Here's a question for you cells wizards out there (and Kenny in particular):
Say, I have a model M that depends on the structure of a family tree. One of M's slots is therefore depending on the root of the family tree: (c? root). However, I want M to know about changes in the family tree, like, say, when a child or grandchild is added. Apparently cells (at least the cells_2.0 branch required by cells-gtk) does not broadcast change messages to the parents of a node (which I guess is the right thing in 99% of the cases).
What's the best way to deal with that?
(i) Is there some mechanism for this purpose present in cells? Or (ii) Do I roll my own special case solution? Or (iii) Is it worthwhile to build some general purpose solution to this problem?
My approach towards (ii) (I haven't coded anything yet, waiting for you comments) would be something like building an observer tree each node of which observes one node in the family tree. Something like this: - Design a tiny tree observer model ("tto"?), suited to observing one family node (defmodel tty (family) (observed observed-kids reports-to))
- Every tto knows about the parent model (M from above) and does the right thing when it sees a change (say, call a closure) - If the observed nodes has kids, it instantiates tto kids of its own to match the kids of the observed tree (def-c-output observed ((self tto)) (make-tto :observed (c? new-value) :observed-kids (c? (kids new-value))) (setf (kids self) (mapcar (lambda (kid) (make-tto :observed (c? kid) :observed-kids (c? (kids kid)))) (kids new-value) ...) (def-c-output observed-kids ((self tto)) ...)
- Changing the root slot in M results in the instantiation of a tto for the root
I guess that would work ... but I feel there must be a more elegant solution. I'm eager to hear your suggestions.
Thanks, Peter
Background:
If you have seen my ton of mails on the cells-gtk-devel list, you know I'm doing some GUI work with cells-gtk at the moment. I ran into the following issue: cells-gtk can use a family tree as a natural representation of the contents of a tree-view. However, when I change the items in that family tree, cells-gtk currently has no way of updating the C data structure correspondingly.
The tree-model data type GTK uses internally is nasty to deal with, and therefore I really want to capsulate everything away. I have already figured out how to add/remove rows and children in the model, so I'd be ready to modify the C data type to reflect changes in the family tree. I'm just looking for the Right Way to do it.