add Element for expressionBuilders for compilation (ASP.NET Settings Schema)

Artigo
11/03/2006

Adds a reference to an expression builder to the collection.

This element is new in the .NET Framework version 2.0.

<add
   expressionPrefix = "prefix" 
   type = "type" 
/>

Attributes and Elements

The following sections describe attributes, child elements, and parent elements.

Attributes

Attribute Description

Attribute	Description
expressionPrefix	Required String attribute. Specifies the prefix for the expression. This string is the left side of an expression as it appears in an .aspx page, for example: `<asp:Label ID="Label1" runat="server" Text="<%$ MyCustomExpression:Hello, world! %>" />` This is the collection key. The default is an empty string ("").
type	Required String attribute. Specifies the name of the expression builder class that handles this expression. This can be a custom class that derives from the ExpressionBuilder class. The default is an empty string ("").

expressionPrefix

Required String attribute.

Specifies the prefix for the expression. This string is the left side of an expression as it appears in an .aspx page, for example:

<asp:Label ID="Label1" runat="server" Text="<%$ MyCustomExpression:Hello, world! %>" />

This is the collection key.

The default is an empty string ("").

type

Required String attribute.

Specifies the name of the expression builder class that handles this expression. This can be a custom class that derives from the ExpressionBuilder class.

The default is an empty string ("").

Child Elements

None.

Parent Elements

Element	Description
configuration	Specifies the root element in every configuration file that is used by the common language runtime and the .NET Framework applications.
system.web	Specifies the root element for the ASP.NET configuration section.
compilation	Configures all compilation settings that ASP.NET uses to compile applications.
expressionBuilders	Defines a collection of resource strings to use during compilation. The resource strings associate prefixes with expression builders. This element is new in the .NET Framework version 2.0.

Remarks

The add element adds a reference to an expression builder to the collection.

The expressionBuilders element defines a collection of resource strings to use during compilation. The resource strings associate prefixes with expression builders.

When the page parser encounters an expression in an .aspx page that is delimited with the string <%$ %>, the parser creates an expression builder for the expression based on the prefix in the string. The prefix is the portion of the string that is to the left of the colon (:). For example, when the parser encounters the string <%$ ConnectionStrings:MessageDB %>, it creates a ConnectionStringsExpressionBuilder object. For more information, see ExpressionBuilder.

Default Configuration

The following default expressionBuilders element is not explicitly configured in the Machine.config file or in the root Web.config file. However, it is the default configuration that is returned by application. Items are added to the expressionBuilders collection in the root Web.config file.

<expressionBuilders>
   <clear />
</expressionBuilders>

The following default expressionBuilders element is configured in the root Web.config file.

<expressionBuilders>
   <add expressionPrefix="Resources" type="System.Web.Compilation.ResourceExpressionBuilder" />
   <add expressionPrefix="ConnectionStrings" type="System.Web.Compilation.ConnectionStringsExpressionBuilder" />
   <add expressionPrefix="AppSettings" type="System.Web.Compilation.AppSettingsExpressionBuilder" />
</expressionBuilders>

Example

The following code example shows how to register a custom expression builder in the Web.config file. A custom expression builder must implement the ExpressionBuilder abstract class.

To reference the expression in an .aspx file, use the following sytax:

<asp:Label ID="Label1" runat="server"

Text="<%$ MyCustomExpression:Hello, world! %>" />

<configuration>
    <system.web>
       <compilation>
          <expressionBuilders>
              <add expressionPrefix="MyCustomExpression"
               type="MyCustomExpressionBuilder"/>
          </expressionBuilders>
       </compilation>
    </system.web>
</configuration>

Element Information

Configuration section handler	CompilationSection
Configuration member	Add
Configurable Locations	Machine.config Root-level Web.config Application-level Web.config Virtual or physical directory–level Web.config
Requirements	Microsoft Internet Information Services (IIS) version 5.0, 5.1, or 6.0 The .NET Framework version 2.0 Microsoft Visual Studio 2003 or Visual Studio 2005

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add Element for expressionBuilders for compilation (ASP.NET Settings Schema)

Attributes and Elements

Attributes

Child Elements

Parent Elements

Remarks

Default Configuration

Example

Element Information

See Also

Tasks

Reference

Concepts

Other Resources

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