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@ Page

Updated: February 2010

Defines page-specific (.aspx file) attributes used by the ASP.NET page parser and compiler.

<%@ Page attribute="value" [attribute="value"...] %>

Async

Makes the page an asynchronous handler (that is, it causes the page to use an implementation of IHttpAsyncHandler to process requests).

The default is false.

AsyncTimeOut

Defines the time-out interval (in seconds) used when processing asynchronous tasks. The default is 45 seconds.

The value must be an integer.

For more information, see the AsyncTimeout property.

AspCompat

When set to true, allows the page to be executed on a single-threaded apartment (STA) thread. This allows the page to call STA components, such as a component developed with Microsoft Visual Basic 6.0. Setting this attribute to true also allows the page to call COM+ version 1.0 components that require access to unmanaged Active Server Pages (ASP) built-in objects. These are accessible through the ObjectContext object or the OnStartPage method. The default is false.

NoteNote:

Setting this attribute to true can cause your page's performance to degrade. For more information, see the Remarks section.

AutoEventWireup

Indicates whether the page's events are autowired. true if event autowiring is enabled; otherwise, false. The default is true. For more information, see ASP.NET Web Server Control Event Model.

Buffer

Determines whether HTTP response buffering is enabled. true if page buffering is enabled; otherwise, false.

The default is true.

ClassName

A string that specifies the name of the page class that will be dynamically compiled when the page is requested. This value can be any valid class name and can include a fully qualified class name. If a value for this attribute is not specified, the class name for the compiled page is based on the page's file name and uses the default namespace ASP. If a value for the ClassName attribute is specified without a full namespace, then the namespace ASP is used, combined with the specified class name to create a fully qualified class name.

Another page can reference the class name assigned to the first page by using the @ Reference directive.

NoteNote:

It is possible in the code-behind page class to reference members of the associated .aspx page class using the fully qualified class name for the .aspx page. However, if you precompile your site with source protection enabled, the code-behind page class is not located in the same assembly as the .aspx page class. Therefore the class reference in the code-behind file will not work. For more information on precompilation, see ASP.NET Precompilation Overview.

ClientTarget

Indicates the target user agent (typically, a Web browser such as Microsoft Internet Explorer) for which ASP.NET server controls should render content. This value can be any valid alias as defined within the <clientTarget> section of the application's configuration file. For more information, see the ClientTarget property.

CodeBehind

Specifies the name of the compiled file that contains the class that is associated with the page. This attribute is not used at run time.

This attribute is used for Web application projects. The CodeFile attribute is used for Web site projects. For more information about Web project types in Visual Studio, see Web Site File Types and Web Application Projects Overview.

CodeFile

Specifies a path to the referenced code-behind file for the page. This attribute is used together with the Inherits attribute to associate a code-behind source file with a Web page. The attribute is valid only for compiled pages.

This attribute is used for Web site projects. The CodeBehind attribute is used for Web application projects. For more information about Web project types in Visual Studio, see Web Site File Types and Web Application Projects Overview.

CodeFileBaseClass

Specifies the type name of a base class for a page and its associated code-behind class. This attribute is optional, but when it is used the CodeFile attribute must also be present. Use this attribute when you want to implement a shared scenario, where you define common fields (and optionally, associated events) in a base class to reference the controls declared in a Web page. Because of the ASP.NET code generation model, if you defined the fields in a base class without using this attribute, at compile time new member definitions would be generated for the controls declared in the Web page (within a separate partial class stub), and your desired scenario would not work. But if you use the CodeFileBaseClass attribute to associate the base class with the page, and you make your partial class (its name is assigned to the Inherits attribute and its source file is referenced by the CodeFile attribute) inherit from the base class, then the fields in the base class will be able to reference the controls on the page after code generation.

CodePage

Indicates the value of the encoding scheme used for the response. The value is an integer that serves as an ID for the encoding scheme. For a list of possible CodePage IDs, see the Encoding class.

CompilationMode

Sets whether the page should be compiled, using a string that specifies one of several enumerated options. The default value is Always, so .aspx pages are compiled by default. For details, see the CompilationMode enumeration.

CompilerOptions

A string containing compiler options used to compile the page. In C# and Visual Basic, this is a sequence of compiler command-line switches. For more information about compiler options, see C# Compiler Options or Visual Basic Compiler.

ContentType

Defines the HTTP content type of the response as a standard MIME type. Supports any valid HTTP content-type string. For a list of possible values, search for MIME in the MSDN Library.

Culture

Indicates the culture setting for the page. The value of this attribute must be a valid culture ID. Note that the LCID and Culture attributes are mutually exclusive; if you use one of these attributes, you cannot use the other in the same page. For more information, see the Culture property and the CultureInfo class.

Debug

Indicates whether the page should be compiled with debug symbols. true if the page should be compiled with debug symbols; otherwise, false. Because this setting affects performance, you should only set the attribute to true during development.

Description

Provides a text description of the page. This value is ignored by the ASP.NET parser.

EnableEventValidation

Enables validation of events in postback and callback scenarios. true if events are being validated; otherwise, false. The default is true.

Page event validation reduces the risk of unauthorized postback requests and callbacks. When the enableEventValidation property is set to true, ASP.NET allows only the events that can be raised on the control during a postback request or callback. With this model, a control registers its events during rendering and then validates the events during the post-back or callback handling. All event-driven controls in ASP.NET use this feature by default.

It is strongly recommended that you do not disable event validation. Before disabling event validation, you should be sure that no postback could be constructed that would have an unintended effect on your application.

EnableSessionState

Defines session-state requirements for the page. true if session state is enabled; ReadOnly if session state can be read but not changed; otherwise, false. The default is true. These values are case-insensitive. For more information, see ASP.NET Session State Overview.

EnableTheming

Indicates whether themes are used on the page. true if themes are used; otherwise, false. The default is true.

EnableViewState

Indicates whether view state is maintained across page requests. true if view state is maintained; otherwise, false. The default is true.

For more information, see the Control.EnableViewState property.

EnableViewStateMac

Indicates that ASP.NET should verify message authentication codes (MAC) in the page's view state when the page is posted back from the client. true if view state should be MAC checked; otherwise, false. The default is true.

NoteNote:

A view-state MAC is an encrypted version of the hidden variable that a page's view state is persisted to when sent to the browser. When you set this attribute to true, the encrypted view state is checked to verify that it has not been tampered with on the client. For security reasons, assure that the EnableViewStateMac attribute is set to true as by default..

ErrorPage

Defines a target URL for redirection if an unhandled page exception occurs. For more information, see the ErrorPage property.

Explicit

Determines whether the page is compiled using the Visual Basic Option Explicit mode. true indicates that the Visual Basic explicit compile option is enabled and that all variables must be declared using a Dim, Private, Public, or ReDim statement; otherwise, false. The default is false.

NoteNote:

This attribute is ignored by languages other than Visual Basic. Also, this option is set to true in the Machine.config configuration file. For more information, see Machine Configuration Files and ASP.NET Configuration Files.

Inherits

Defines a code-behind class for the page to inherit. This can be any class derived from the Page class. This attribute is used with the CodeFile attribute, which contains the path to the source file for the code-behind class. The Inherits attribute is case-sensitive when using C# as the page language, and case-insensitive when using Visual Basic as the page language.

If the Inherits attribute does not contain a namespace, ASP.NET checks whether the ClassName attribute contains a namespace. If so, ASP.NET attempts to load the class referenced in the Inherits attribute using the namespace of the ClassName attribute. (This assumes that the Inherits attribute and the ClassName attribute both use the same namespace.)

For more information about code-behind classes, see ASP.NET Web Page Code Model.

Language

Specifies the language used when compiling all inline rendering (<% %> and <%= %>) and code declaration blocks within the page. Values can represent any .NET Framework-supported language, including Visual Basic, C#, or JScript. Only one language can be used and specified per page.

LCID

Defines the locale identifier for the Web Forms page.

NoteNote:

The locale identifier is a 32-bit value that uniquely defines a locale. ASP.NET uses the default locale of the Web server unless you specify a different locale for a Web Forms page by using this attribute. Note that the LCID and Culture attributes are mutually exclusive; if you use one of these attributes, you cannot use the other in the same page. For more information about locales, search the MSDN Library.

LinePragmas

Determines whether the runtime should generate line pragmas in the source code. These are compiler options that are often used by debugging tools to mark specific locations in a source file. true if line pragmas should be generated; otherwise, false.

MaintainScrollPositionOnPostback

Indicates whether to return the user to the same position in the client browser after postback. true if users should be returned to the same position; otherwise, false. The default is false.

NoteNote:

Developers can define this attribute for all pages by setting the maintainScrollPostitionOnPostback attribute (note that it is case-sensitive in configuration files) on the <pages> element of the Web.config file.

MasterPageFile

Sets the path to the master page for the content page or nested master page. Supports relative and absolute paths. For more information, see the MasterPageFile property.

ResponseEncoding

Indicates the name of the encoding scheme used for the HTTP response that contains a page's content. The value assigned to this attribute is a valid encoding name. for a list of possible encoding names, see the Encoding class. You can also call the GetEncodings method for a list of possible encoding names and IDs.

SmartNavigation

Indicates whether the page supports the smart navigation feature of Internet Explorer 5.5 or later. true if smart navigation is enabled; otherwise, false. The default is false.

In ASP.NET version 2.0 and later versions, the SmartNavigation property is obsolete. Use the SetFocus method and the MaintainScrollPositionOnPostback property instead.

Src

Specifies a path to a source file containing code that is linked to the page. In the linked source file, you can choose to include programming logic for your page either in a class or in code declaration blocks.

You can use the Src attribute to link build providers to the page. For more information, see the BuildProvider class. Also, in versions of ASP.NET prior to 2.0, the Src attribute was used as an alternative way to link a code-behind file to a page. In ASP.NET 2.0, the preferred approach to linking a code-behind source file to a page is to use the Inherits attribute to specify a class, along with the CodeFile attribute to specify the path to the source file for the class.

Strict

Indicates that the page should be compiled using the Visual Basic Option Strict mode. true if Option Strict is enabled; otherwise, false. The default is false.

NoteNote:

This attribute is ignored by languages other than Visual Basic.

StyleSheetTheme

Specifies a valid theme identifier to use on the page. When the StyleSheetTheme attribute is set, individual controls can override the stylistic settings contained in a theme. Thus a theme can provide an overall look for a site, while the settings contained in the StyleSheetTheme attribute enable you to customize particular settings on a page and its individual controls.

TargetSchema

Specifies the name of a schema that validates content on the page. This serves only a descriptive purpose; no actual validation is performed, and the attribute is ignored by the parser.

Theme

Specifies a valid theme identifier to use on the page. When the Theme attribute is set without using the StyleSheetTheme attribute, it overrides individual style settings on controls, enabling you to create a unified and consistent look on a page. For more information, see the Theme property.

Title

Specifies a title for the page that is rendered within the HTML <title> tags in the response. The title can also be accessed programmatically as a property of the page. For details, see the Title property.

Trace

Indicates whether tracing is enabled. true if tracing is enabled; otherwise, false. The default is false. For more information, see ASP.NET Tracing Overview and the Trace property.

TraceMode

Indicates how trace messages are to be displayed for the page when tracing is enabled. Possible values are SortByTime and SortByCategory. The default, when tracing is enabled, is SortByTime. For more information about tracing, see ASP.NET Tracing Overview.

Transaction

Indicates whether COM+ transactions are supported on the page. Possible values are Disabled, NotSupported, Supported, Required, and RequiresNew. The default is Disabled.

UICulture

Specifies the user interface (UI) culture setting to use for the page. Supports any valid UI culture value. For more information, see the UICulture property.

ValidateRequest

Indicates whether request validation should occur. If true, request validation checks all input data against a hard-coded list of potentially dangerous values. If a match occurs, an HttpRequestValidationException exception is thrown. The default is true.

This feature is enabled in the machine configuration file (Machine.config). You can disable it in your application configuration file (Web.config) or on the page by setting this attribute to false.

NoteNote:

This functionality helps reduce the risk of cross-site scripting attacks for straightforward pages and ASP.NET applications. An application that does not properly validate user input can suffer from many types of malformed input attacks, including cross-site scripting and Microsoft SQL Server injection attacks. There is no substitute for carefully evaluating all forms of input in an application and making sure that they are either properly validated or encoded, or that the application is escaped prior to manipulating data or sending information back to the client.

ViewStateEncryptionMode

Determines how view state is encrypted, with three possible enumerated values: Auto, Always, or Never. The default is Auto, meaning that view state will be encrypted if an individual control requests it. For more information, see the ViewStateEncryptionMode enumeration.

WarningLevel

Indicates the compiler warning level at which you want the compiler to treat warnings as errors, thus aborting compilation of the page. Possible warning levels are 0 through 4. For more information, see the WarningLevel property.

This directive can be used only in Web Forms pages. You can include only one @ Page directive per .aspx file. Further, you can define only one Language attribute per @ Page directive, because only one language can be used per page. Because the most commonly used default values are supplied for most of the attributes, either in the source code or in configuration files, it is often unnecessary to add a large set of attributes to the directive. Generally, you should add the minimal set of attributes required to specify the features you want for a page. If there is a common attribute that you want to apply to all pages, for example if you want to enable tracing on all pages, consider enabling the feature in the Web.config file rather than adding the Trace attribute to every individual page.

NoteNote:

The @ Page directive has a number of attributes in common with other directives that apply to an entire source file, such as the @ Control directive (used in .ascx files for Web user controls) and the @ Master directive (used in .master files for master pages).

To define multiple attributes for the @ Page directive, separate each attribute/value pair with a single space. For a specific attribute, do not include a space on either side of the equal sign (=) that connects the attribute with its value. For an example, see the Example section of this topic.

Smart navigation is an ASP.NET feature supported in Internet Explorer 5.5 and later browsers. It allows a page to be refreshed while maintaining scroll position and element focus between navigations, causing only a single page to be stored in the browser's history, and without the common flicker associated with refreshing a Web page. Smart navigation is best used with ASP.NET pages that require frequent postbacks but with visual content that does not change dramatically on return. Consider this carefully when deciding whether to set this attribute to true.

When the AspCompat attribute is set to true for a page, if you use a constructor to create a COM component before the request is scheduled, it will run on a multithreaded apartment (MTA) thread. Doing this causes significant Web server performance degradation. To avoid this problem, create COM components only from within one of the Page events (such as Page_Load, Page_Init, and so on) or one of the Page methods. Be sure as well that the objects are not created at page construction time.

The following code example demonstrates the recommended way to create an instance of a COM object in a page with AspCompat enabled.

<%@ Page AspCompat="true" language="C#" %>
<script runat="server" >

MyComObject comObj;

public void Page_Load(){
   // Use comObj here when the code is running on the STA thread pool.
   comObj = New MyComObject();
   // Do something with the combObj object.
}
NoteNote:

Adding an @ Master directive to a master page does not allow you to use the same directive declaration in pages that depend on the master. Instead, use the pages element to define page directives globally.

The following code example instructs the ASP.NET page compiler to use Visual Basic as the server-side code language for the page, and sets the default HTTP MIME ContentType attribute transmitted to the client to "text/xml".

<%@ Page Language="VB" ContentType="text/xml" %>

Date

History

Reason

February 2010

Corrections to CodeBehind and CodeFile attribute descriptions.

Content bug fix.

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