ASP.NET Page Life Cycle Events.

Life-Cycle Events

 Within each stage of the life cycle of a page, the page raises events that you can handle to run your own code. 

Page Event	Typical Use
PreInit	Rose after the start stage is complete and before the initialization stage begins. Use this event for the following: Check the IsPostBack property to determine whether this is the first time the page is being processed.  The IsCallbackand, IsCrossPagePostBack properties have also been set at this time. Create or re-create dynamic controls. Set a master page dynamically. Set the Theme property dynamically.  Note If the request is a postback, the values of the controls have not yet been restored from view state. If you set a control property at this stage, its value might be overwritten in the next event.
Init	Rose after all controls has been initialized and any skin settings have been applied.  Use this event to read or initialize control properties.
InitComplete	Raised at the end of the page's initialization stage.
PreLoad	Raised after the page loads view state for itself and all controls, and after it processes postback data that is included with the Request instance.
Load	The Page object calls the OnLoad method on the Page object, occurs after the Load event of the page. Use the OnLoad event method to set properties in controls and to establish database connections.
Control events	Use these events to handle specific control events, such as a Button control's Click event,a TextBox control's TextChangedevent. Note In a postback request, if the page contains validator controls, check the IsValid property of the Page and of individual validation controls before performing any processing.
LoadComplete	Raised at the end of the event-handling stage. Use this event for tasks that require that all other controls on the page be loaded.
PreRender	Raised after the Page object has created all controls that are required in order to render the page,  The Page object raises the PreRender event on the Page object, ThePreRender event of individual controls occurs after the PreRender event of the page. Use the event to make final changes to the contents of the page or its controls before the rendering stage begins.
PreRenderComplete	Raised after each data bound control whose DataSourceID property is set calls its DataBind method.
SaveStateComplete	Raised after view state and control state have been saved for the page and for all controls.
Render	This is not an event; instead, at this stage of processing, the Page object calls this method on each control. All ASP.NET Web server controls have a Render method that writes out the control's markup to send to the browser. If you create a custom control, you typically override this method to output the control's markup. A user control (an .ascx file) automatically incorporates rendering, so you do not need to explicitly render the control in code.
Unload	Raised for each control and then for the page. In controls, use this event to do final cleanup for specific controls, such as closing control-specific database connections. For the page itself, use this event to do final cleanup work, such as closing open files and database connections, or finishing up logging or other request-specific tasks. Note During the unload stage, the page and its controls have been rendered, so you cannot make further changes to the response stream. If you attempt to call a method such as the Response.Write method, the page will throw an exception.