When an ASP.NET is a web page run it goes through a life cycle (various server side events ) in which it performs a series of processing steps. These include initialization, instantiating controls, restoring and maintaining state, running event handler code, and rendering. The following are the various stages or events of ASP.Net page life cycle.

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 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.

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.

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

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.

SaveStateComplete

As the PreRender event is recursively fired for all child controls, this event ensures the completion of the pre-rendering phase.

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.

Summary

To summarize, 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.

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