ASP.NET (4) - Life Cycle

This series of articles is about ASP.NET. They are from my previous years, legacy notes on OneNote. Reviewing the concepts may be helpful even for our current programming because they have a lot of similar features, such as Angular, React, and these modern "laguanges".

• ASP.NET (1) --- ASP and ASP.NET
• ASP.NET (2) --- ASP.NET Controls
• ASP.NET (3) --- User/Custom Controls
• ASP.NET (4) - Life Cycle --- this article
  • ASP,NET (4-1) - Page Life Cycle: Debugging 

A. Introduction

This article will discuss the life cycle of an ASP.NET page associated with the Application Life Cycle and Control Life Cycle.

• A - Introduction
• B - ASP.NET Page Life Cycle Overview
• C - Server Events Processing and Sequence
• D - ASP.NET Application Life Cycle
• E - Life Cycle of a Mobile Web Forms Page
• F - Control Execution Lifecycle (.NET 1.1)

B. ASP.NET Page Life Cycle Overview

Following are the different phases of the Page Life Cycle:

Roughly

• Start: Initialization
  • Init events of controls and then
  • The page
• Load
  • Load view state,
  • Load the page and then
  • Load each child's controls
• Even Handling
  • Postback handling,
  • Validation, and
  • Other events handling
• Render
  • Save view state and
  • Render each controls and
  • The page
• Unload: Clean up such as
  • Data connection or
  • Opened files

Shown as:

ASP.NET Page Life Cycle Overview

C. Server Events Processing and Sequence

• Server Control Events:
  • Post-back events (posting events)
    • Cause the Web page to be sent back to the server for immediate processing, such as
      • Button,
      • LinkButton,
      • ImageButton).
  • Cached events 
    • Saved in the page’s view state to be processed when a post-back event occurs, such as:
      • TextBox,
      • DropDownList,
      • ListBox,
      • RadioButton and
      • CheckBox).
  • Validation events:
    • Handled on the page without posting back or caching, such as
      • Validators
• Server Control Events Sequence:
  1. The client-side validation events are processed before the page is post back.
  2. The server-side validation events are processed first on the server.
  3. Then cached events;
  4. Then post-back event.

D. ASP.NET Application Life Cycle

1. Application Start
   • The webserver executes the application start when a user requests an application for access. In this method, it sets all global variables to default.
2. Object Creation
   • Object creation holds all the HTTP Context, HTTP Request, and HTTP Response by the webserver. It also contains information about the request, cookies, and browsing information.
3. HTTP Application
   • HTTP Application is an object created by the webserver. It helps to process all the subsequent information that is sent to the user.
4. Dispose
   • Dispose is an event that is called before the application is destroyed. It also helps to release manually unmanaged resources when the objects are no longer needed.
5. Application End
   • Application End is the last stage of the application life cycle. It helps to unload the memory. 

E. Life Cycle of a Mobile Web Forms Page
 

Stage	Page Event	Overridable method
Page initialization	Init
View state loading	LoadViewState
Postback data processing	LoadPostData method in any control that implements the IPostBackDataHandler interface
Page loading	Load
Postback change notification	aisePostDataChangedEvent method in any control that implements the IPostBackDataHandler interface
Postback event handling	Any postback event defined by controls	RaisePostBackEvent method in any control that implements the IPostBackEventHandler interface
Page pre-rendering phase	PreRender
View state saving	SaveViewState
Page rendering	Render
Page unloading	Unload

F. Control Execution Lifecycle (.NET 1.1)
 

Phase	What a control needs to do	Method or event to override
Initialize	Initialize settings needed during the lifetime of the incoming Web request (e.g, get application.path). See Handling Inherited Events.	Init event (OnInit method)
Load view state	At the end of this phase, the ViewState property of a control is automatically populated as described in Maintaining State in a Control. A control can override the default implementation of the LoadViewState method to customize state restoration.	LoadViewState method
Process postback data	Process incoming form data and update properties accordingly. See Processing Postback Data. Note   Only controls that process postback data participate in this phase.	LoadPostData method (if IPostBackDataHandler is implemented)
Load	Perform actions common to all requests, such as setting up a database query. At this point, server controls in the tree are created and initialized, the state is restored, and form controls reflect client-side data. See Handling Inherited Events.	Load event (OnLoad method)
Send postback change notifications	Raise change events in response to state changes between the current and previous postbacks. See Processing Postback Data. Note   Only controls that raise postback change events participate in this phase.	RaisePostDataChangedEvent method (if IPostBackDataHandler is implemented)
Handle postback events	Handle the client-side event that caused the postback and raise appropriate events on the server. See Capturing Postback Events. Note   Only controls that process postback events participate in this phase.	RaisePostBackEvent method (if IPostBackEventHandler is implemented)
Prerender	Perform any updates before the output is rendered. Any changes made to the state of the control in the prerendering phase can be saved, while changes made in the rendering phase are lost. See Handling Inherited Events.	PreRender event (OnPreRender method)
Save state	The ViewState property of a control is automatically persisted to a string object after this stage. This string object is sent to the client and back as a hidden variable. To improve efficiency, a control can override the SaveViewState method to modify the ViewState property. See Maintaining State in a Control.	SaveViewState method
Render	Generate output to be rendered to the client. See Rendering an ASP.NET Server Control.	Render method
Dispose	Perform any final cleanup before the control is torn down. References to expensive resources, such as database connections, must be released in this phase. See Methods in ASP.NET Server Controls.	Dispose method
Unload	Perform any final cleanup before the control is torn down. Control authors generally perform cleanup in Dispose and do not handle this event.	UnLoad event (On UnLoad method)

References

• ASP.NET Page Life Cycle Overview
• Control Execution Lifecycle | Microsoft Learn
• Control execution lifecycle