In this article, we will see the stages of execution of the ASP .NET Page.Each request for an .aspx page that hits IIS is handed over to HTTP Pipeline. HTTP Pipeline is a chain of managed objects that sequentially process the request and convert it to plain HTML text content. The start point of HTTP Pipeline is the HttpRuntime class. The ASP.NET infrastructure creates each instance of this class per AppDomain hosted within the worker process. HttpRuntime class picks up an HttpApplication object from an internal pool and sets it to work on the request. It finds out what class has to handle the request. The association between the resources and handlers are stored in the configurable file of the application. In web.config and also in machine.config you will find these lines in <httpHandlers> section.
If you run through the following program, it will be much easier to follow
<add verb="*" path="*.aspx" type="System.Web.UI.PageHandlerFactory"/>
Once viewstate is restored, control will be updated with the client side changes. It loads the posted data values. The PostBackData event gives control a chance to update their state that reflects the state of the HTML element on the client.At the end of the posted data changes event, controls will be reflected with changes done on the client. At this point, load event is fired.Key event in the life cycle is when the server-side code associated with an event triggered on the client. When the user clicks on the button, the page posts back. Page framework calls the RaisePostBackEvent. This event looks up for the event handler and run the associated delegate.After PostBack event, page prepares for rendering. PreRender event is called. This is the place where user can do the update operations before the viewstate is stored and output is rendered. Next stage is saving view state, all the values of the controls will be saved to their own viewstate collection. The resultant viewstate is serialized, hashed, base24 encoded and associated with the _viewstate hidden field.Next the render method is called. This method takes the HtmlWriter object and uses it to accumulate all HTML text to be generated for the control. For each control the page calls the render method and caches the HTML output. The rendering mechanism for the control can be altered by overriding this render method. The final stage of the life cycle is unload event. This is called just before the page object is dismissed. In this event, you can release critical resources you have such as database connections, files, graphical objects etc. After this event browser receives the HTTP response packet and displays the page.