nsIObserverService

xpcom/ds/nsIObserverService.idl Scriptable

This interface provides methods to add, remove, notify, and enumerate observers of various notifications.

Inherits from: nsISupports Last changed in Gecko 0.9.6

The XPCOM nsObserverService implements this interface to provide global notifications for a variety of subsystems.

Implemented by @mozilla.org/observer-service;1 as a service:

var observerService = Components.classes["@mozilla.org/observer-service;1"]
                      .getService(Components.interfaces.nsIObserverService);

Method overview

void addObserver ( in nsIObserver anObserver, in string aTopic, in boolean ownsWeak);

nsISimpleEnumerator enumerateObservers ( in string aTopic );

void notifyObservers ( in nsISupports aSubject, in string aTopic, in wstring someData );

void removeObserver ( in nsIObserver anObserver, in string aTopic );

Methods

addObserver()

Registers a given listener for a notifications regarding the specified topic. See nsIObserver for a JavaScript example.

void addObserver(
  in nsIObserver anObserver,
  in string aTopic,
  in boolean ownsWeak
);

Parameters

anObserver

The nsIInterface object which will receive notifications.

aTopic

The notification topic or subject.

ownsWeak

If set to false , the nsIObserverService will hold a strong reference to anObserver . If set to true and anObserver supports the nsIWeakReference interface, a weak reference will be held. Otherwise an error will be returned. (In most cases, you should use false .)

enumerateObservers()

Called to enumerate all observers registered for a particular topic.

nsISimpleEnumerator enumerateObservers(
  in string aTopic 
);

Parameters

aTopic

The notification topic or subject.

Return value

Returns an enumeration of all registered listeners. See nsISimpleEnumerator .

notifyObservers()

This method is called to notify all observers for a particular topic. See Example .

void notifyObservers(
  in nsISupports aSubject,
  in string aTopic,
  in wstring someData 
);

Parameters

aSubject

A notification specific interface pointer. This usually corresponds to the source of the notification, but could be defined differently depending on the notification topic and may even be null .

aTopic

The notification topic. This string-valued key uniquely identifies the notification. This parameter must not be null .

someData

A notification specific string value. The meaning of this parameter is dependent on the topic. It may be null .

removeObserver()

This method is called to unregister an observer for a particular topic.

void removeObserver(
  in nsIObserver anObserver,
  in string aTopic 
);

Parameters

anObserver

The nsIObserver instance to remove.

aTopic

The notification topic or subject. This string-valued key uniquely identifies the notification. This parameter must not be null .

Example

This notifies all nsIObserver s watching the "myTopicID" topic with an additional data parameter.

1 Components.classes[ "@mozilla.org/observer-service;1" ]
2 .getService(Components.interfaces.nsIObserverService)
3 .notifyObservers( null , "myTopicID" , "someAdditionalInformationPassedAs'Data'Parameter" );

See also

• nsObserverService
• Observer Notifications provides an overview of observers and a list of built-in notifications fired by Mozilla.
• Usage examples are provided in the nsIObserver documentation.