[Interest] Why are selections not preserved in QListView when resorting?

[André Somers]

Scott Aron Bloom schreef op 12-11-2013 16:36:
>
> The reason its not there... is spelled QML...
>
Nonsense. It is not like selection policies got much love in QML either.

André

>
>
> *From:*interest-bounces+scott.bloom=onshorecs.com at qt-project.org 
> [mailto:interest-bounces+scott.bloom=onshorecs.com at qt-project.org] *On 
> Behalf Of *Philipp Kursawe
> *Sent:* Tuesday, November 12, 2013 7:09 AM
> *To:* interest at qt-project.org
> *Subject:* Re: [Interest] Why are selections not preserved in 
> QListView when resorting?
>
> I imagine, as often, its not a lot of code, but I wonder why this 
> basic, expected behaviour is not in all the selectable views in the 
> first place?
>
> I like to use PersistentIndex a lot in my background data update code, 
> so I will try to come up with a solution here. I will post the code later.
>
> On Tue, Nov 12, 2013 at 3:08 PM, Bo Thorsen <bthorsen at ics.com 
> <mailto:bthorsen at ics.com>> wrote:
>
>     If you need to do this, it's actually not hard to do.
>
>     Catch the sort just before it happens. Grab the current selection. Map
>     the indexes to the source model. Sort. Remap the indexes to the new
>     selection. Apply to the view.
>
>     It might look at bit complicated in text, but the code is
>     straightforward and easy to do.
>
>     You can probably make it even simpler by using a persistent index.
>
>     It's been years since I last did this, so I can't give you more
>     details.
>     But I remember that it wasn't hard to do.
>
>     Bo.
>
>     Den 12-11-2013 14:16, Philipp Kursawe skrev:
>
>     > Thanks André. It's things like this that make me wonder if we have
>     > chosen the right framework from time to time. Given that the Win32
>     > ListView has all this functionality and much more what Qt has to
>     offer.
>     > But then Win32 API has no concept of signals/slots like this,
>     but one
>     > could certainly mimic it using the Windows message loop.
>     >
>     >
>     > On Tue, Nov 12, 2013 at 2:00 PM, André Somers
>     <andre at familiesomers.nl <mailto:andre at familiesomers.nl>
>
>     > <mailto:andre at familiesomers.nl <mailto:andre at familiesomers.nl>>>
>     wrote:
>     >
>     >     Philipp Kursawe schreef op 12-11-2013 13:46:
>     >      > There seems to be no concept of selection preservation in
>     QListView
>     >      > (an probably other QAIViews).
>     >      > When I select the second element and then re-order the
>     list, the
>     >      > selected item is still the second (index) but models data
>     on index 2
>     >      > is not the same anymore.
>     >      >
>     >      > Am I doing something wrong?
>     >     No, I don´t think you´re doing anything wrong. QSFPM is.
>     >     The problem is that resorting isn´t using the
>     beginMoveRows/endMoveRows
>     >     methods. The QItemSelectionModel has no way to know that the
>     items in
>     >     the model have moved. It has no concept of there being an
>     underlying
>     >     model that your _really_ looking at. By using the move
>     signals, QSFPM
>     >     could in principal signal that items have not changed or the
>     model
>     >     reset, but items merely have moved, and QISM could use that
>     signal to
>     >     update itself, but again: it is unfortunately currently not
>     implemented
>     >     that way.
>     >
>     >     André
>     >
>     >
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>
>     --
>     Bo Thorsen, European Engineering Manager, ICS
>     Integrated Computer Solutions. Delivering World-Class Applications
>     http://ics.com/services
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