ASP.NET Page Life Cycle
A page in an ASP.NET application consists of several server controls. These
are the fundamental building blocks of an ASP.NET application. The Life cycle of
an ASP.NET page, depends on whether the page is requested for the first
time or it is a postback. Postback is a process by which a page can
request for itself.
When the Page is requested for the first time
The Life Cycle of a page when requested for the first time:
Initializing: During this phase, the server creates an instance of the server
control
Loading: During this phase, the instance of the control is loaded onto the
page object in which it is defined.
PreRendering: During this phase, the control is updated with the changes made
to it. This prepares the control for rendering.
Saving: During this phase, the state information of the control is saved. For
example, if a value is set for the control during the Load event, it is embedded
in the HTML tag that will be returned to the browser.
Rendering: During this phase, the server creates the corresponding HTML tag
for the control.
Disposing: During this phase, all cleanup tasks, such as
closing files and database connections opened by the control are performed.
Unloading: During this phase, all cleanup tasks, such as
destroying the instances of server control are performed. This is the final
event in the life cycle of a server control
Life cycle when the page processed during a postback event
The processing sequence in which a page is processed during a postback event
is:
Initializing: During this phase, the server creates an instance of the server
control
Loading view state: During this phase, the view state of the
control posted by the client is reloaded into the new instance of the control.
Loading: During this phase, the instance of the control is loaded onto the
page object in which it is defined.
Loading the postback data: During this phase, the server
searches any data corresponding to the control that is loaded in the data posted
by the client.
PreRendering: During this phase, the control is updated with the changes made
to it. This prepares the control for rendering.
Saving state: During this phase, the change in the state of
control between the current request and the previous request of the page is
saved. For each change, the corresponding event is raised. For example, if the
text of a textbox is changed, the new text is saved and a text_change event is
raised.
Rendering: During this phase, the server creates the corresponding HTML tag
for the control.
Disposing: During this phase, all cleanup tasks, such as
closing files and database connections opened by the control are performed.
Unloading: During this phase, all cleanup tasks, such as
destroying the instances of server control are performed. This is the final
event in the life cycle of a server control
The events associated with the relevant page cycle phases are:
Page Initialization: Page_Init
View State Loading:LoadViewState
Postback data processing: LoadPostData
Page Loading: Page_Load
PostBack Change Notification: RaisePostDataChangedEvent
PostBack Event Handling: RaisePostBackEvent
Page Pre Rendering Phase: Page_PreRender
View State Saving: SaveViewState
Page Rendering: Page_Render
Page Unloading: Page_UnLoad
The following figure illustrates how the server controls on an ASP.NET page
is processed by the server:
|
