the Observers module for simpler registration of observers that observe notifications

Observers.js

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+/* ***** 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 Observers.
+ *
+ * The Initial Developer of the Original Code is Daniel Aquino.
+ * Portions created by the Initial Developer are Copyright (C) 2008
+ * the Initial Developer. All Rights Reserved.
+ *
+ * Contributor(s):
+ *   Daniel Aquino <mr.danielaquino@gmail.com>
+ *   Myk Melez <myk@mozilla.org>
+ *
+ * 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 ***** */
+
+let EXPORTED_SYMBOLS = ["Observers"];
+
+const Cc = Components.classes;
+const Ci = Components.interfaces;
+const Cr = Components.results;
+const Cu = Components.utils;
+
+Cu.import("resource://gre/modules/XPCOMUtils.jsm");
+
+let Observers = {
+  add: function(callback, topic) {
+    let observer = new Observer(callback);
+    if (!(topic in Observers._observers))
+      Observers._observers[topic] = {};
+    Observers._observers[topic][callback] = observer;
+    Observers._service.addObserver(observer, topic, true);
+    return observer;
+  },
+
+  remove: function(callback, topic) {
+    let observer = Observers._observers[topic][callback];
+    if (observer) {
+      Observers._service.removeObserver(observer, topic);
+      delete this._observers[topic][callback];
+    }
+  },
+
+  notify: function(subject, topic, data) {
+    Observers._service.notifyObservers(new Subject(subject), topic, data);
+  },
+
+  _service: Cc["@mozilla.org/observer-service;1"].
+            getService(Ci.nsIObserverService),
+
+  // Observers indexed by callback.  This lets us get the observer
+  // to remove when a caller calls |remove|, passing it a callback.
+  _observers: {}
+};
+
+
+function Observer(callback) {
+  this._callback = callback;
+}
+
+Observer.prototype = {
+  QueryInterface: XPCOMUtils.generateQI([Ci.nsIObserver, Ci.nsISupportsWeakReference]),
+  observe: function(subject, topic, data) {
+    // Pass the wrappedJSObject for subjects that have one.  Otherwise pass
+    // the subject itself.  This way we support both wrapped subjects created
+    // using this module and those that are real XPCOM components.
+    let unwrappedSubject = subject.wrappedJSObject || subject;
+
+    if (typeof this._callback == "function")
+      this._callback(unwrappedSubject, topic, data);
+    else
+      this._callback.observe(unwrappedSubject, topic, data);
+  }
+}
+
+
+function Subject(object) {
+  this.wrappedJSObject = object;
+}
+
+Subject.prototype = {
+  QueryInterface: XPCOMUtils.generateQI([]),
+  getHelperForLanguage: function() {},
+  getInterfaces: function() {}
+};