Using observers
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An extension overlaying the Firefox browser window will have one "instance" for each window, that is completely separate from all other windows—you cannot share variables. There are several ways to implement cross-window communication—probably the most convenient one is using observers (see also XulPlanet article).
There are two interfaces in the Mozilla platform related to observers system: nsIObserverService
which is available as a service, and nsIObserver
, which is what you'll need to implement.
Observer object
Each observer implements nsIObserver
interface. It may register for one or more topics. For each notification, its observe
function is called with the subject (can be null), the topic and additional data. All three parameters can be freely used by the code invoking the notification, see "Notify all observers" below.
In the snippet below we also include register
and unregister
convenience functions, which are not a part of nsIObserver interface. Including these functions in the observer object is a matter of taste.
function myObserver() { this.register(); } myObserver.prototype = { observe: function(subject, topic, data) { // Do your stuff here. }, register: function() { var observerService = Components.classes["@mozilla.org/observer-service;1"] .getService(Components.interfaces.nsIObserverService); observerService.addObserver(this, "myTopicID", false); }, unregister: function() { var observerService = Components.classes["@mozilla.org/observer-service;1"] .getService(Components.interfaces.nsIObserverService); observerService.removeObserver(this, "myTopicID"); } }
Instantiate and register
Do the following in your init function (probably an onload handler) for each window:
var observer = new myObserver();
Note: myObserver
's register
method is called once in the constructor, so no need to call it manually.
You must also unregister your observer when the window is closed (probably in an onunload
handler or earlier). Failing to do so will leak the window and cause various errors.
Notify all observers
You can send a notifications to all observers using nsIObserverService.notifyObservers()
:
Components.classes["@mozilla.org/observer-service;1"] .getService(Components.interfaces.nsIObserverService) .notifyObservers(null, "myTopicID", "someAdditionalInformationPassedAs'Data'Parameter");