Dynamically Loading Master Pages in ASP.Net: Part 1


Introduction

Today most of the websites uses different Master Pages dynamically with a content page depending upon the request. This is very-very useful in two situations as given below. 
  • We can enable the users of our website to customize the appearance of the website by loading different Master Pages. We can display a menu of Master Pages, and allow our users to pick their favorite layout.
  • Another one situation in which loading Master Pages dynamically is useful concerns co-branding or even say different users from different geographical area. Imagine that our company needs to make its website look like a partner website. When users link to our website from the partner website, we don't want users to know that they are traveling to a new website. We can maintain this illusion by dynamically loading different Master Pages based on a query string passed from a partner website. 
Master Page is merged with a content page very early in the page execution life-cycle. This means that we cannot dynamically load a Master Page during the Page_Load() event. The only event during which we can load a Master Page is during the Page PreInit() event that is Pre-Initialization. This is the first event that is raised during the page execution life cycle. 
For example, the given below dynamically loads one of two Master Pages named DynamicMaster1.master and DynamicMaster2.master, here it is.

Code of Default.aspx Page

<%@ Page Title="" Language="VB"MasterPageFile="~/DynamicMaster1.master" %>
<script runat="server">
    Protected Sub Page_PreInit(ByVal sender As Object, ByVal e AsEventArgs)
        If Not Request("master") Is Nothing Then
            Select Case Request("master")
                Case "DynamicMaster1"
                    Profile.MasterPageFile = "DynamicMaster1.master"
                Case "DynamicMaster2"
                    Profile.MasterPageFile = "DynamicMaster2.master"
            End Select
        End If
        MasterPageFile = Profile.MasterPageFile
    End Sub
</script>
<asp:Content
    ID="Content1"
    ContentPlaceHolderID="ContentPlaceHolder1"
    Runat="Server">
    Select a Master Page:
    <ul class="selectMaster">
        <li>
        <a href="Default.aspx?master=DynamicMaster1">DynamicMaster 1</a>
        </li>
        <li>
        <a href="Default.aspx?master=DynamicMaster2">DynamicMaster 2</a>
        </li>
    </ul>

</asp:Content>
 
Code of DynamicMaster1.master Page

<%@ Master Language="VB" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<script runat="server">
</script>
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">

    <style type="text/css">
        html
        {
            background-color:Purple;
        }
        .content
        {
            margin:auto;
            width:700px;
            background-color:Lime;
            padding:10px;
        }
        h1
        {
            border-bottom:solid 4px black;
        }
    </style>

    <title>************YAHOO INTERNATIONAL************</title>
</head>
<body>
    <form id="form1" runat="server">
    <h1>YAHOO INTERNATIONAL !</h1>
    <div id="dynamicms1" class="content">
   
        <asp:ContentPlaceHolder id="ContentPlaceHolder1" runat="server">
       
        </asp:ContentPlaceHolder>
     </div>
    </form>
</body>
</html>



Code of DynamicMaster2.master Page

<%@ Master Language="VB" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<script runat="server">
</script>

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">

    <style type="text/css">
        html
        {
            background-color:Maroon;
        }
        .content
        {
            margin:auto;
            width:700px;
            background-color:Aqua;
            padding:10px;
        }
        h1
        {
            border-bottom:solid 4px black;
        }
    </style>

    <title>************YAHOO INDIA************</title>
</head>
<body>
    <form id="form1" runat="server">
    <h1>YAHOO INDIA !</h1>
    <div id="dynamicms1" class="content">

        <asp:ContentPlaceHolder id="ContentPlaceHolder1" runat="server">
       
        </asp:ContentPlaceHolder>
    </div>
    </form>
</body>
</html>



Code of Web.config File

<?xml version="1.0"?>
<configuration>
                <system.web>
                                <compilation debug="true" targetFramework="4.0"/>
                </system.web>
  <system.web>
    <profile>
      <properties>
        <add
          name="MasterPageFile"
          defaultValue="DynamicMaster1.master" />
      </properties>
    </profile>
  </system.web>
 </configuration>
 
There is some points we have to notice that the page Default.aspx given above includes a Page_PreInit() event handler. This handler grabs the value of the master query string parameter and assigns the value of this parameter to a Profileproperty. Next, the value of the Profile property is assigned to the page's MasterPageFile property. Assigning a value to the MasterPageFile property causes a Master Page to be dynamically loaded. Because the name of the Master Page is assigned to a Profile property, the selected Master Page loads for a user even if the user returns to the website many years in the future. The Profile object automatically persist the values of its properties for a user across multiple visits to a website. The Profile is defined in the web configuration file contained above.

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