Re: Model/view ideas for GtkListBox/GtkFlowBox

Shotwell uses a layered model approach for this problem.  There's a signalled SourceCollection which contains all the objects known to the application, i.e. every photo in the library.

Each page of the application (i.e. Events, Tags, Last Imported, etc.) has a signalled ViewCollection which subscribes to the SourceCollection's signals and populates itself with whatever objects it wants to show.  That is, the ViewCollection is where filtering, sorting, even aggregation of multiple SourceCollections (i.e. display photos alongside videos) occurs.

The UI layer subscribes to the ViewCollection's signals, populates the screen with widgets, and reacts to signals being fired to update itself.

I don't know this is the approach everyone should use, or even if it's appropriate here, but we've had great success with this inside of Shotwell.  At one point I thought about adapting and simplifying it into a library that built upon Gee (a signalled collections library) but never got that going.

I spoke about this with Lars Uebernickel at Montreal, and would be happy to discuss it further with anyone else interested as well.

-- Jim

On Thu, Oct 24, 2013 at 8:45 AM, Xavier Claessens <xclaesse gmail com> wrote:
I definitely second that. Empathy/Contacts can easily have between 1000 to 5000 rows and I've measured that widget creation (and destruction) in GtkListBoxRow is a real bottleneck. It's a bit hidden by folks having even worse performances, though (but it improved recently and I did not re-test). I've opened for this recently. Another thing I would like to suggest for the model is advanced filtering. I've implemented it on GtkListBox but it could be a model thing instead. Dunno. See On mer., 2013-10-23 at 11:57 +0200, Alexander Larsson wrote:
More and more gnome apps are migrating to GtkListBox rather than GtkTreeView for lists, and we now have GtkFlowBox that replaces GtkIconView. These are nice for smaller lists, but with larger lists they are a bit heavy. We may want to look at optimizing whatever is possible, but at some point it makes sense to have a model/view split that allows us to have large models without having each item in the model be instantiated as a widget, both for performance reasons and ease of use. I've been thinking of ways to do this, and had plans to implement this, but atm I'm busy working on a side project, so I don't have time for this atm. I thought I'd write up a braindump of my ideas so that maybe someone else can look at it, or at least it won't be losts. So, the general idea is that we have a model, and we create and update row widgets from the model based on some kind of template. The new GtkBuilder class templates is an excellent example of how this could work. We then create widgets as needed as they are scrolled into (or near) view. One obvious problem with this is that we don't know the height of the rows until we have widgets for them, so the listbox probably has to be changed to implement GtkScrollable and do scrolling based on row-nr and average height rather than exact offsets. The model itself is a set of GObjects, where the data in the model is stored as GObject properties. This is very flexible, in that we have names (no more column nr shit) for the data that is easy to map to properties (like GBinding, possibly with some transform function) in the row widget template, as well as to generic sorting/filtering functions. Property notification makes incremental updates possible. The GProperty work being done will make it very simple to create such model objects, and make property lookups very efficient. Then we need to add a GObjectSet interface that has signals for when objects are added and removed to the set, which would be used as the model itself, but also as a property type for recursive models (i.e. trees). View updates on a model like this can be pretty efficient. We connect to the added/removed signals on the set and keep track of the items (and per-view info like selection status) in the view in a sorted & filtered GSequence, then we connect to notify on all the model elements and whenever we get it we look up the GParamSpec to see how it affects the model (i.e. are we filtering/sorting/showing the changed property). If anything is affected we flag things in the view and request and update on the frame clock, so that we can minimally update the view structure and any visible widgets at most once per frame. I believe we should also have some sort property caches in the view objects. For instance any sort by string we should be monitoring changes to the corresponding property and keep a g_utf8_collate_key() or g_utf8_collate_key_for_filename() key up to date for fast comparisons. That should easily integrate with the update cycle above. We should also allow sorting based on object relationships. For instance, if we had a "GObject *parent" property that could be used to create a tree view if the view supported specifying that a child should be sorted directly after its parent. You can event do more complex structures like the twitter-style "expand in-reply-to/replies before/after a tweet". _______________________________________________ gtk-devel-list mailing list gtk-devel-list gnome org
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