On Thursday, October 04, 2012 16:38:42 Jan Kundrát wrote: > Hi, > my application makes heavy use of QAIM::reset() in its proxy models, > most notably in situations where the parent model either "goes away" or > otherwise fails in a manner which cannot be accommodated by the > beginResetModel/endResetModel pair of functions. I could convert some of > these into proper pairs, but others (like the parent model being > destroyed) have no choice but to signal the "sorry, everything is gone" > situation and carry on.
Yes, that's a tricky situation. I looked into it a few years ago, but I don't recall what I concluded about what should be done. > I have always assumed that the users of the model are more or less free > to call a "reasonable" subset of model's functions form inside slots > attached to modelAboutToBeReset() -- like index(), parent() and data(). Yes, you should be able to call any const method on a model which just emitted modelAboutToBeReset. > My models are probably buggy in this regard (they use lazy loading which > means that they should probably explicitly check for a reset being in > progress and disable any dynamic updates from this context -- some of > them do, others don't). This sounds fishy. You must not return to the event loop between beginResetModel and endResetModel. > I've always used reset() in my code to indicate > that this is a place where the code is doing either something > suspicious, or where it does not have any other way but emit this signal. > > I have also believed that calling reset() is "safe" in that it is > somehow different than emitting modelAboutToBeReset/modelReset. It's not different. > In Qt4, > the implementation of QAIM::reset() is in the .cpp file which I haven't > seen until now. It just emits these signals and invalidates the > persistent indexes. In Qt5, it's different It's the same. The Qt 5 code calls QAIM::endResetModel, which invalidates the persistent indexes. > -- the code actually does > nothing but calling the beginResetModel()/endResetModel() pair, so it is > as "safe" as doing that by hand. > > What shall my Qt5 code do when a proxy model discovers that the source > model is no longer there? Some of my proxies build internal data > structures which contain pointers to data in the source model; at the > time the source model gets missing, I really shouldn't be accessing > these anymore. Indeed. If you clear those and call endResetModel, it might work. It depends on whether any code depends on modelAboutToBeReset being emitted first, which I don't remember. Thanks, -- Stephen Kelly <stephen.ke...@kdab.com> | Software Engineer KDAB (Deutschland) GmbH & Co.KG, a KDAB Group Company www.kdab.com || Germany +49-30-521325470 || Sweden (HQ) +46-563-540090 KDAB - Qt Experts - Platform-Independent Software Solutions ** Qt Developer Conference: http://qtconference.kdab.com/ **
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