新建一个AjaxControlToolkitWebSite 项目，把下面的代码复制到你的页面：
<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Default.aspx.cs" Inherits="_Default" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head id="Head1" runat="server">
<title>Untitled Page</title>
</head>
<body>
<form id="form1" runat="server">
<asp:ScriptManager ID="ScriptManager1" runat="server" />
<div>
<ajaxToolkit:FilteredTextBoxExtender ID="FilteredTextBoxExtender1"
runat="server" TargetControlID="TextBox1" FilterType="Numbers">
</ajaxToolkit:FilteredTextBoxExtender>
<ajaxToolkit:FilteredTextBoxExtender ID="FilteredTextBoxExtender2"
runat="server" TargetControlID="TextBox2" FilterType="LowercaseLetters">
</ajaxToolkit:FilteredTextBoxExtender>
<ajaxToolkit:FilteredTextBoxExtender ID="FilteredTextBoxExtender3"
runat="server" TargetControlID="TextBox3" FilterType="Custom, Numbers" ValidChars="+-=/*().">
</ajaxToolkit:FilteredTextBoxExtender>
<table border="0">
<tr>
<td>Only digits are allowed here:</td>
<td>
<asp:TextBox ID="TextBox1" runat="server">
</asp:TextBox>
</td>
</tr>
<tr>
<td>
Only lower-case letters are allowed here:</td>
<td>
<asp:TextBox ID="TextBox2" runat="server">
</asp:TextBox></td>
</tr>
<tr>
<td>
Only math symbols (+,-,*,/,=,.) and numbers:</td>
<td>
<asp:TextBox ID="TextBox3" runat="server"></asp:TextBox></td>
</tr>
</table>
</div>
</form>
</body>
</html>