ResizableControlExtender如何用？


<%@ Page Language="C#" AutoEventWireup="true"  CodeFile="Default.aspx.cs" Inherits="_Default" %><%@ Register Assembly="System.Web.Extensions, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35"
    Namespace="System.Web.UI" TagPrefix="asp" %>
<%@ Register Assembly="AjaxControlToolkit, Version=1.0.10920.32880, Culture=neutral, PublicKeyToken=28f01b0e84b6d53e"
    Namespace="AjaxControlToolkit" TagPrefix="cc1" %>
 
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
<html id="Html1" runat="server" xmlns="http://www.w3.org/1999/xhtml" ><head id="Head1" runat="server">
    <title>Untitled Page</title>
    <style type="text/css">
      .handletext{
        width:250px; 
        height:8px;        
        cursor:sn-resize;
     }
     .resizingtext{
        background-color:white; 
        cursor:n-resize;
     }
    </style>
</head>
<body>
    <form id="form2" runat="server">
    
        <asp:ScriptManager ID="ScriptManager2" runat="server">
        </asp:ScriptManager>                     
        <cc1:ResizableControlExtender ID="ResizableControlExtender2" runat="server"
            HandleCssClass="handletext" HandleOffsetY="10" MaximumHeight="1200" MinimumHeight="20"
            TargetControlID="Panel2" >
        </cc1:ResizableControlExtender>
        <asp:Panel ID="Panel2" runat="server" BackColor="#00C000" CssClass="resizingtext"
            Height="342px" Width="306px" style="display: block">
        </asp:Panel>
        
    </form>
</body>
</html>
为何不能拖动大小