Introduction
In ASP.NET 1.1, to give your application a coherent style you were using user controls to make one footer and one header, maybe you make one menu, then you drop those controls into each and every new page you add to your application, it's somehow a good way to make a consistent maintainable UI. Master Pages is an easier solution!
What are Master Pages ?
Master pages let you make a consistent layout for your application, you can make one master page that holds the layout/look & feel and common functionality of your whole application and upon this master page, you can build all the other pages, we call these pages Content Pages. So simply you can build your master page and then build content pages, and while creating the content pages you bind them to the master page you have created before, those two pages are merged at runtime to give you the rendered page.
Master Pages and ContentPlaceHolders
The master page has the extension .master and it's actually an aspx page but with the directive <%@ Master Language="C#"%>, instead of the standard page directive, almost the attributes of the Master directive are the same as that of the page, you can add any kind of controls the same as you design aspx pages, and it's advisable to use the menu control at your master page.Every MasterPage should include at least one ContentPlaceHolder, this control is a placeholder for the content that will be merged at runtime, noting that the content page is just an aspx standard page but you should supply the attribute MasterPageFile to the page directive to bind the content page to the master page.
<%@ Page Language="C#" MasterPageFile="~/MasterPages/MyLayout.master"%>
Content Server Control
Inside the content pages you will find one Content server control added by default, actually when you add controls you add them to the content server control.
The attribute ContentPlaceHolderID is very important as it decides what content will be bound to which ContentPlaceHolder on the master page, this is a nice way to decide the location of where the contents will be displayed; so this way you can have multiple content on one content page and also multiple ContentPlaceHolders on the master page.
One Important Note: The content pages don't include the common tags as Body, Head,etc. Remember that, that was the same with user controls, as after merging, there should be only one Body and Head tags.
Creating Master Page
As you see, the attributes of the Master directive is common to the ones of the Page directive, and they are self-descriptive; CodeFile is the path of the code behind file. It can be VB or C#, note that in one Web Site you can mix between both languages. Inherits decides the class within the code file to be used. Language is the language of the code behind file.
AutoEventWireup is so important; for any page there is an automatic way to bind the events to methods in the same aspx file or in code behind, if this attribute is true . Page events are automatically bound to methods that are using naming convention as Page_event, for example Page_Load, Page_Init, and Page_PreInit (this is the event fired before creating the controls of the page). This has one disadvantage that the standard events of the page should adhere to this naming convention, but if you set it to false, it will give you more flexibility to use any names for the event handlers, here we should remember the importance of Handles keyword in VB.NET
This server control is the most important for the master pages as this is the zone in which the content pages will be rendered.
8. Switch to the Design of the master page, you will get the ContentPlaceHolder1 shown, now you can design the master page just as any aspx page, so for this practice we'll do a simple master page.
9. From Layout menu select Insert Table, Select Template option, then select Header , footer and side, then drag the ContentPlaceHolder1 control into the right middle cell of the table you have just added. Add one label into the left middle cell,
10. Double click anywhere at the master page. This will open the code behind and will add the Page_Load event handler. You can write the following code:
Label1.Text = "The Time of Server is: " + DateTime.Now.TimeOfDay;
This will show the time of the server at the label.
Creating Content Page
The content page is just one aspx page but you bind this page to one master page while you are creating it. To do this, right click your web application from solution explorer and select Add New Item, select Web Form from the installed templates and check Select Maser Page, enter the name of the new page as myContentPage.aspx
Because you have checked the Select Master Page box, you will get the following dialog to select one master page, this will bind the new aspx page to the selected master page
The page you have just added will open in source view and you will find one entry. Add the MasterPageFile attribute set to the value of the master page file you have selected before. This should be assigned the value ~/MyLayOut.master. You will also find one Content server control added by default and the attribute ContentPlaceHolderID assigned to ContentPlaceHolder1. This is the default value which refers to the ContentPlaceHolder control at the master page and if you have renamed this control at the master page, you should change it now to the correct ID. This sets the zone in which this content page will be shown as we said before.
Switch to the design view of myContentPage.aspx. You will get the following figure which shows all the master page contents added by all the contents of the master page is dim because they are not editable, only the Content1 will be enabled if you click the white area, and you can now add any controls just as you do for any aspx page.
Double click the white area of Content1, you will get the event handler of Page_Load, add the following line:
Label1.Text = this.MasterPageFile;
This will show the path of the Master Page file into the label. Actually you can get a reference to the Master Page from a content page by using the Master property which refers to the page's master page, furthermore you can refer to any control on the master page by using this.Master.FindControl(string id), this method takes the Id of the control on the master page and returns Control object, so you should cast to the data type of the control.
From all this we can say Master Pages are a great addition to ASP.NET 2.0, it's a good way to templatize your application. And you can access the master page from child content pages by using this Master.
I hope you will be confident about the Master Pages after reading this artical.
Happy Coding .......
Love ASP.NET
