[Dev] Problem with collection notifications

[Phillip J. Eby]

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.