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 these 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 'event 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.
Following are the different stages of an The Official Microsoft ASP.NET Site page:
Page request - When The Official Microsoft ASP.NET Site 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 the 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 on its successful execution, 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 invoked.
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 Response property of page.
Unload - The rendered page is sent to the client and page properties, such as Response and Request, are unloaded and all cleanup done.
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