[Qt-interest] ModelView - how to use proxies to filter this data?

Wed Dec 16 18:23:32 CET 2009

Daniel Price wrote:

> Thanks. That seems kinda complex to me though.
> 
> Let me know how it goes. An running example of your more generic solution
> when you implement it would be awesome!

Yeah. Complexity is an issue.

> 
> The biggest problem I've had is keeping everything in-sync; if I edit a
> branch of data via a proxy I want that change to propagate to all other
> proxies and views.

Yes. That's pretty much required.

> I've not been able to get this working 100%. It seems
> that with *some* proxies, you have to transmit the signals yourself. 

You probably have to re transmit all signals yourself for the proxy model 
where it is relevant to do so.

> For
> signals like dataChanged() this is easy, but for others like
> rowsInserted(), the signal is private to QAbstractItemModel so you can't
> emit it.

You have to use beginInsertRows/endInsertRows just like when implementing 
QAbstractItemModel.

> I've been using the code for the QSortFilterProxyModel as a guide
> b ut it's so complex it's hard to follow.
> 
> My solution so far has to been to abandon proxies and instead nest
> sub-model adaptors in the hierarchy (itself maintained by a single tree of
> data nodes with a conventional tree adaptor).
> 
> Each 'row' has two columns - an data type enumeration and a shared pointer
> to a table-model. The model contains a pointer to the relevant data
> structure. In my prototype I have a treeview with the major branch nodes -
> selecting these switches the data source of a single tableview to the
> relevant sub-model. This has the advantage that model-adaptors can be
> lazy-loaded and destroyed when not needed.

You mean you have multiple QAbstractTableModels (or so), and a selection in 
the tree brings a different table into the tableview?

Can I see the code?

Steve.

> 
> It works, for the most part, but it's a little convoluted. It might be
> easier to build my own custom graph-based MVC framework because the strict
> concept 'rows' and 'columns' isn't a good match for my graphical app.
> 
>> -----Original Message-----
>> From: Stephen Kelly [mailto:steveire at gmail.com]
>> Sent: 14 December 2009 11:17
>> To: Daniel Price; qt-interest at trolltech.com
>> Subject: Re: [Qt-interest] ModelView - how to use proxies to filter
>> this data?
>>
>> On Wed, Dec 2, 2009 at 2:18 PM, Daniel Price <daniel.price at fxhome.com>
>> wrote:
>> > Can I see the source code for DescendantEntitiesProxyModel? I'm not
>> familiar with KDE underpinnings.
>> >
>> > From my experimentation so far, proxy models can only remove items
>> from the model. They cannot change the fundamental structure so if the
>> source is a tree, they will still display a tree.
>>
>> Hey, sorry for the very late reply. The LGPL code is now here:
>>
>> http://websvn.kde.org/trunk/KDE/kdepimlibs/akonadi/kdescendantsproxymod
>> el_p.h?view=markup
>> http://websvn.kde.org/trunk/KDE/kdepimlibs/akonadi/kdescendantsproxymod
>> el.cpp?view=markup
>>
>> Note that it is also broken in a subtle way because it uses the
>> internalPointer() of source model indexes. My intention is to replace
>> it with the even more generic KReparentingProxyModel
>>
>> http://websvn.kde.org/trunk/KDE/kdepim/akonadi/akonadi_next/kreparentin
>> gproxymodel.h?view=markup
>>
>> It can turn a list into a tree (for email threading for example), a
>> tree into a list, or a tree into a different tree. So yes, you can
>> change the fundamental structure of the model, but it's not trivial if
>> you want to keep up to date with source model changes.
>>
>> All the best,
>>
>> Steve.
>>
>> >
>> >> -----Original Message-----
>> >> From: Stephen Kelly [mailto:steveire at gmail.com]
>> >> Sent: 02 December 2009 13:14
>> >> To: Daniel Price
>> >> Subject: Re: [Qt-interest] ModelView - how to use proxies to filter
>> >> this data?
>> >>
>> >> Daniel Price wrote:
>> >>
>> >> > I've been playing with this sortfilter approach and it works fine
>> if
>> >> the
>> >> > layout of the source matches the output. However, what if my
>> source
>> >> items
>> >> > are buried away?
>> >> >
>> >> > Eg:
>> >> >
>> >> > --Companies
>> >> > ----Company1
>> >> > ------Product1
>> >> > ------Product2
>> >> > ------Product3
>> >> > ----Company2
>> >> > ------Product4
>> >> >
>> >> > The above is stored within a QAbstractItemModel and I want to use
>> a
>> >> proxy
>> >> > to just pull out all the products to give me this in a table:
>> >> >
>> >> > --Product1
>> >> > --Product2
>> >> > --Product3
>> >> > --Product4
>> >> >
>> >> > How could I do this using a proxy? If I store a unique identifier
>> in
>> >> each
>> >> > of the product rows identifying it as a Product record, could I
>> >> somehow
>> >> > use the built-in filtering to get just those rows?
>> >>
>> >> You could do this using a proxy. The way I've done it is to flatten
>> the
>> >> tree
>> >> into a list, then filter out Company* from the list.
>> >>
>> >> Some screenshots here:
>> >>
>> >> http://api.kde.org/playground-api/pim-
>> >> apidocs/akonadi/akonadi_next/html/index.html
>> >>
>> >> (Look for DescendantEntitiesProxyModel)
>> >>
>> >> All the best,
>> >>
>> >> Steve.
>> >>
>> >> >
>> >> >
>> >> >> -----Original Message-----
>> >> >> From: qt-interest-bounces at trolltech.com [mailto:qt-interest-
>> >> >> bounces at trolltech.com] On Behalf Of Sean Harmer
>> >> >> Sent: 01 December 2009 15:54
>> >> >> To: qt-interest at trolltech.com
>> >> >> Subject: Re: [Qt-interest] ModelView - how to use proxies to
>> filter
>> >> >> this data?
>> >> >>
>> >> >> Hi,
>> >> >>
>> >> >> On Tuesday 01 December 2009 15:36:18 Daniel Price wrote:
>> >> >> > Thanks for the info. I hadn't considered using a proxy filter
>> and
>> >> >> just
>> >> >> >  accepting/rejecting rows. Does that work with hierarchical
>> data
>> >> >> though?
>> >> >>
>> >> >> Yes it works absolutely fine with hierarchical data as that is
>> what
>> >> I
>> >> >> am using.
>> >> >>
>> >> >> > I actually QAbstractProxyModel and implemented the
>> mapTo/mapFrom
>> >> >> functions.
>> >> >> >  But sorting doesn't seem to work.
>> >> >>
>> >> >> Yeah I thought about doing it that way, but then decided that
>> >> >> QSortFilterProxyModel fitted my needs with a little subclassing.
>> >> >>
>> >> >> > BTW it looks like you're storing pointers to your structures in
>> >> your
>> >> >> >  variants as integers and casting them back.
>> >> >>
>> >> >> No I am storing them as void* in the QModelIndex's internal
>> pointer
>> >> so
>> >> >> that is
>> >> >> why I am casting them back to my specific types. My model's index
>> >> >> function
>> >> >> looks like this:
>> >> >>
>> >> >> QModelIndex MapsData1DTreeModel::index( int row, int col, const
>> >> >> QModelIndex&
>> >> >> parent ) const
>> >> >> {
>> >> >>     MapsData1DTreeModelGroupNode* parentItem;
>> >> >>     if ( !parent.isValid() )
>> >> >>         parentItem = m_root;
>> >> >>     else
>> >> >>         parentItem = static_cast<MapsData1DTreeModelGroupNode*>(
>> >> >> parent.internalPointer() );
>> >> >>
>> >> >>     MapsData1DTreeModelNode* childItem = parentItem->child( row
>> );
>> >> >>     if ( childItem )
>> >> >>         return createIndex( row, col, childItem );
>> >> >>     else
>> >> >>         return QModelIndex();
>> >> >> }
>> >> >>
>> >> >> Good luck.
>> >> >>
>> >> >> Sean
>> >> >> _______________________________________________
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>> >> >> Qt-interest at trolltech.com
>> >> >> http://lists.trolltech.com/mailman/listinfo/qt-interest
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