Development and Programming
C# and .NET
Understanding ASP.NET Page Life Cycle
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.
<asp:Button ID="btnSubmit1" runat="server" OnClick="btnSubmit_Click" sText="Submit" />
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.
<%@ Page Language="C#" AutoEventWireup="true" Inherits="MyWebApp.EventWireUpTrue" %>
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.
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.
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 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 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 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 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.
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.
Use this event for tasks that require that all other controls on the page be loaded.
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 property is set calls its DataBind method. For more information, see Data Binding Events for Data-Bound Controls later in this topic.
Raised after view state and control state have been saved for the page and for all controls. Any changes to the page 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 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 finishing up logging or other request-specific tasks.
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
The following illustration 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. (For a complete list of page methods and events, see the Page class.) The illustration also shows how these methods relate to page events and to control events. The sequence of methods and events in the illustration is from top to bottom, and within each row from left to right.
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, 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.
The application Pools element contains configuration settings for all application pools running on your Internet Information Services (IIS) 7 server or above. An application pool defines a group of one or more worker processes, configured with common settings that serve requests to one or more applications that are assigned to that application pool. Because application pools allow a set of Web applications to share one or more similarly configured worker processes, they provide a convenient way to isolate a set of Web applications from other Web applications on the server computer. Process boundaries separate each worker process; therefore, application problems in one application pool do not affect Web sites or applications in other application pools. Application pools significantly increase both the reliability and manageability of your Web infrastructure.
You can choose to use the default application pool provided by IIS on install, or you can create your own application pool. You can run as many application pools on your IIS 7 server as you need, though this can affect server performance. Application pools can contain one or more worker processes. Each worker process represents work being done for a Web site, Web application, or Web service. You can create a Web garden by enabling multiple worker processes to run in a single application pool.
In IIS 7, each application pool uses one of two .NET integration modes for running ASP.NET applications: Integrated or Classic. The .NET integration mode defined for the application pool determines how IIS processes an incoming request to the sites, applications and Web services that run in that application pool.
Types of Application Pools
There are two types of application pools
1) Integrated (default)
Integrated mode allows IIS to process requests in the application pool by using the IIS 7 integrated pipeline. This allows ASP.NET modules to participate in IIS request processing regardless of the type of resource requested. Using integrated mode makes available features of the ASP.NET 2.0 request pipeline available to requests for static content, as well as ASP, PHP and other content types. By default, IIS 7 application pools run in this mode.
Classic mode uses the IIS 6.0 processing pipeline for hosting ASP.NET applications. In this mode, requests are processed initially through IIS 7 modules, and ASP.NET requests are further processed by the aspnet_isapi.dll. The ASP.NET processing pipeline is separate from the IIS 7 processing pipeline, and the ASP.NET request processing pipeline features are not available to other resource types. This also means that an ASP.NET request must pass through authentication and authorization modules in both process models. While this is not as efficient as Integrated mode, it does allow you to run applications developed using ASP.NET version 1.1 on an IIS 7 server without modifying the application to run in Integrated mode.
PreInit fires before the page instantiates its controls, so any control in the page doesn't exist yet and null will be returned if you try to reference to a control. But you can go directly to the Request.Form collection where controls will post new values there.
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