Thanks, that (along with the other comments here) was enough to get me started. I managed to get a basic proof-of-concept up and running. Oddly enough, I hadn't thought to check the Help browser until I saw the Announcements-Help package. Once I read it, I found it very helpful, so if anyone else comes looking for pointers, that's a good place to direct them. Regards, Johann On Fri, Aug 17, 2012 at 1:32 PM, Stéphane Ducasse <stephane.ducasse@inria.fr> wrote:
On Aug 17, 2012, at 3:46 PM, Johann Hibschman wrote:
I'm still relatively new to Pharo and to Smalltalk in general,
welcome :)
and I've hit a situation where I'd like a model that notifies dependent views when it changes.
Classically, it looks like this was done through #addDependent:, #update, #changed, #release and friends. I don't need more than a symbol message and an associated object, so I could live with that API, but I don't quite understand #release.
Do not use changed:/update because - it broadcasts to all the dependents - you have to build case statement in the update
It sounds like originally Object class held (non-weak) references to all objects that had dependents, so unless the dependents were explicitly released, the objects would never be released. I get the impression that at some point this was switched to using weak references, so I wouldn't have to worry about closed parent/dependent loops, but I can't find this explicitly spelled out anywhere.
- Question 1: Does the basic addDependent/etc. system on Pharo use weak references?
You can use on:send:to: on Morph or when: anEventSelector send: aMessaageSelector to: anObject on object You can also use Announcement.
- Question 2: Am I correct in understanding that the main point of the Model class was to avoid having an entry in the Object class variable, so a closed parent/dependent loop could be garbage collected?
This table in the Object is an old idea and we should remove it. People should use ValueHolder
- Question 3: If Pharo uses weak references, is there any point to the Model class?
I've also seen some references to the Announcements framework, but I can't find as much documentation on it as I can on the "basic" Smalltalk dependency mechanism. It seems a bit more complex, with actual event classes, but I've not understood it yet.
In fact you get an object and not only a symbol so you can pass more logic
- Question 4: Should I prefer using Announcements for even mostly trivial cases? when: anEventSelector send: aMessaageSelector to: anObject
which is should unify with the on:send:to: of Morph
- Question 5: What benefits would Announcements give me?
that you can pass a complex object around. Read the blog of Vassili on Announcement.
Any overall pointers would be appreciated as well.
Thanks, Johann