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Src/nprt_plugin/gecko/1.8/win/idl/nsIPrefBranch2.idl

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+/* -*- Mode: IDL; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* ***** BEGIN LICENSE BLOCK *****
+ * Version: NPL 1.1/GPL 2.0/LGPL 2.1
+ *
+ * The contents of this file are subject to the Netscape Public License
+ * Version 1.1 (the "License"); you may not use this file except in
+ * compliance with the License. You may obtain a copy of the License at
+ * http://www.mozilla.org/NPL/
+ *
+ * Software distributed under the License is distributed on an "AS IS" basis,
+ * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
+ * for the specific language governing rights and limitations under the
+ * License.
+ *
+ * The Original Code is Mozilla Communicator client code.
+ *
+ * The Initial Developer of the Original Code is 
+ * Netscape Communications Corporation.
+ * Portions created by the Initial Developer are Copyright (C) 1998
+ * the Initial Developer. All Rights Reserved.
+ *
+ * Contributor(s):
+ * Alec Flett <alecf@netscape.com>
+ * Brian Nesse <bnesse@netscape.com>
+ * Benjamin Smedberg <benjamin@smedbergs.us>
+ *
+ * Alternatively, the contents of this file may be used under the terms of
+ * either the GNU General Public License Version 2 or later (the "GPL"), or 
+ * the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
+ * in which case the provisions of the GPL or the LGPL are applicable instead
+ * of those above. If you wish to allow use of your version of this file only
+ * under the terms of either the GPL or the LGPL, and not to allow others to
+ * use your version of this file under the terms of the NPL, indicate your
+ * decision by deleting the provisions above and replace them with the notice
+ * and other provisions required by the GPL or the LGPL. If you do not delete
+ * the provisions above, a recipient may use your version of this file under
+ * the terms of any one of the NPL, the GPL or the LGPL.
+ *
+ * ***** END LICENSE BLOCK ***** */
+
+#include "nsIPrefBranch.idl"
+
+interface nsIObserver;
+
+/**
+ * nsIPrefBranch2 allows clients to observe changes to pref values.
+ *
+ * @status FROZEN
+ * @see nsIPrefBranch
+ */
+[scriptable, uuid(74567534-eb94-4b1c-8f45-389643bfc555)]
+interface nsIPrefBranch2 : nsIPrefBranch
+{
+  /**
+   * Add a preference change observer. On preference changes, the following
+   * arguments will be passed to the nsIObserver.observe() method:
+   *   aSubject - The nsIPrefBranch object (this)
+   *   aTopic   - The string defined by NS_PREFBRANCH_PREFCHANGE_TOPIC_ID
+   *   aData    - The preference which has changed
+   *
+   * @param aDomain   The preference on which to listen for changes. This can
+   *                  be the name of an entire branch to observe.
+   *                  e.g. Holding the "root" prefbranch and calling
+   *                  addObserver("foo.bar.", ...) will observe changes to
+   *                  foo.bar.baz and foo.bar.bzip
+   * @param aObserver The object to be notified if the preference changes.
+   * @param aHoldWeak true  Hold a weak reference to |aObserver|. The object
+   *                        must implement the nsISupportsWeakReference
+   *                        interface or this will fail.
+   *                  false Hold a strong reference to |aObserver|.
+   *
+   * @note
+   * Registering as a preference observer can open an object to potential
+   * cyclical references which will cause memory leaks. These cycles generally
+   * occur because an object both registers itself as an observer (causing the
+   * branch to hold a reference to the observer) and holds a reference to the
+   * branch object for the purpose of getting/setting preference values. There
+   * are 3 approaches which have been implemented in an attempt to avoid these
+   * situations.
+   * 1) The nsPrefBranch object supports nsISupportsWeakReference. Any consumer
+   *    may hold a weak reference to it instead of a strong one.
+   * 2) The nsPrefBranch object listens for xpcom-shutdown and frees all of the
+   *    objects currently in its observer list. This insures that long lived
+   *    objects (services for example) will be freed correctly.
+   * 3) The observer can request to be held as a weak reference when it is
+   *    registered. This insures that shorter lived objects (say one tied to an
+   *    open window) will not fall into the cyclical reference trap.
+   *
+   * @see nsIObserver
+   * @see removeObserver
+   */
+  void addObserver(in string aDomain, in nsIObserver aObserver,
+                   in boolean aHoldWeak);
+
+  /**
+   * Remove a preference change observer.
+   *
+   * @param aDomain   The preference which is being observed for changes.
+   * @param aObserver An observer previously registered with addObserver().
+   *
+   * @see nsIObserver
+   * @see addObserver
+   */
+  void removeObserver(in string aDomain, in nsIObserver aObserver);
+};
+
+%{C++
+
+/**
+ * Notification sent when a preference changes.
+ */
+#define NS_PREFBRANCH_PREFCHANGE_TOPIC_ID "nsPref:changed"
+
+%}