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HttpResponse.AddOnSendingHeaders(Action<HttpContext>) Method


Registers a callback that the ASP.NET runtime will invoke immediately before response headers are sent for this request.

 System::Web::ISubscriptionToken ^ AddOnSendingHeaders(Action<System::Web::HttpContext ^> ^ callback);
public System.Web.ISubscriptionToken AddOnSendingHeaders (Action<System.Web.HttpContext> callback);
member this.AddOnSendingHeaders : Action<System.Web.HttpContext> -> System.Web.ISubscriptionToken
Public Function AddOnSendingHeaders (callback As Action(Of HttpContext)) As ISubscriptionToken



The callback method.


An ISubscriptionToken object that represents the subscription to the OnSendingHeaders pseudo-event.



The AddOnSendingHeaders method is not invoked if the native module flushes the response first.

The pseudo-event OnSendingHeaders differs from the IHttpModule-level pipeline event in that it is a per-request subscription rather than a per-application subscription. The intent is that the callback may modify the response status code or may set a response cookie or header. Other usage notes and caveats:

  • This method is effective only when IIS runs in integrated pipeline mode pipeline and only if response headers haven't yet been sent for the current request.

  • The ASP.NET runtime does not guarantee anything about the thread that the callback is invoked on. For example, the callback may be invoked synchronously in a background thread if a background flush is being performed. Current is not guaranteed to be available in such a thread.

  • The callback must not call any method that manipulates the response entity body or that results in a flush. For example, the callback must not call Redirect, as that method may manipulate the response entity body.

  • The callback must contain only short-running synchronous code. Attempting to invoke an asynchronous operation or wait on such an operation could result in a deadlock.

  • The callback must not throw an exception; otherwise behavior is undefined.

Applies to