implementing sorting with QSortFilterProxyModel

[mzimmers]

@Christian-Ehrlicher ahh...and, since (according to the docs) QAbstractItemModel::sort() does nothing by default, I guess I do have to implement my own sort algorithm?

[Christian Ehrlicher]

@mzimmers said in implementing sorting with QSortFilterProxyModel:

I guess I do have to implement my own sort algorithm?

As already written you have to reimplement QSFPM::lessThan() if you want a custom sorting of your data.

[mzimmers]

@Christian-Ehrlicher I realize that. What I'm trying to understand is whether I need to re-implement sort() as well.

From the docs:
Sorts the model by column in the given order.
The base class implementation does nothing.

The Qt-supplied examples don't seem to directly invoke a sort() function, and the docs say that it's called behind the scenes. So, I'm still not sure what all I need to supply in order to effect a sort. I do have my lessThan() function defined and I'll flesh it out once I figure out how it gets invoked.

[Christian Ehrlicher]

@mzimmers said in implementing sorting with QSortFilterProxyModel:

What I'm trying to understand is whether I need to re-implement sort() as well.

If you don't want to use a QSortFilterProxyModel then yes.

[mzimmers]

@Christian-Ehrlicher we seem to be talking past each other...either that, or I'm especially dense this morning.

As stated in my first post, I do have a QSortFilterProxyModel set onto a QAbstractListModel. Here's the complete header:

class EquipmentValveProxy : public QSortFilterProxyModel
{
    Q_OBJECT
public:
    explicit EquipmentValveProxy(QObject *parent = nullptr);
protected:
    bool filterAcceptsRow(int sourceRow, const QModelIndex &sourceParent) const override;
    // void sort(int column, Qt::SortOrder = Qt::AscendingOrder) const;
    bool lessThan(const QModelIndex &left,
                  const QModelIndex &right) const override;
};

When I try to use QSortFilterProxyModel::sort(), I get this error:

equipmentValveProxy.cpp:22:5: 'this' argument to member function 'sort' has type 'const EquipmentValveProxy', but function is not marked const
qsortfilterproxymodel.h:157:10: 'sort' declared here

Am I supposed to implement my own sort() as a wrapper to QSortFilterProxyModel::sort()?

Thanks...

[Christian Ehrlicher]

@mzimmers said in implementing sorting with QSortFilterProxyModel:

Am I supposed to implement my own sort() as a wrapper to QSortFilterProxyModel::sort()?

Why?
Again: reimplement lessThan() and then sort your view. Nothing more.

[mzimmers]

@Christian-Ehrlicher

I have re-implemented lessThan(). It's currently a stub, but I'd expect it would still get called, if I can figure out how to invoke a sort.

But my attempts to use QSortFilterProxyModel::sort() produce a the above compile-time error.

[Christian Ehrlicher]

@mzimmers said in implementing sorting with QSortFilterProxyModel:

, if I can figure out how to invoke a sort.

already told you: It will be called as soon as you sort your view.

[mzimmers]

@Christian-Ehrlicher ahhhhhh...thank you for the emphasis; now I understand what you're saying. But...I don't know how to do that.

My view is a QML ListView. How does one effect a sort on that?

[Christian Ehrlicher]

I don't use QML but with QList/Table/TreeView the sorting is done by clicking on the header item.

You can call QSFPM::sort() from c++ but don't know how/if it is possible directly in the ListView

[JonB]

@mzimmers
I would just start by Googling QML QSortFilterProxyModel. https://stackoverflow.com/questions/45563393/sort-the-data-of-a-qml-listview-by-using-a-qsortfilterproxymodel might be just what you need to understand from QML (though it might be too detailed), I don't know. Note that it talks about implementing the lessThan(). That is all you have to do for a QSortFilterProxyModel. Its own code will call that repeatedly in order to present its source model in sorted order to the outside world.

[Ronel_qtmaster]

@mzimmers Here is an exemple.Hope it helps
SortOnSecondModel.h

class SortOnSecondModel : public QSortFilterProxyModel
{
public:
SortOnSecondModel( QObject *parent = 0 );
protected:
bool lessThan( const QModelIndex &left, const QModelIndex &right ) const;
};

SortOnSecondModel.cpp

bool SortOnSecondModel::lessThan( const QModelIndex &left,
const QModelIndex &right ) const
{
QString leftString = sourceModel()->data( left ).toString();
QString rightString = sourceModel()->data( right ).toString();
if( !leftString.isEmpty() )
leftString = leftString.mid( 1 );
if( !rightString.isEmpty() )
rightString = rightstring.mid( 1 );
return leftString < rightString;
}

[mzimmers]

@Ronel_qtmaster thanks for the example. I haven't gotten around to implementing my lessThan() function, because I'm still trying to figure out how/where to invoke the sort() call. This is what I'm trying:

EquipmentValveProxy::EquipmentValveProxy(EquipmentModel *equipmentModel, QObject *parent)
    : QSortFilterProxyModel{parent}, m_equipmentModel(equipmentModel)
{
    QObject::connect(m_equipmentModel, &EquipmentModel::modelUpdated, this, &EquipmentValveProxy::updateSorting);
}

void EquipmentValveProxy::updateSorting()
{
    invalidate();
    sort(0); // what should I use for a column?
}

This is successful in that it gets me into my lessThan() function, currently stubbed as:

bool EquipmentValveProxy::lessThan(const QModelIndex &left, const QModelIndex &right) const
{
    bool rc = false;

    QVariant leftData = sourceModel()->data(left);
    QVariant rightData = sourceModel()->data(right);
    return rc;
}

Unfortunately, I'm still doing something wrong, because both leftData and rightData are invalid after assignments. How does this look to you?

Thanks...

[Ronel_qtmaster]

@mzimmers said in implementing sorting with QSortFilterProxyModel:

To invoque the sort , you just need to call QTableView::setSortingEnabled( true );

In your EquipmentValveProxy class, you don't need any connect in the constructor, you only need to reimplement lessThan function.

Now you need to pass the model containing your data to the sorter class.
EquipmentValveProxy ::setSourceModel( &model );

Then set the sorter class as model to your QTableView
QTableView::setModel(&your_sorter_class);

And finally enable sorting using QTableView::setSortingEnabled( true );

[mzimmers]

@Ronel_qtmaster said in implementing sorting with QSortFilterProxyModel:

To invoque the sort , you just need to call QTableView::setSortingEnabled( true );

But...it's a QML ListView, not a C++ TableView.

[Ronel_qtmaster]

@mzimmers Okay.Then you should consider porting your model to qml https://doc.qt.io/qt-6/qtquick-modelviewsdata-cppmodels.html

[mzimmers]

@Ronel_qtmaster said in implementing sorting with QSortFilterProxyModel:

you should consider porting your model to qml

I assume you mean making my model available to QML? I've done that. I've gone through (most of) the steps in the video from the link you provided.

If you mean actually convert my model to a QML ListModel, that's not an option. My model code is ~1000 lines of C++ and fairly intricate; it's not conducive to conversion to QML.

What I'm doing (with the connection) seems to be working. In the debugger, it's alarmingly slow, but when run normally, performance seems OK. Unless there's a serious flaw in this approach, I think it's what I have to do.

[JonB]

@mzimmers said in implementing sorting with QSortFilterProxyModel:

sort(0); // what should I use for a column?

Not sure what your question is here? Only you know which column you want to sort by. If you go back to that full example I referenced on SO you will see they do indeed use m_messageProxyModel.sort(0, Qt::AscendingOrder); so that's the right thing to do.

The QTableView widget has a setSortingEnabled(). If set that enables "sort arrows" on each column header so user can click to sort by any column. The view invokes the QSFPM::sort() method with corresponding column/direction. If that is what you want (end-user sorting) does your QML "grid" or "table" or whatever offer this? Otherwise have a look at the accepted solution in that SO thread:

Alternatively, and if you want to do the sorting and filtering from QML and not c++, you could use my SortFilterProxyModel like so

So that guy has written a complete QML interface to doing sort/filtering for you just like QSFPM for widgets! Don't look a gift horse in the mouth. (Don't actually know what you're supposed to do with one, because if you take it in you get invaded, so just looking at it in the mouth seems as safe as anything to me...) Either take the whole thing or look up how he does relevant bits? You did look at this when I first gave you the reference, didn't you? ;-)

Unfortunately, I'm still doing something wrong, because both leftData and rightData are invalid after assignments. How does this look to you?

What do you mean "invalid after assignments"? That should correctly pick up the QVariant values at the model indexes, whatever those value are.

[mzimmers]

@JonB said in implementing sorting with QSortFilterProxyModel:

If you go back to that full example I referenced on SO you will see they do indeed use m_messageProxyModel.sort(0, Qt::AscendingOrder); so that's the right thing to do.

Yeah, I figured out that wasn't the problem a little after I posted.

The reason that my leftData and rightData variables were invalid were simply that I hadn't furnished a role from my model. I changed the lines to this:

    QVariant leftData = sourceModel()->data(left, EquipmentModel::NameRole);
    QVariant rightData = sourceModel()->data(right, EquipmentModel::NameRole);

And now it works. Incredibly slow in the debugger, but otherwise fine.

And yes, I did look at @GrecKo 's solution that he referenced on SO. If my needs become more elaborate than they currently are, I'll reconsider that option.

[GrecKo]

@mzimmers If your model is to be consumed in QML, it most likely has a single column and multiple roles if it's meant to be consumed by a ListView (multiple columns shouldn't be a thing unless you are implementing a spreadsheet, change my mind).

call setDynamicSortFilter(true) and sort(0) once at the beginning and you should be good to go. Your lessThan function will be called when needed. Or use my project on GitHub like mentioned above. It hasn't been updated for a while but it is still relevant. Take a look at the available forks too, there might be improvements there.