Preconditions are specified by the client in the request-header fields and are evaluated on the Web server. For example, by using preconditions, clients can prevent a requested method (for example, GET) from being applied to a resource other than the one intended. For more information, see section 14, "Header Field Definitions," in the Hypertext Transfer Protocol -- HTTP/1.1 specification on the World Wide Web Consortium (W3C) Web site.

The OnExecuteUrlPreconditionFailure method is called when preconditions prevent the DefaultHttpHandler object from processing a request. A deriving class might override the OnExecuteUrlPreconditionFailure method to throw an exception when the preconditions fail. The DefaultHttpHandler does not throw an exception in the OnExecuteUrlPreconditionFailure method.

Any of the following will cause the preconditions to fail:

• Calling HttpResponse..::.Write.

• Calling HttpResponse..::.AddHeader.

• Calling HttpResponse..::.Flush.

• Changing the cache policy for the response.

• Adding a Stream object as a filter to the HttpResponse..::.Filter property.

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

.NET Framework

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