Page Life Cycle in ASP.Net and its Events

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

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

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.