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ExpressionBuilder Class

Retrieves a dynamic resource during compilation.

Namespace:  System.Web.Configuration
Assembly:  System.Web (in System.Web.dll)

public sealed class ExpressionBuilder : ConfigurationElement

ASP.NET automatically evaluates expressions during page parsing using the ExpressionBuilder class. The ExpressionBuilderCollection collection, which is made up of the expressionBuilders elements contained in the compilation section of the configuration. The ExpressionBuilder contains specific values in key/value pairs.

A value is retrieved by including an expression of the form

<%$ ExpressionPrefix: ExpressionKey %>

within the page. The ExpressionPrefix maps the type of expression to be retrieved as either a common expression-builder type (that is, AppSettingsExpressionBuilder) or a custom expression builder type. The ExpressionKey specifies the key used to reference the returned value.

If you choose to implement a common expression-builder type, you must map the expression builder to the associated section name in the configuration. If you choose to implement a custom expression-builder type, you must map your expression builder to your custom expression-builder class, which must derive from the ExpressionBuilder class.


Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

.NET Framework

Supported in: 3.5, 3.0, 2.0