[Interest] Why doesn't my model filter update?

Florian Bruhin me at the-compiler.org
Wed Feb 19 13:54:43 CET 2020


On Tue, Feb 18, 2020 at 04:49:57PM -0500, Matthew Woehlke wrote:
> On 18/02/2020 16.31, Konstantin Shegunov wrote:
> > On Tue, Feb 18, 2020 at 11:20 PM Matthew Woehlke wrote:
> >> I wonder if anyone else can spot it? ;-)
> > 
> > Without knowing anything about the code at all, my best guess based on a
> > very quick glance would be the range for the dataChanged is wrong.
> 
> Okay, I'll give you half a cookie, since I can't really say much more
> without giving it away. (Incidentally, if I hadn't already figured it
> out, you comment probably would have helped!)
> 
> Here's the broken code:
> 
>   if (auto const rows = this->rowCount())
>   {
>     auto const& first = this->index(0, 0);
>     auto const& last = this->index(rows, 0);
> 
>     emit this->dataChanged(first, last, {MyFilterRole});
>   }
> 
> It fell victim to one of the two hard problems of programming (as
> enumerated by Leon Bambrick┬╣). To wit, `last` is an invalid index, which
> trips one of the sanity checks in QSortFilterProxyModel's internal logic.
> 
> If you can't tell *why* `last` is invalid, well, keep looking until you
> can ;-). All the information you need to spot the problem is in the
> above snippet, and it's *obvious* once you see it. (Note: assume that
> the class otherwise behaves in a correct fashion.)
> 
> (┬╣ https://www.goodreads.com/quotes/7443069)

I'd recommend running QAbstractItemModelTester (or ideally, including it in
your testsuite) over custom models:

https://doc.qt.io/qt-5/qabstractitemmodeltester.html

It'd likely have caught an issue like this (though I haven't checked).

Florian

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