gecko/modules/libpref/public/nsIPrefBranch2.idl

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/* -*- Mode: IDL; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* ***** BEGIN LICENSE BLOCK *****
* Version: MPL 1.1/GPL 2.0/LGPL 2.1
*
* The contents of this file are subject to the Mozilla 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/MPL/
*
* 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 MPL, 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 MPL, the GPL or the LGPL.
*
* ***** END LICENSE BLOCK ***** */
#include "nsIPrefBranch.idl"
interface nsIObserver;
/**
* nsIPrefBranch2 allows clients to observe changes to pref values.
*
* @see nsIPrefBranch
*/
[scriptable, uuid(784de8e2-e72f-441a-ae74-9d5fdfe13be3)]
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 name of the preference which has changed, relative to
* the |root| of the aSubject branch.
*
* aSubject.get*Pref(aData) will get the new value of the modified
* preference. For example, if your observer is registered with
* addObserver("bar.", ...) on a branch with root "foo.", modifying
* the preference "foo.bar.baz" will trigger the observer, and aData
* parameter will be "bar.baz".
*
* @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 ensures 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.
*
* @note
* The list of registered observers may be changed during the dispatch of
* nsPref:changed notification. However, the observers are not guaranteed
* to be notified in any particular order, so you can't be sure whether the
* added/removed observer will be called during the notification when it
* is added/removed.
*
* @note
* It is possible to change preferences during the notification.
*
* @note
* It is not safe to change observers during this callback in Gecko
* releases before 1.9. If you want a safe way to remove a pref observer,
* please use an nsITimer.
*
* @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().
*
* @note
* Note that you must call removeObserver() on the same nsIPrefBranch2
* instance on which you called addObserver() in order to remove aObserver;
* otherwise, the observer will not be removed.
*
* @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"
%}