Asp.Net母版页元素ID不一致的体现

Asp.Net母版页元素ID不一致的体现
来自森大科技官方博客 http://www.cnsendblog.com/index.php/?p=104
<%@ Page Language="C#" MasterPageFile="~/MasterPage.master" Theme="style" AutoEventWireup="true"
CodeFile="r_Balance.aspx.cs" Inherits="Report_r_Balance" %>
<asp:Content ID="content" ContentPlaceHolderID="MainContent" runat="server">

 <form id="form1" runat="server">
     <div>
         <table class="topTable" cellspacing="0" cellpadding="0" border="0">
             <tbody>
                 <tr class="title">
                     <td>
                         <asp:Label ID="lbPagename" runat="server" SkinID="title" Text="余额统计"></asp:Label>
                     </td>
                 </tr>
                 <tr class="butt">
                     <td>
                         <asp:ImageButton ID="btnPrint" runat="server" SkinID="b_print" OnClick="btnPrint_Click" />
                         <asp:ImageButton ID="btnExport" runat="server" SkinID="b_export" OnClick="btnExport_Click" />
                     </td>
                 </tr>
             </tbody>
         </table>
         <!--结束功能条-->
         <table border="1" >
             <tr>
                                 <td align="center" >
                     卡号*</td>
                 <td colspan="1" >
                     <asp:TextBox ID="txtc_printno" runat="server"></asp:TextBox></td>
                 <td colspan="1" 
                     align="center">
                     <asp:ImageButton ID="nSearch" runat="server" AlternateText="查询" ImageAlign="Middle"
                         ImageUrl="~/images/go.gif" OnClick="nSearch_Click" />
                 </td>
             </tr>
         </table>

....
生成的HTML代码：
<form name="aspnetForm" method="post" action="r_Balance.aspx" id="aspnetForm">
<table class="topTable" cellspacing="0" cellpadding="0" border="0">
<tbody>
<tr class="title">
<td>
<span id="ctl00_MainContent_lbPagename" style="display:inline-block;color:#F2F3F9;border-style:None;font-family:宋体;font-size:13px;height:22px;">余额统计</span>
</td>
</tr>
<tr class="butt">
<td>
<input type="image" name="ctl00$MainContent$btnPrint" id="ctl00_MainContent_btnPrint" src="../App_Themes/style/images/b_print.jpg" align="middle" onclick="return np();" style="border-style:Ridge;border-width:0px;" />
<input type="image" name="ctl00$MainContent$btnExport" id="ctl00_MainContent_btnExport" src="../App_Themes/style/images/b_export.jpg" align="middle" style="border-style:Ridge;border-width:0px;" />
</td>
</tr>
</tbody>
</table>
<!--结束功能条-->
<table border="1" style="font: 宋体; font-size: 12px;">
<tr>

                 <td align="center" >
                     卡号*</td>
                 <td colspan="1" >
                     <input name="ctl00$MainContent$txtc_printno" type="text" id="ctl00_MainContent_txtc_printno"  /></td>
                 <td colspan="1" 
                     align="center">
                     <input type="image" name="ctl00$MainContent$nSearch" id="ctl00_MainContent_nSearch" src="../images/go.gif" alt="查询" align="middle" onclick="return nselect();"  />
                 </td>
             </tr>
         </table>

注意：
1.源文件控件和元素ID和生成HTML文件的ID不一致。在生成的HTML中原ASP控件ID加了ctl00_MainContent_前缀，其他元素加了ctl00$MainContent$前缀。原变form1为aspnetForm这是因为aspx页面的控件是母板页的ContentPlaceHolder
控件下的子控件,所以控件ID会变
2.<system.Web><xhtmlConformance mode="Transitional|Legacy|Strict" />在其中选择 Transitional、Strict则产生自动前缀。ctl00.选择 Legacy|则产生自动前缀_ctl0.
3.后台Request.Form["txtc_name"]键值需要改变，必须变为Request.Form["ctl00$MainContent$txtc_name"]才能收到页面输入值
4.至于为什么，只能说这是.NET机制问题。。。