HttpCachePolicy.SetETag Method (String)


Sets the ETag HTTP header to the specified string.

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

public void SetETag(
	string etag


Type: System.String

The text to use for the ETag header.

Exception Condition

etag is null.


The ETag header has already been set.

- or -

The SetETagFromFileDependencies has already been called.

The ETag header is a unique identifier for a specific version of a document. It is used by clients to validate client-cached content to avoid requesting it again. Once an ETag header is set, subsequent attempts to set it fail and an exception is thrown.

SetETag is introduced in the .NET Framework version 3.5. For more information, see .NET Framework Versions and Dependencies.

The following code example demonstrates how to set the ETag header to a custom value.


.NET Framework
Available since 1.1
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