><br> <td>&nbsp;</td><br> <td>&nbsp;</td><br> </tr><br> <tr> <br> <td height="19">&nbsp;</td><br> <td>&nbsp;</td><br> <td>&nbsp;</td><br> <td valign="top"><asp:button ID="btnSubmit" runat="server" Text="比较" onclick="btnSubmit_click" /></td><br> <td>&nbsp;</td><br> <td>&nbsp;</td><br> <td>&nbsp;</td><br> </tr><br> </table><br> </div><br></form><br></body><br></html><br></div>
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