1.1 --- /dev/null Thu Jan 01 00:00:00 1970 +0000
1.2 +++ b/services/common/observers.js Wed Dec 31 06:09:35 2014 +0100
1.3 @@ -0,0 +1,154 @@
1.4 +/* This Source Code Form is subject to the terms of the Mozilla Public
1.5 + * License, v. 2.0. If a copy of the MPL was not distributed with this
1.6 + * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
1.7 +
1.8 +#ifndef MERGED_COMPARTMENT
1.9 +
1.10 +this.EXPORTED_SYMBOLS = ["Observers"];
1.11 +
1.12 +const Cc = Components.classes;
1.13 +const Ci = Components.interfaces;
1.14 +const Cr = Components.results;
1.15 +const Cu = Components.utils;
1.16 +
1.17 +#endif
1.18 +
1.19 +Cu.import("resource://gre/modules/XPCOMUtils.jsm");
1.20 +
1.21 +/**
1.22 + * A service for adding, removing and notifying observers of notifications.
1.23 + * Wraps the nsIObserverService interface.
1.24 + *
1.25 + * @version 0.2
1.26 + */
1.27 +this.Observers = {
1.28 + /**
1.29 + * Register the given callback as an observer of the given topic.
1.30 + *
1.31 + * @param topic {String}
1.32 + * the topic to observe
1.33 + *
1.34 + * @param callback {Object}
1.35 + * the callback; an Object that implements nsIObserver or a Function
1.36 + * that gets called when the notification occurs
1.37 + *
1.38 + * @param thisObject {Object} [optional]
1.39 + * the object to use as |this| when calling a Function callback
1.40 + *
1.41 + * @returns the observer
1.42 + */
1.43 + add: function(topic, callback, thisObject) {
1.44 + let observer = new Observer(topic, callback, thisObject);
1.45 + this._cache.push(observer);
1.46 + this._service.addObserver(observer, topic, true);
1.47 +
1.48 + return observer;
1.49 + },
1.50 +
1.51 + /**
1.52 + * Unregister the given callback as an observer of the given topic.
1.53 + *
1.54 + * @param topic {String}
1.55 + * the topic being observed
1.56 + *
1.57 + * @param callback {Object}
1.58 + * the callback doing the observing
1.59 + *
1.60 + * @param thisObject {Object} [optional]
1.61 + * the object being used as |this| when calling a Function callback
1.62 + */
1.63 + remove: function(topic, callback, thisObject) {
1.64 + // This seems fairly inefficient, but I'm not sure how much better
1.65 + // we can make it. We could index by topic, but we can't index by callback
1.66 + // or thisObject, as far as I know, since the keys to JavaScript hashes
1.67 + // (a.k.a. objects) can apparently only be primitive values.
1.68 + let [observer] = this._cache.filter(function(v) v.topic == topic &&
1.69 + v.callback == callback &&
1.70 + v.thisObject == thisObject);
1.71 + if (observer) {
1.72 + this._service.removeObserver(observer, topic);
1.73 + this._cache.splice(this._cache.indexOf(observer), 1);
1.74 + }
1.75 + },
1.76 +
1.77 + /**
1.78 + * Notify observers about something.
1.79 + *
1.80 + * @param topic {String}
1.81 + * the topic to notify observers about
1.82 + *
1.83 + * @param subject {Object} [optional]
1.84 + * some information about the topic; can be any JS object or primitive
1.85 + *
1.86 + * @param data {String} [optional] [deprecated]
1.87 + * some more information about the topic; deprecated as the subject
1.88 + * is sufficient to pass all needed information to the JS observers
1.89 + * that this module targets; if you have multiple values to pass to
1.90 + * the observer, wrap them in an object and pass them via the subject
1.91 + * parameter (i.e.: { foo: 1, bar: "some string", baz: myObject })
1.92 + */
1.93 + notify: function(topic, subject, data) {
1.94 + subject = (typeof subject == "undefined") ? null : new Subject(subject);
1.95 + data = (typeof data == "undefined") ? null : data;
1.96 + this._service.notifyObservers(subject, topic, data);
1.97 + },
1.98 +
1.99 + _service: Cc["@mozilla.org/observer-service;1"].
1.100 + getService(Ci.nsIObserverService),
1.101 +
1.102 + /**
1.103 + * A cache of observers that have been added.
1.104 + *
1.105 + * We use this to remove observers when a caller calls |remove|.
1.106 + *
1.107 + * XXX This might result in reference cycles, causing memory leaks,
1.108 + * if we hold a reference to an observer that holds a reference to us.
1.109 + * Could we fix that by making this an independent top-level object
1.110 + * rather than a property of this object?
1.111 + */
1.112 + _cache: []
1.113 +};
1.114 +
1.115 +
1.116 +function Observer(topic, callback, thisObject) {
1.117 + this.topic = topic;
1.118 + this.callback = callback;
1.119 + this.thisObject = thisObject;
1.120 +}
1.121 +
1.122 +Observer.prototype = {
1.123 + QueryInterface: XPCOMUtils.generateQI([Ci.nsIObserver, Ci.nsISupportsWeakReference]),
1.124 + observe: function(subject, topic, data) {
1.125 + // Extract the wrapped object for subjects that are one of our wrappers
1.126 + // around a JS object. This way we support both wrapped subjects created
1.127 + // using this module and those that are real XPCOM components.
1.128 + if (subject && typeof subject == "object" &&
1.129 + ("wrappedJSObject" in subject) &&
1.130 + ("observersModuleSubjectWrapper" in subject.wrappedJSObject))
1.131 + subject = subject.wrappedJSObject.object;
1.132 +
1.133 + if (typeof this.callback == "function") {
1.134 + if (this.thisObject)
1.135 + this.callback.call(this.thisObject, subject, data);
1.136 + else
1.137 + this.callback(subject, data);
1.138 + }
1.139 + else // typeof this.callback == "object" (nsIObserver)
1.140 + this.callback.observe(subject, topic, data);
1.141 + }
1.142 +}
1.143 +
1.144 +
1.145 +function Subject(object) {
1.146 + // Double-wrap the object and set a property identifying the wrappedJSObject
1.147 + // as one of our wrappers to distinguish between subjects that are one of our
1.148 + // wrappers (which we should unwrap when notifying our observers) and those
1.149 + // that are real JS XPCOM components (which we should pass through unaltered).
1.150 + this.wrappedJSObject = { observersModuleSubjectWrapper: true, object: object };
1.151 +}
1.152 +
1.153 +Subject.prototype = {
1.154 + QueryInterface: XPCOMUtils.generateQI([]),
1.155 + getHelperForLanguage: function() {},
1.156 + getInterfaces: function() {}
1.157 +};
