Thursday 29 March 2012

ASP.NET Master Pages


Master Pages in Asp.Net

Definition:
ASP.NET master pages allow us to create a consistent layout for the pages in our application.  A single master page defines the look and feel and standard behavior that we want for all of the pages or a group of pages in our application.  We can then create individual content pages that contain the content we want to display.  When we request the content pages, they merge with the master page to produce output that combines the layout of the master page with the content from the content page.

Working of Master Page:
Master pages actually consists two pieces, one is the master page itself and other is one or more content pages.

Master Pages – A master page is an ASP.NET file with the extension .master (eg:  Example.master) with a predefined layout that can include static text, HTML elements, and server controls.  The master page is identified by a special directive, “@Master that replaces the “@Pagedirective that is used for ordinary .aspx pages.  See the below how the directive looks like.

<%@ Master Language="C#" %>

The “@Masterdirective can contain most of the same directives that a “@Controldirective can contain.  For example, see the following master-page directive which includes the name of a code-behind file, and assigns a class name to the master page.

<%@ Master Language="C#" CodeFile="MasterPage.master.cs" Inherits="MasterPage" %>

In addition to the “@Masterdirective, the master page also contains all of the top-level HTML elements for a page, such as html, head, and form.  For example, in a master page we might use an HTML table for the layout, an img element for our company logo, static text for the copyright notice, and server controls to create standard navigation for our site.  We can use any HTML and any ASP.NET elements as part of our master page.

Replaceable Content Placeholders:
The master page also includes one or more “ContentPlaceHolder” controls in addition to static text and controls that will appear on all pages.  These placeholder controls define regions where the replaceable content will appear.  In turn, the replaceable content is defined in content pages.  After we defined the ContentPlaceHolder controls, a master page might look like the following.

<%@ 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>Master page title</title>
</head>
<body>
    <form id="form1" runat="server">
        <table>
           <tr>
               <td><asp:contentplaceholder id="Main" runat="server" /></td>
               <td><asp:contentplaceholder id="Footer" runat="server" /></td>
           </tr>
        </table>
    </form>
</body>
</html>

Content Pages:

We can define the content for the master page's placeholder controls by creating individual content pages, which are ASP.NET pages (.aspx files and, optionally, code-behind files) that are bound to a specific master page.  The binding is established in the content page's @Page directive by including a “MasterPageFile” attribute which points to the master page to be used.
For example, a content page might have the following @Page directive, which binds it to the Master1.master page.

<%@ Page Language="C#" MasterPageFile="~/MasterPages/Master1.master" Title="Content Page"%>

In the content page, we can create the content by adding Content controls and mapping them to ContentPlaceHolder controls on the master page.
For example, the master page might have content placeholders called Main and Footer.  In the content page, we can create two Content controls, one that is mapped to the ContentPlaceHolder control, “Mainand the other mapped to the ContentPlaceHolder control “Footer, as shown in the following figure.



After creating Content controls, we can add text and controls to them.  In a content page, anything that is not inside the Content controls except script blocks for server code results in an error.  We can perform any tasks in a content page that we do in an ASP.NET page.
For example, we can generate content for a Content control using server controls and database queries or other dynamic mechanisms.

See below for how the content page might look like.
 
<% @ Page Language="C#" MasterPageFile="~/Master.master" Title="Content Page 1" %>
<asp:Content ID="Content1" ContentPlaceHolderID="Main" Runat="Server">
    Main content.
</asp:Content>
    
<asp:Content ID="Content2" ContentPlaceHolderID="Footer" Runat="Server" >
    Footer content.
</asp:content>

The @Page directive binds the content page to a specific master page, and it defines a title for the page that will be merged into the master page.  Note that the content page contains no other markup outside of the Content controls.  (The master page must contain a “head element with the attribute runat="server" so that the title setting can be merged at run time.

Note:  We can create multiple master pages to define different layouts for different parts of our site, and a different set of content pages for each master page.

Advantages:
·         They allow us to centralize the common functionality of our pages so that we can make updates in just one place.
·         They make it easy to create one set of controls and code and apply the results to a set of pages.  For example, we can use controls on the master page to create a menu that applies to all pages.
·         They give us fine-grained control over the layout of the final page by allowing us to control how the placeholder controls are rendered.
·         They provide an object model that allows us to customize the master page from individual content pages.

Run-time Behavior of Master Pages:
At run time, master pages are handled in the following sequence:
1.       Users request a page by typing the URL of the content page.
2.       When the page is fetched, the @Page directive is read.  If the directive references a master page, the master page is read as well.  If this is the first time the pages have been requested, both pages are compiled.
3.       The master page with the updated content is merged into the control tree of the content page.
4.       The content of individual Content controls is merged into the corresponding ContentPlaceHolder control in the master page.
5.       The resulting merged page is rendered to the browser.

Master Page and Content Page Paths:
When a content page is requested, its content is merged with the master page, and the page runs in the context of the content page.
For example, if you get the CurrentExecutionFilePath property of the HttpRequest object, whether in content page code or in master page code, the path represents the location of the content page.
The master page and content page do not have to be in the same folder.  As long as the MasterPageFile attribute in the content page's @Page directive resolves to a .master page, ASP.NET can merge the content and master pages into a single rendered page.

Referencing External Resources:

Both the content page and master page can contain controls and elements that reference external resources.
For example, both might contain image controls that reference image files, or they might contain anchors that reference other pages.
The context for the merged content and master pages is that of the content page.  This can affect how you specify URLs for resources, such as image files and target pages, in anchors.

Server Controls:

In server controls on master pages, ASP.NET dynamically modifies the URLs of properties that reference external resources.
For example, we might put an Image control on a master page and set its ImageUrl property to be relative to the master page.  At run time, ASP.NET will modify the URL so that it resolves correctly in the context of the content page.
ASP.NET can modify URLs in the following cases:
·         The URL is a property of an ASP.NET server control.
·         The property is marked internally in the control as being a URL. (The property is marked with the attribute UrlPropertyAttribute.) In practical terms, ASP.NET server control properties that are commonly used to reference external resources are marked in this way.

Other Elements:

ASP.NET cannot modify URLs on elements that are not server controls.
For example, if we use an img element on a master page and set its src attribute to a URL, ASP.NET will not modify the URL.  In that case, the URL will be resolved in the context of the content page and create the URL accordingly.
In general, when working with elements on master pages, it is recommended that we use a server control, even for elements that do not require server code.
For example, instead of using an img element, use an Image server control.  In that way, ASP.NET can resolve URLs correctly and you can avoid maintenance issues that might arise if we move the master or content page.

Master Pages and Themes:
We cannot directly apply an ASP.NET theme to a master page.  If we add a theme attribute to the @Master directive, the page will raise an error when it runs.
However, themes are applied to master pages under these circumstances:
·         If a theme is defined in the content page.  Master pages are resolved in the context of content pages, so the content page's theme is applied to the master page as well.
·         If the whole site is configured to use a theme by including a theme definition in the pages Element (ASP.NET Settings Schema) element.

Scoping Master Pages:
We can attach content pages to a master page at three levels:
At the page levelWe can use a page directive in each content page to bind it to a master page, as following.
<%@ Page Language="C#" MasterPageFile="Example.Master" %>
At the application levelBy making a setting in the pages element of the application's configuration file (Web.config), we can specify that all ASP.NET pages (.aspx files) in the application automatically bind to a master page, as following.
<pages masterPageFile="Example.Master" />
At the folder levelThis strategy is like binding at the application level, except that we make the setting in a Web.config file in one folder only. The master-page bindings then apply to the ASP.NET pages in that folder.

1 comment:

  1. can i knw , how to include notepad,or word or calculator appliaction , without creating them , i mean how to use applications which are already present in system

    ReplyDelete