[Dev] Problem with collection notifications

[John Anderson]

Phillip J. Eby wrote:

> At 09:13 PM 9/25/2005 -0700, Ted Leung wrote:
>
>> On Sep 24, 2005, at 3:07 PM, John Anderson wrote:
>>
>>> Yes in some cases we don't want any notifications. Consider this case:
>>> wxWidgets handles the click, updates the selection on the screen and
>>> tells us about the change. As a result we store the change in the
>>> selection. The selection is a change to data that causes a
>>> notification,
>>> which causes a new unnecessary update to the screen. So typically when
>>> the system updates the screen we only need to save the change. When
>>> the
>>> data changes as a result of something the system can't handle we want
>>> notifications so we can update the screen. There are many other
>>> similar
>>> examples like this that crop up in practice.
>>
>>
>> It sounds like things like the selection should not be subscribing to
>> notifications.
>> In general, I don't see a way to solve this problem without building
>> UI knowledge
>> into the notification mechanism.
>
>
> Well, you can disable notifications *during* notifications.  That's 
> the simplest way to avoid cascading.  In point-to-point subscription 
> systems (like peak.events), you can also use the trick of removing the 
> current callback from the subscriber list when calling it, so other 
> subscribers will see events generated by that callback, but the 
> callback itself cannot receive events that it generates itself.
>
I tried to disable notifications during notifications, however this only 
works with our synchronous notifications, not our asynchronous ones -- 
which is the problem I first raised.