Create and use shared code for Master Page templates

If you don't include the required elements in your code (.master.cs) file in ~/App_Data/PageTemplates (at least MasterPagePageTemplate and TemplateId), the Master Page will be treated as a regular ASP.NET Master Page and won't serve as a C1 CMS template.

However, it will appear in the "Layout" perspective under "Page Templates" / "Shared Code" and can be used as, for example, a master layout for C1 CMS Master Page templates or other purposes.

To use the "shared-code" Master Page as a master layout, follow the standard procedure of using ASP.NET Master Pages:

1. In the Master Page template, specify the "shared-code" master page in the MasterPageFile attribute of the <% @ Master %> directive.
2. Add <asp:content/> controls and map them to the "shared-code" Master Page's content placeholders.
   

   <%@ Master Language="C#" AutoEventWireup="true" 
       MasterPageFile="Common.master" 
       CodeFile="FancyTemplate.master.cs" Inherits="FancyTemplate" %>
   
   <asp:Content ContentPlaceHolderID="phHead" runat="server">
   	<%-- ... --%>
   </asp:Content>
   <asp:Content ContentPlaceHolderID="phContent" runat="server">
   	<%-- ... --%>
   </asp:Content>