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/gecko_sdk/idl/nsIPrefBranch2.idl

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  1/* -*- Mode: IDL; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
  2/* ***** BEGIN LICENSE BLOCK *****
  3 * Version: MPL 1.1/GPL 2.0/LGPL 2.1
  4 *
  5 * The contents of this file are subject to the Mozilla Public License Version
  6 * 1.1 (the "License"); you may not use this file except in compliance with
  7 * the License. You may obtain a copy of the License at
  8 * http://www.mozilla.org/MPL/
  9 *
 10 * Software distributed under the License is distributed on an "AS IS" basis,
 11 * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
 12 * for the specific language governing rights and limitations under the
 13 * License.
 14 *
 15 * The Original Code is Mozilla Communicator client code.
 16 *
 17 * The Initial Developer of the Original Code is
 18 * Netscape Communications Corporation.
 19 * Portions created by the Initial Developer are Copyright (C) 1998
 20 * the Initial Developer. All Rights Reserved.
 21 *
 22 * Contributor(s):
 23 *   Alec Flett <alecf@netscape.com>
 24 *   Brian Nesse <bnesse@netscape.com>
 25 *   Benjamin Smedberg <benjamin@smedbergs.us>
 26 *
 27 * Alternatively, the contents of this file may be used under the terms of
 28 * either the GNU General Public License Version 2 or later (the "GPL"), or
 29 * the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
 30 * in which case the provisions of the GPL or the LGPL are applicable instead
 31 * of those above. If you wish to allow use of your version of this file only
 32 * under the terms of either the GPL or the LGPL, and not to allow others to
 33 * use your version of this file under the terms of the MPL, indicate your
 34 * decision by deleting the provisions above and replace them with the notice
 35 * and other provisions required by the GPL or the LGPL. If you do not delete
 36 * the provisions above, a recipient may use your version of this file under
 37 * the terms of any one of the MPL, the GPL or the LGPL.
 38 *
 39 * ***** END LICENSE BLOCK ***** */
 40
 41#include "nsIPrefBranch.idl"
 42
 43interface nsIObserver;
 44
 45/**
 46 * nsIPrefBranch2 allows clients to observe changes to pref values.
 47 *
 48 * @status FROZEN
 49 * @see nsIPrefBranch
 50 */
 51[scriptable, uuid(74567534-eb94-4b1c-8f45-389643bfc555)]
 52interface nsIPrefBranch2 : nsIPrefBranch
 53{
 54  /**
 55   * Add a preference change observer. On preference changes, the following
 56   * arguments will be passed to the nsIObserver.observe() method:
 57   *   aSubject - The nsIPrefBranch object (this)
 58   *   aTopic   - The string defined by NS_PREFBRANCH_PREFCHANGE_TOPIC_ID
 59   *   aData    - The name of the preference which has changed, relative to
 60   *              the |root| of the aSubject branch.
 61   *
 62   * aSubject.get*Pref(aData) will get the new value of the modified
 63   * preference. For example, if your observer is registered with
 64   * addObserver("bar.", ...) on a branch with root "foo.", modifying
 65   * the preference "foo.bar.baz" will trigger the observer, and aData
 66   * parameter will be "bar.baz".
 67   *
 68   * @param aDomain   The preference on which to listen for changes. This can
 69   *                  be the name of an entire branch to observe.
 70   *                  e.g. Holding the "root" prefbranch and calling
 71   *                  addObserver("foo.bar.", ...) will observe changes to
 72   *                  foo.bar.baz and foo.bar.bzip
 73   * @param aObserver The object to be notified if the preference changes.
 74   * @param aHoldWeak true  Hold a weak reference to |aObserver|. The object
 75   *                        must implement the nsISupportsWeakReference
 76   *                        interface or this will fail.
 77   *                  false Hold a strong reference to |aObserver|.
 78   *
 79   * @note
 80   * Registering as a preference observer can open an object to potential
 81   * cyclical references which will cause memory leaks. These cycles generally
 82   * occur because an object both registers itself as an observer (causing the
 83   * branch to hold a reference to the observer) and holds a reference to the
 84   * branch object for the purpose of getting/setting preference values. There
 85   * are 3 approaches which have been implemented in an attempt to avoid these
 86   * situations.
 87   * 1) The nsPrefBranch object supports nsISupportsWeakReference. Any consumer
 88   *    may hold a weak reference to it instead of a strong one.
 89   * 2) The nsPrefBranch object listens for xpcom-shutdown and frees all of the
 90   *    objects currently in its observer list. This ensures that long lived
 91   *    objects (services for example) will be freed correctly.
 92   * 3) The observer can request to be held as a weak reference when it is
 93   *    registered. This insures that shorter lived objects (say one tied to an
 94   *    open window) will not fall into the cyclical reference trap.
 95   *
 96   * @note
 97   * The list of registered observers may be changed during the dispatch of
 98   * nsPref:changed notification. However, the observers are not guaranteed
 99   * to be notified in any particular order, so you can't be sure whether the
100   * added/removed observer will be called during the notification when it
101   * is added/removed.
102   *
103   * @note
104   * It is possible to change preferences during the notification.
105   *
106   * @note
107   * It is not safe to change observers during this callback in Gecko 
108   * releases before 1.9. If you want a safe way to remove a pref observer,
109   * please use an nsITimer.
110   *
111   * @see nsIObserver
112   * @see removeObserver
113   */
114  void addObserver(in string aDomain, in nsIObserver aObserver,
115                   in boolean aHoldWeak);
116
117  /**
118   * Remove a preference change observer.
119   *
120   * @param aDomain   The preference which is being observed for changes.
121   * @param aObserver An observer previously registered with addObserver().
122   *
123   * @note
124   * Note that you must call removeObserver() on the same nsIPrefBranch2
125   * instance on which you called addObserver() in order to remove aObserver;
126   * otherwise, the observer will not be removed.
127   *
128   * @see nsIObserver
129   * @see addObserver
130   */
131  void removeObserver(in string aDomain, in nsIObserver aObserver);
132};
133
134%{C++
135
136/**
137 * Notification sent when a preference changes.
138 */
139#define NS_PREFBRANCH_PREFCHANGE_TOPIC_ID "nsPref:changed"
140
141%}