[Dev] Problem with collection notifications
john at osafoundation.org
Sat Sep 24 15:07:20 PDT 2005
Phillip J. Eby wrote:
> At 02:03 PM 9/24/2005 -0700, John Anderson wrote:
>> UI state is persisted in the block. After all, in the MVC paradigm
>> for UI, the block is the model and the widget is the view. When the
>> widget tells us of a change like the position or state of a window,
>> we need to store it in the block and typically the UI is already up
>> to date so there is no need for a notication.
> In which case, the update should be convergent, right? I mean, you'd
> be setting it to the same value that's already there, so there
> shouldn't be any further notifications after the first one, or else
> I'd say the notification system is generating spurious notifications.
> Or are you saying the problem is that you don't want even *one*
> notification in this case?
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.
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