The ASP.NET page framework is a scalable programming model
that you can use on the server to dynamically generate Web pages. The ASP.NET
page framework is the successor to Active Server Pages. This article address
the following page framework topics:
Page Life Cycle
Because the page framework is a stateless a and disconnected
model, every time a client requests an .aspx page, many things occur during the
page processing to make the process appear seamless to the client. It is
important for you to know and to understand this staged execution sequence when
you work with ASP.NET.
For more information about the page life
cycle, refer to the following .NET Framework Software Development Kit (SDK)
documentation:
Page Events
During the life cycle of an ASP.NET page, a few standard events
that are exposed from the
Page object are used frequently. The ASP.NET page framework
automatically connects to (or wires up) appropriate delegate instances at run
time for these methods. This saves you from having to write the necessary "glue
code." The following list presents the delegate instances that are wired up at
run time in the order in which they are fired:
- Page_Init: During this event, you can initialize values or connect any
event handlers that you may have.
- Page_Load: During this event, you can perform a series of actions to either
create your ASP.NET page for the first time or respond to client-side events
that result from a post. The page and control view state have been restored
prior to this event. Use the IsPostBack page property to check whether this is the first time that the
page is being processed. If it is the first time, perform data binding. Also,
read and update control properties.
- Page_DataBind: The DataBind event is raised when the DataBind method is called at the page level. If you call DataBind on individual controls, it only fires the DataBind event of the controls beneath it.
- Page_PreRender: The PreRender event is fired just before the view state is saved and the
controls are rendered. You can use this event to perform any last minute
operations on your controls.
- Page_Unload: After a page has finished rendering, the Page_Unload event fires. This event is a good place to perform final cleanup
work. This includes items such as the cleanup of open database connections,
discarding objects, or closing those files that are open.
The following list outlines the events that are
non-deterministic:
- Page_Error: If an unhandled exception occurs during page processing, the Error event fires. The Error event gives you an opportunity to gracefully handle
errors.
- Page_AbortTransaction: Transaction events are useful if you want to indicate whether a transaction
succeeds or fails. This event is commonly used for shopping cart scenarios in
which this event can indicate the success or failure of an order. This event
fires when a transaction has been aborted.
- Page_CommitTransaction: This event fires when a transaction has been committed
successfully.
The following code samples illustrate a declaration for the
Page_Load event.
Visual C# .NET and Visual J# .NET
public void Page_Load()
{
if (!Page.IsPostback){
//Do something.
}
}
Public Sub Page_Load()
If Not Page.IsPostBack Then
'Do something.
End If
End Sub
For more information about the page events, refer to the following .NET
Framework SDK documentation:
For an overview of programming with these page events and server
control events, refer to the following .NET Framework SDK documentation:
Page Directives
Page directives specify optional settings that the Page Compiler
uses when it processes files. Page directives are located at the top of a page
file and use the following syntax:
<%@ directive {attribute=value}* %>
ASP.NET pages support the following directives:
- @ Page
- @ Implements
- @ Import
- @ Register
- @ Assembly
- @ Reference
- @ OutputCache
Each directive in turn supports one or more attribute-value
pairs, which are not case-sensitive.
For more information about the
page directives, refer to the following .NET Framework SDK documentation:
Inline Versus Code-Behind Programming Models
ASP.NET supports two modes of page development:
- Page logic code that is written inside <script
runat=server> blocks within an .aspx file and dynamically compiled the first
time the page is requested on the server.
- Page logic code that is written within an external class
that is compiled prior to deployment on a server and linked "behind" the .aspx
file at run time.
For additional information about
inline and code-behind programming models, click the article number below to
view the article in the Microsoft Knowledge Base:
303247 INFO: ASP.NET Code-Behind Model Overview