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ASP.NET Life Cycle Overview

When an ASP.NET page runs, the page goes through a life cycle in which it performs a series of processing steps. These include initialization, instantiating controls, restoring and maintaining state, running event handler code, and rendering. It is important for you to understand the page life cycle so that you can write code at the appropriate life-cycle stage for the effect you intend.

If you develop custom controls, you must be familiar with the page life cycle in order to correctly initialize controls, populate control properties with view-state data, and run control behavior code. The life cycle of a control is based on the page life cycle, and the page raises many of the events that you need to handle in a custom control.

This topic contains the following sections:


1.General Page Life-cycle Stages

2.Life-cycle Events

3.Additional Page Life Cycle Considerations

4.Catch-Up Events for Added Controls

5.Data Binding Events for Data-Bound Controls


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 this steps, methods and events are available, which could be overridden according to the need of the application. In other words, you can write your own code to override the default code.

The Page class creates a hierarchical tree of all the controls on the page. All the components on the page, except the directives are part of this control tree. You can see the control tree by adding trace= "true" to the Page directive. We will cover page directives and tracing under 'directives' and 'error handling'.

The page life cycle phases are:

  • Initialization

  • Instantiation of the controls on the page

  • Restoration and maintenance of the state

  • Execution of the event handler codes

  • Page rendering

Understanding the page cycle helps in writing codes for making some specific thing happen at any stage of the page life cycle. It also helps in writing custom controls and initializing them at right time, populate their properties with view-state data and run control behavior code.

When an ASP.NET page runs, the page goes through a life cycle in which it performs a series of processing steps. These include initialization, instantiating controls, restoring and maintaining state, running event handler code, and rendering. It is important for you to understand the page life cycle so that you can write code at the appropriate life-cycle stage for the effect you intend.

If you develop custom controls, you must be familiar with the page life cycle in order to correctly initialize controls, populate control properties with view-state data, and run control behavior code. The life cycle of a control is based on the page life cycle, and the page raises many of the events that you need to handle in a custom control.


Following are the different stages of an ASP.Net page:

  • Page request . when ASP.Net gets a page request, it decides whether to parse and compile the page or there would be a cached version of the page; accordingly the response is sent

  • Starting of page life cycle . at this stage, the Request and Response objects are set. If the request is an old request or post back, the IsPostBack property of the page is set to true. The UICulture property of the page is also set.

  • Page initialization . at this stage, the controls on the page are assigned unique ID by setting the UniqueID property and themes are applied. For a new request postback data is loaded and the control properties are restored to the view-state values.

  • Page load . at this stage, control properties are set using the view state and control state values.

  • Validation . Validate method of the validation control is called and if it runs successfully, the IsValid property of the page is set to true.

  • Postback event handling . if the request is a postback (old request), the related event handler is called.

  • Page rendering . at this stage, view state for the page and all controls are saved. The page calls the Render method for each control and the output of rendering is written to the OutputStream class of the Page's Response property.

  • Unload . the rendered page is sent to the client and page properties, such as Response and Request are unloaded and all cleanup done.

ASP.Net Page Life Cycle Events:

At each stage of the page life cycle, the page raises some events, which could be coded. An event handler is basically a function or subroutine, bound to the event, using declarative attributes like Onclick or handle.

Following are the page life cycle events:

  • PreInit . PreInit is the first event in page life cycle. It checks the IsPostBack property and determines whether the page is a postback. It sets the themes and master pages, creates dynamic controls and gets and sets profile property values. This event can be handled by overloading the OnPreInit method or creating a Page_PreInit handler.

  • Init . Init event initializes the control property and the control tree is built. 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 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.

  • Load . the Load event is raised for the page first and then recursively for all child controls. The controls in the control tree are created. This event can be handled by overloading the OnLoad method or creating a Page_Load handler.

  • LoadComplete . the loading process is completed, control event handlers are 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 controls, 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 itself. Final cleanup is done and all resources and references, such as database connections, are freed. This event can be handled by modifying the OnUnLoad method or creating a Page_UnLoad handler.

  • Individual ASP.NET server controls have their own life cycle that is similar to the page life cycle. For example, a control's Init and Load events occur during the corresponding page events.


    Although both Init and Load recursively occur on each control, they happen in reverse order. The Init event (and also the Unload event) for each child control occur before the corresponding event is raised for its container (bottom-up). However the Load event for a container occurs before the Load events for its child controls (top-down). Master pages behave like child controls on a page: the master page Init event occurs before the page Init and Load events, and the master page Load event occurs after the page Init and Load events.


    When you create a class that inherits from the Page class, in addition to handling events raised by the page, you can override methods from the page's base class. For example, you can override the page's InitializeCulture method to dynamically set culture information. Note that when an event handler is created using the Page_event syntax, the base implementation is implicitly called and therefore you do not need to call it in your method. For example, the base page class's OnLoad method is always called, whether you create a Page_Load method or not. However, if you override the page OnLoad method with the override keyword (Overrides in Visual Basic), you must explicitly call the base method. For example, if you override the OnLoad method on the page, you must call base.Load (MyBase.Load in Visual Basic) in order for the base implementation to be run.


    The following illustration shows some of the most important methods of the Page class that you can override in order to add code that executes at specific points in the page life cycle. (For a complete list of page methods and events, see the Page class.) The illustration also shows how these methods relate to page events and to control events. The sequence of methods and events in the illustration is from top to bottom, and within each row from left to right.



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