308798 - [RFE] Need standard way to add and remove event listeners to XPCOM objects

Status: RESOLVED WONTFIX

(Core :: XPCOM, enhancement)

Description

[bastiaan]

User-Agent:       Mozilla/5.0 (Windows; U; Windows NT 5.0; en-US; rv:1.7.10) Gecko/20050716 Firefox/1.0.6
Build Identifier: Mozilla/5.0 (Windows; U; Windows NT 5.0; en-US; rv:1.7.10) Gecko/20050716 Firefox/1.0.6

The way XPCOM exposes events and allows listeners to consume these events is
different for almost every XPCOM object. There needs to be a coding convention
on how to make XPCOM objects that expose events and allow listeners/handlers to
be added and removed.
For instance, nsIMsgSend notifies a nsIMsgSendListener onStartSending and
onStopSending, etc., but there is no good way to add a nsIMsgSendListener to a
nsIMsgSend instance. The only way is to pass it as a parameter to the
nsIMsgSend.createAndSendMessage and sendMessageFile methods.

Other objects expose the listener as a property of the object. For instance,
nsIMsgCompose has a recyclingListener property.

Sometimes the listener can be added to or removed from an object with
addListener and removeListener, as is the case with nsISoapTransport.

This is the way I would prefer event listener to be added and removed.

I understand that refactoring all existing code is almost impossible as it would
break a lot of existing products and extensions, but it might be possible to add
the 'new-and-improved' way and leaving the old code intact (deprecating it for
future use).

This would be very useful to have, and would easify making extensions that want
to act upon XPCOM 'events'.

Reproducible: Always

Steps to Reproduce:

Comment 1

[Matthijs Wensveen]

Yes, I agree with you. Currently it is almost impossible to know what is going
on in XPCOM objects. Searching the documentation and code for ways to get
notified on certain events is really hard and frustrating, especially when you
finally discover that it is impossible to do what you're trying to do.

I think it is necessary to define what an event really is and how handlers
should be managed and notified.

I think we are talking about different types of events than nsIEventQueue stuff?

Comment 2

[bastiaan]

*** Bug 308807 has been marked as a duplicate of this bug. ***

Comment 3

[Doug Turner (:dougt)]

mass reassigning to nobody.

Comment 4

[Nickolay_Ponomarev]

Might be interesting to our excellent evangelism team. Ccing mfinkle and jresig.