ASP.
NET Page Life Cycle Overview
Visual Studio 2008
When an ASP.NET page runs, the page goes through a life cycle in which it
performs a series of processing steps. These include initialization,
instantiating controls, restoring and maintaining state, running event handler
code, and rendering. It is important for you to understand the page life cycle
so that you can write code at the appropriate life-cycle stage for the effect
you intend.
If you develop custom controls, you must be familiar with the page life cycle
in order to correctly initialize controls, populate control properties with view-
state data, and run control behavior code. The life cycle of a control is based
on the page life cycle, and the page raises many of the events that you need
to handle in a custom control.
This topic contains the following sections:
General Page Life-Cycle Stages
In general terms, the page goes through the stages outlined in the following
table. In addition to the page life-cycle stages, there are application stages
that occur before and after a request but are not specific to a page. For more
information, see Introduction to the ASP.NET Application Life Cycle and
ASP.NET Application Life Cycle Overview for IIS 7.0.
Some parts of the life cycle occur only when a page is processed as a
postback. For postbacks, the page life cycle is the same during a partial-page
postback (as when you use an UpdatePanel control) as it is during a full-page
postback.
Stage Description
The page request occurs before the page life cycle begins.
When the page is requested by a user, ASP.NET determines
Page request whether the page needs to be parsed and compiled (therefore
beginning the life of a page), or whether a cached version of the
page can be sent in response without running the page.
In the start stage, page properties such as Request and
Response are set. At this stage, the page also determines
Start whether the request is a postback or a new request and sets
the IsPostBack property. The page also sets the UICulture
property.
During page initialization, controls on the page are available
and each control's UniqueID property is set. A master page and
themes are also applied to the page if applicable. If the current
Initialization
request is a postback, the postback data has not yet been
loaded and control property values have not been restored to
the values from view state.
During load, if the current request is a postback, control
Load properties are loaded with information recovered from view
state and control state.
Postback If the request is a postback, control event handlers are called.
After that, the Validate method of all validator controls is called,
event
which sets the IsValid property of individual validator controls
handling
and of the page.
Before rendering, view state is saved for the page and all
controls. During the rendering stage, the page calls the Render
Rendering method for each control, providing a text writer that writes its
output to the OutputStream object of the page's Response
property.
The Unload event is raised after the page has been fully
rendered, sent to the client, and is ready to be discarded. At
Unload
this point, page properties such as Response and Request are
unloaded and cleanup is performed.
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. For control events, you bind the event
handler to the event, either declaratively using attributes such as onclick, or
in code.
Pages also support automatic event wire-up, meaning that ASP.NET looks for
methods with particular names and automatically runs those methods when
certain events are raised. If the AutoEventWireup attribute of the @ Page
directive is set to true, page events are automatically bound to methods that
use the naming convention of Page_event, such as Page_Load and Page_Init.
For more information on automatic event wire-up, see ASP.NET Web Server
Control Event Model.
The following table lists the page life-cycle events that you will use most
frequently. There are more events than those listed; however, they are not
used for most page-processing scenarios. Instead, they are primarily used by
server controls on the ASP.NET Web page to initialize and render themselves.
If you want to write custom ASP.NET server controls, you need to understand
more about these events. For information about creating custom controls,
see Developing Custom ASP.NET Server Controls.
Page Event Typical Use
PreInit Raised 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
IsCallback and 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.
• Read or set profile property values.
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.
Raised after all controls have been initialized and any skin
settings have been applied. The Init event of individual
Init
controls occurs before the Init event of the page.
Use this event to read or initialize control properties.
Raised at the end of the page's initialization stage. Only
one operation takes place between the Init and
InitComplete events: tracking of view state changes is
turned on. View state tracking enables controls to persist
any values that are programmatically added to the
InitComplete ViewState collection. Until view state tracking is turned on,
any values added to view state are lost across postbacks.
Controls typically turn on view state tracking immediately
after they raise their Init event.
Use this event to make changes to view state that you want
to make sure are persisted after the next postback.
Raised after the page loads view state for itself and all
PreLoad controls, and after it processes postback data that is
included with the Request instance.
The Page object calls the OnLoad method on the Page
object, and then recursively does the same for each child
control until the page and all controls are loaded. The Load
Load event of individual controls occurs after the Load event of
the page.
Use the OnLoad event method to set properties in controls
and to establish database connections.
Use these events to handle specific control events, such as
a Button control's Click event or a TextBox control's
TextChanged event.
Note:
Control events
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.
Raised at the end of the event-handling stage.
LoadComplete 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, including child
controls of composite controls. (To do this, the Page object
calls EnsureChildControls for each control and for the
page.)
The Page object raises the PreRender event on the Page
object, and then recursively does the same for each child
control. The PreRender 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.
Raised after each data bound control whose DataSourceID
PreRenderCompl property is set calls its DataBind method. For more
ete information, see Data Binding Events for Data-Bound
Controls later in this topic.
Raised after view state and control state have been saved
SaveStateCompl for the page and for all controls. Any changes to the page
ete or controls at this point affect rendering, but the changes
will not be retrieved on the next postback.
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. However, if your
Render custom control incorporates only standard ASP.NET Web
server controls and no custom markup, you do not need to
override the Render method. For more information, see
Developing Custom ASP.NET Server Controls.
A user control (an .ascx file) automatically incorporates
rendering, so you do not need to explicitly render the
control in code.
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
Unload 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.
Additional Page Life Cycle Considerations
Individual ASP.NET server controls have their own life cycle that is similar to
the page life cycle. For example, a control's Init and Load events occur
during the corresponding page events.
Although both Init and Load recursively occur on each control, they happen
in reverse order. The Init event (and also the Unload event) for each child
control occur before the corresponding event is raised for its container
(bottom-up). However the Load event for a container occurs before the Load
events for its child controls (top-down). When you create a class that inherits
from the Page class, in addition to handling events raised by the page, you
can override methods from the page's base class. For example, you can
override the page's InitializeCulture method to dynamically set culture
information. Note that when an event handler is created using the
Page_event syntax, the base implementation is implicitly called and
therefore you do not need to call it in your method. For example, the base
page class's OnLoad method is always called, whether you create a
Page_Load method or not. However, if you override the page OnLoad method
with the override keyword (Overrides in Visual Basic), you must explicitly call
the base method. For example, if you override the OnLoad method on the
page, you must call base. Load (MyBase.Load in Visual Basic) in order for the
base implementation to be run. For an illustration that shows some of the
most important methods of the Page class that you can override in order to
add code that executes at specific points in the page life cycle, see the .NET
Framework 4 version of this document. (For a complete list of page methods
and events, see the Page class.)
Catch-Up Events for Added Controls
If controls are created dynamically at run time or declaratively within
templates of data-bound controls, their events are initially not synchronized
with those of other controls on the page. For example, for a control that is
added at run time, the Init and Load events might occur much later in the
page life cycle than the same events for controls created declaratively.
Therefore, from the time that they are instantiated, dynamically added
controls and controls in templates raise their events one after the other until
they have caught up to the event during which it was added to the Controls
collection.
Data Binding Events for Data-Bound Controls
To help you understand the relationship between the page life cycle and
data binding events, the following table lists data-related events in data-
bound controls such as the GridView, DetailsView, and FormView controls.
Control Event Typical Use
Raised after the control's PreRender event,
which occurs after the page's PreRender
event. (This applies to controls whose
DataSourceID property is set declaratively.
Otherwise the event happens when you call
DataBinding the control's DataBind method.)
This event marks the beginning of the process
that binds the control to the data. Use this
event to manually open database connections,
if required, and to set parameter values
dynamically before a query is run.
RowCreated (GridView only) Raised after the control's DataBinding event.
or ItemCreated (DataList, Use this event to manipulate content that is
DetailsView, SiteMapPath, not dependent on data binding. For example,
DataGrid, FormView, at run time, you might programmatically add
Repeater, and ListView formatting to a header or footer row in a
controls) GridView control.
Raised after the control's RowCreated or
RowDataBound (GridView ItemCreated event.
only) or ItemDataBound When this event occurs, data is available in
(DataList, SiteMapPath, the row or item, so you can format data or set
DataGrid, Repeater, and the FilterExpression property on child data
ListView controls) source controls in order to display related data
within the row or item.
Raised at the end of data-binding operations in
a data-bound control. In a GridView control,
data binding is complete for all rows and any
child controls.
DataBound Use this event to format data-bound content
or to initiate data binding in other controls that
depend on values from the current control's
content. (For more information, see Catch-Up
Events for Added Controls earlier in this topic.)
Nested Data-Bound Controls
If a child control has been data bound, but its container control has not yet
been data bound, the data in the child control and the data in its container
control can be out of sync. This is true particularly if the data in the child
control performs processing based on a data-bound value in the container
control. For example, suppose you have a GridView control that displays a
company record in each row, and it displays a list of the company officers in
a ListBox control. To fill the list of officers, you would bind the ListBox control
to a data source control (such as SqlDataSource) that retrieves the company
officer data using the company ID in a query.
If the ListBox control's data-binding properties, such as DataSourceID and
DataMember, are set declaratively, the ListBox control will try to bind to its
data source during the containing row's DataBinding event. However, the
CompanyID field of the row does not contain a value until the GridView
control's RowDataBound event occurs. In this case, the child control (the
ListBox control) is bound before the containing control (the GridView control)
is bound, so their data-binding stages are out of sync. To avoid this
condition, put the data source control for the ListBox control in the same
template item as the ListBox control itself, and do not set the data binding
properties of the ListBox declaratively. Instead, set them programmatically
at run time during the RowDataBound event, so that the ListBox control does
not bind to its data until the CompanyID information is available. For more
information, see Binding to Data Using a Data Source Control.
Login Control Events
The Login control can use settings in the Web.config file to manage
membership authentication automatically. However, if your application
requires you to customize how the control works, or if you want to
understand how Login control events relate to the page life cycle, you can
use the events listed in the following table.
Control
Typical Use
Event
Raised during a postback, after the page's LoadComplete event
has occurred. This event marks the beginning of the login
LoggingIn process.
Use this event for tasks that must occur prior to beginning the
authentication process.
Raised after the LoggingIn event.
Authenticat
Use this event to override or enhance the default authentication
e
behavior of a Login control.
Raised after the user name and password have been
authenticated.
LoggedIn Use this event to redirect to another page or to dynamically set
the text in the control. This event does not occur if there is an
error or if authentication fails.
Raised if authentication was not successful.
LoginError Use this event to set text in the control that explains the problem
or to direct the user to a different page.
Concepts
ASP.NET Web Server Control Event Model
Page and Application Context in ASP.NET Web Applications
ASP.NET View State Overview
Binding to Data Using a Data Source Control
Reference
Validating User Input in ASP.NET Web Pages
ASP.NET Login Controls Overview
Other Resources
Developing Custom ASP.NET Server Controls
ASP.NET Page Syntax
Server Event Handling in ASP.NET Web Pages
Change History
Date History Reason
February Improved text and a note about a diagram Customer feedb
2010 available in the .NET 4 version of this document. ack.
Community Content Add
FAQ
Building Controls on PreInit in a Master Page
So the PreInit event is where creates or re-creates dynamic controls. But wha
t if you want to access a control that's already on the page? Well, if you're us
ing the Master Page paradigm, then you'll get a null reference error wheneve
r you try to access a pre-existing control.
The solution to this? Make a call to the Master page before you try to access
the controls, and it will build the master page before building the content pa
ge, and instantiate the controls on your content page. I don't get all the with
ertos and the whyfors, but basically say "object dummy = this.Master" and y
ou'll be able to access controls already on the page during PreInit.
For me, this was incredibly vital information, and I wish it was in a note in the
PreInit section - because unless you're doing 100% dynamic, using PreInit is
almost impossible without that step.
Basic OF .NET
Application: BeginRequest
Application: PreAuthenticateRequest
Application: AuthenticateRequest
Application: PostAuthenticateRequest
Application: PreAuthorizeRequest
Application: AuthorizeRequest
Application: PostAuthorizeRequest
Application: PreResolveRequestCache
Application: ResolveRequestCache
Application: PostResolveRequestCache
Application: PreMapRequestHandler
Page: Construct
Application: PostMapRequestHandler
Application: PreAcquireRequestState
Application: AcquireRequestState
Application: PostAcquireRequestState
Application: PreRequestHandlerExecute
Page: AddParsedSubObject
Page: CreateControlCollection
Page: AddedControl
Page: AddParsedSubObject
Page: AddedControl
Page: ResolveAdapter
Page: DeterminePostBackMode
Page: PreInit
Control: ResolveAdapter
Control: Init
Control: TrackViewState
Page: Init
Page: TrackViewState
Page: InitComplete
Page: LoadPageStateFromPersistenceMedium
Control: LoadViewState
Page: EnsureChildControls
Page: CreateChildControls
Page: PreLoad
Page: Load
Control: DataBind
Control: Load
Page: EnsureChildControls
Page: LoadComplete
Page: EnsureChildControls
Page: PreRender
Control: EnsureChildControls
Control: PreRender
Page: PreRenderComplete
Page: SaveViewState
Control: SaveViewState
Page: SaveViewState
Control: SaveViewState
Page: SavePageStateToPersistenceMedium
Page: SaveStateComplete
Page: CreateHtmlTextWriter
Page: RenderControl
Page: Render
Page: RenderChildren
Control: RenderControl
Page: VerifyRenderingInServerForm
Page: CreateHtmlTextWriter
Control: Unload
Control: Dispose
Page: Unload
Page: Dispose
Application: PostRequestHandlerExecute
Application: PreReleaseRequestState
Application: ReleaseRequestState
Application: PostReleaseRequestState
Application: PreUpdateRequestCache
Application: UpdateRequestCache
Application: PostUpdateRequestCache
Application: EndRequest
Application: PreSendRequestHeaders
Application: PreSendRequestContent
http://www.geekinterview.com/question_details/22673
Diagram available on the .NET Framework 4 version of this page.
The .NET Framework 4 version of this page has a preliminary version of a
new diagram of the page life cycle methods and events. Comments and
suggestions for improving it are welcome.
DataSourceID binding does not always occur before PreRender
Some controls such as repeaters and drop-down lists do not bind until their
PreRender event is called. As a result, they are not bound until after the
page's PreRender event is called. Be safe and just manually DataBind() in
your Page_Load.
See: http://stackoverflow.com/questions/219467/asp-net-repeater-
itemdatabound-happening-after-prerender-event
More Page Events
The article doesn't mention a few events (e.g. Page.PreRenderComplete
Event http://msdn2.microsoft.com/en-
us/library/system.web.ui.page.prerendercomplete.aspx ).
The complete list of page events is here: http://msdn2.microsoft.com/en-
us/library/system.web.ui.page_events.aspx
SILVER - An easy way to remember asp.net lifecycle
S – Start
I – Initialize
L – Load
V – Validate
E – Event Handling
R – Render
http://www.codeproject.com/KB/aspnet/ASPNET_Page_Lifecycle.aspx
How to end session on browser close?
You can kill seesion by calling logout.aspx page on Unload event in
javascript.
Danish Miyan
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Hi I need this in my project..
anyone can help me
