This blog talks about the ASP.NET application life cycle and page life cycle.

The ASP.NET life cycle could be divided into two groups:

• Application life cycle
• Page life cycle

ASP.NET Application life cycle

The application life cycle has the following stages:

1.      User makes a request for accessing application resource, a page. Browser sends this  request to the web server.

2.      A unified pipeline receives the  first request and the following events take  places:

a)      An object of the class ApplicationManager is created.

b)      An object of the class Hosting Environment is create to provide information regqarding the resources.

c)      Top level items in the  application  are compiled.  

3.      Response objects are created. The application objects such as HttpContext, HttpRequest and HttpResponse are created and initialized.

4.      An  instance of  the HttpApplication object is created and  assigned to the request.

5.      The request is processed by the HttpApplication class. Different events are  raised by this class for processing the  request. 

ASP.NET Page life cycle

When a page is  requested, it is loaded into the  server memory, processed,and sent to  the browser. Then it is unloaded from the memory. At each of these steps, methods and events are variable,which could be overridden according to the  need  of the application.

Following are the different stages of an  ASP.NET Page:

Method                                                                  Description

Page_Init                                                              Page initialization

LoadViewState                                                    View State Loading

LoadPostData                                                      Postback Data processing

Page_load                                                             Page loading

RaisePostDataChangeEvent                               PostBack change Notification

RaisePostBackEvent                                              PostBack event Handling

Page_PreRender                                                      Page Pre  Rendering phase

SaveViewState                                                           View state Saving

Page_Render                                                              Page Rendering

Page_Unload                                                               Page unloading

 PreInit: PreInit is the first event in page life cycle. It checks the postback property and determines whether the page is a postback. It  sets  the  themes and master pages ,creates dynamic control, and gets and sets profiles property values. This event can be handled by overloading the OnPreInit() method or creating a page_Preinit method or creating a Page_PreInit handler.

Init: Init event initializes the  control property and  the  control tree is build. This  event can be  handled by overloading the OnInit() method or creating  a Page_Init handler.

InitComplete: InitComplete event allows tracking of view state. All  the controls turn on view-state tracking.

LoadViewState: LoadViewState event allows loading view state information into the controls.

LoadPostData: During this phase,  the contents of all the input fields are defined with the<form> tag are processed.

Preload: Preload occurs before the post back data is loaded in the  controls. This  event can be handled by  overloading the  onPreLoad method or creating a  Page_preLoad handler.

LoadComplete: The loading process is completed, control event handlers or run, and page validation takes place. This event can be handled by overloading the  OnLoadComplete method or creating a page_LoadComplete handler.

PreRender: The PreRender event occurs just before the output is rendered. By handling this event, pages and controls can perform any updates before the output is rendered.

PreRenderComplete: As the preRender event is recursively fired for all child control, this  event ensures the completion of the pre-rendering phase.

SaveStateComplete: State of control on the page is saved. Personalization, control state and view state information is saved. The HTML markup is generated. This  stage can be handled by overriding the  Render() method or creating a Page_Render Handler.

Unload: The unload phase is  the last phase of the  page life cycle. It raises the  Unload event for all controls recursively and lastly for the page itselfe. Final cleanup is done and all resources and references, such as database connections are freed. This event can be  handled by modified the  OnUnload() method or  creating a page_Unload handler.