A child master page has the file name extension .master, as with any master page. The child master page typically contains content controls that are mapped to content placeholders on the parent master page. In this respect, the child master page is laid out like any content page. However, the child master page also has content placeholders of its own to display content supplied by its own child pages. The following three page listings show a simple nested master page configuration.
This is the parent master file:
C#
<% @ Master Language="C#" %><!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 runat="server"><title>Untitled Page</title>
</head>
<body>
<form id="Form1" runat="server">
<div>
<h1>Parent Master</h1>
<p style="font:color=red">This is parent master content.</p>
<asp:ContentPlaceHolder ID="MainContent" runat="server" />
</div>
</form>
</body>
</html>
VB
<% @ Master Language="VB" %>
<!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" >
<body><head runat="server">
<title>Untitled Page</title></head><form id="Form1" runat="server">
<div><h1>Parent Master</h1><p style="font:color=red">This is parent master content.</p>
<asp:ContentPlaceHolder ID="MainContent" runat="server" />
</div></form></body></html>This is the child master file:C#
<%@ Master Language="C#" MasterPageFile="~/Parent.master"%>
<asp:Content id="Content1" ContentPlaceholderID="MainContent" runat="server">
<asp:panel runat="server" id="panelMain" backcolor="lightyellow">
<h2>Child master</h2>
<asp:panel runat="server" id="panel1" backcolor="lightblue">
<p>This is child master content.</p><asp:ContentPlaceHolder ID="ChildContent1" runat="server" />
</asp:panel>
<asp:panel runat="server" id="panel2" backcolor="pink">
<p>This is child master content.</p><asp:ContentPlaceHolder ID="ChildContent2" runat="server" />
</asp:panel>
<br />
</asp:panel>
</asp:Content>
VB
<%@ Master Language="VB" MasterPageFile="~/Parent.master"%>
<asp:Content id="Content1" ContentPlaceholderID="MainContent" runat="server">
<asp:panel runat="server" id="panelMain" backcolor="lightyellow">
<h2>Child master</h2><asp:panel runat="server" id="panel1" backcolor="lightblue">
<p>This is childmaster content.</p>
<asp:ContentPlaceHolder ID="ChildContent1" runat="server" />
</asp:panel><asp:panel runat="server" id="panel2" backcolor="pink">
<p>This is childmaster content.</p>
<asp:ContentPlaceHolder ID="ChildContent2" runat="server" />
</asp:panel> <br /> </asp:panel></asp:Content>This is a child file that references the child master page:C#
<%@ Page Language="C#" MasterPageFile="~/Child.master"%>
<asp:Content id="Content1" ContentPlaceholderID="ChildContent1" runat="server">
<asp:Label runat="server" id="Label1"
text="Child label1" font-bold="true" />
<br />
</asp:Content>
<asp:Content id="Content2" ContentPlaceholderID="ChildContent2" runat="server">
<asp:Label runat="server" id="Label2"
text="Child label2" font-bold="true"/>
</asp:Content>
VB
<%@ Page Language="VB" MasterPageFile="~/Child.master"%>
<asp:Content id="Content1" ContentPlaceholderID="ChildContent1" runat="server">
<asp:Label runat="server" id="Label1"
text="Child label1" font-bold="true" />
<br></asp:Content><asp:Content id="Content2" ContentPlaceholderID="ChildContent2" runat="server">
<asp:Label runat="server" id="Label2"
text="Child label2" font-bold="true"/>
</asp:Content>