Custom sortable columns in QFileSystemModel

Jo Jo

@JonB
Thank you! Do I understand correctly that in QSortFilterProxyModel::lessThan we have no way to delegate the call to the QFileSystemModel comparison function and we have to implement it ourselves?

JonB

@Jo-Jo
That is my understanding, unless you find better by searching.
You might also take heed of https://forum.qt.io/post/569839, where the author states/claims:

In order to use QFileSystemModel, you can as well re-implement the "sort" function since the base implementation does nothing:

https://doc.qt.io/qt-5/qfilesystemmodel.html#sort

If you want to sort like the one in the right, I would recommend using the QSortFilterProxyModel as is. If you want something more customizable then re-implementing the QFileSystemModel would be a better option.

While you are looking at that thread, note that it appears Windows File Explorer has further "customized" rules for file name sorting, such as where the file names contains digits where @Christian-Ehrlicher refers to void QCollator::setNumericMode(bool on).

Jo Jo

@JonB Thank you! Now I am fixed this problem and full implementation currently looks like this (see below) and I would be glad to receive any feedback.

#include <QApplication>
#include <QTreeView>
#include <QHeaderView>
#include <QFileSystemModel>
#include <QSortFilterProxyModel>

class CustomSortFilterProxyModel : public QSortFilterProxyModel
{
public:
    explicit CustomSortFilterProxyModel(QObject *parent = nullptr) : QSortFilterProxyModel(parent) {}

protected:
    bool lessThan(const QModelIndex &left, const QModelIndex &right) const override
    {
        auto model = (QFileSystemModel*)sourceModel();
        bool isLeftDir = model->isDir(left);
        bool isRightDir = model->isDir(right);

        if ((isLeftDir && isRightDir) || (!isLeftDir && !isRightDir))
        {
            QString const leftName  = model->data(left,  Qt::DisplayRole).toString();
            QString const rightName = model->data(right, Qt::DisplayRole).toString();

            const int compare = QString::localeAwareCompare(leftName, rightName);
            if(compare != 0) {
                return compare < 0;
            }
        }
        else if (isLeftDir)
        {
            return true;
        }

        return false;
    }
};

class Model : public QFileSystemModel
{
public:

    int columnCount(const QModelIndex& parent = QModelIndex()) const override
    {
        int cc = QFileSystemModel::columnCount(parent);

        if (cc == 0)
        {
            return 0;
        }

        return cc + 1;
    }

    QVariant data(const QModelIndex& index,int role) const override
    {
        if(index.isValid() && index.column() == 4)
        {
            QModelIndex sibling = index.siblingAtColumn(3);

            switch(role)
            {
                case(Qt::DisplayRole):
                {
                    return fileInfo(sibling).birthTime();
                }
                default:
                {
                    // return same role as in fourth (Date Modified) column at the current row
                    return QFileSystemModel::data(sibling, role);
                }
            }
        }

        return QFileSystemModel::data(index, role);
    }

    QVariant headerData(int section, Qt::Orientation orientation, int role = Qt::DisplayRole) const override
    {
        if (role == Qt::DisplayRole && orientation == Qt::Horizontal)
        {
            if (section == 4)
            {
                return QStringLiteral("Date Created");
            }
        }

        return QFileSystemModel::headerData(section, orientation, role);
    }
};

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);

    Model *model = new Model;
    model->setRootPath(QDir::rootPath());

    CustomSortFilterProxyModel* proxyModel = new CustomSortFilterProxyModel;

    proxyModel->setSourceModel(model);
    proxyModel->setSortRole(Qt::DisplayRole);

    QTreeView *treeView = new QTreeView;
    treeView->setSortingEnabled(true);
    treeView->setModel(proxyModel);
    treeView->setRootIndex(model->index("C:\\Users\\Username\\Desktop\\BOOK"));
    treeView->setColumnWidth(0, 250);
    treeView->setWindowTitle("QFileSystemModel Example");
    treeView->resize(600, 400);
    treeView->show();

    treeView->header()->setSortIndicator(0, Qt::AscendingOrder);

    return app.exec();
}

JonB

@Jo-Jo
Well, I could rewrite your lessThan() to use fewer lines and smaller expressions, becaue I am like that :) But it's not a big deal.

You started out with a lessThan which had special code for data comparison in a column. Now you seem to have an implementation which does not look at column data type and just does string comparisons on everything. Is the sufficient? Do you need a more complex "merger" of various approaches depending on data type? Depends what you want.

Jo Jo

@JonB I'm thinking about how to correctly implement comparison taking into account types but have some problems. Currently my code looks like this but not workiing properly. Maybe you can suggest solution?

class CustomSortFilterProxyModel : public QSortFilterProxyModel
{
    QList<int> m_dtCols{3,4};
public:
    explicit CustomSortFilterProxyModel(QObject *parent = nullptr) : QSortFilterProxyModel(parent) {}

protected:
    bool lessThan(const QModelIndex &left, const QModelIndex &right) const override
    {
        auto model = (QFileSystemModel*)sourceModel();
        bool isLeftDir = model->isDir(left);
        bool isRightDir = model->isDir(right);

        if ((isLeftDir && isRightDir) || (!isLeftDir && !isRightDir))
        {
            auto leftName  = model->data(left,  Qt::DisplayRole);
            auto rightName = model->data(right, Qt::DisplayRole);
            const int compare = m_dtCols.contains(sortColumn()) ?
                leftName.toDateTime() < rightName.toDateTime() :
                QString::localeAwareCompare(leftName.toString(), rightName.toString());

            if(compare != 0) {
                return compare < 0;
            }
        }
        else if (isLeftDir)
        {
            return true;
        }

        return false;
    }
};

JonB

I'm not sure what "not workiing properly" means? What does not work right? Have you put a break or qDebug() statements here to see/verify what it is comparing and returning?

Jo Jo

@JonB Sorry, sorting by "Date Modified" and "Date Created" columns does not work properly (yes, i use qDebug() for tests)

UPDATE:
I think it should be implemented like this

class CustomSortFilterProxyModel : public QSortFilterProxyModel
{
    QList<int> m_dtCols{3,4};
public:
    explicit CustomSortFilterProxyModel(QObject *parent = nullptr) : QSortFilterProxyModel(parent) {}

protected:
    bool lessThan(const QModelIndex &left, const QModelIndex &right) const override
    {
        auto model = (QFileSystemModel*)sourceModel();
        bool isLeftDir = model->isDir(left);
        bool isRightDir = model->isDir(right);

        if ((isLeftDir && isRightDir) || (!isLeftDir && !isRightDir))
        {
            auto leftName  = model->data(left,  Qt::DisplayRole);
            auto rightName = model->data(right, Qt::DisplayRole);

            if (m_dtCols.contains(sortColumn()))
            {
                return (leftName.toDateTime() < rightName.toDateTime());
            }

            const int compare = QString::localeAwareCompare(leftName.toString(), rightName.toString());

            if(compare != 0) {
                return compare < 0;
            }
        }
        else if (isLeftDir)
        {
            return true;
        }

        return false;
    }
};

But any improvement is appreciated

JonB

@Jo-Jo
Well, start by checking that goes through the toDateTime() path, what their values are and that is getting it right. I don't know what is wrong just by looking at it.

Btw, check whether the QString::localeAwareCompare(0 is case insensitive or case sensitive? Windows, but not Linux, sorts case insensitively, yours might not.

You have just updated your code: I'm not sure it is any different from what you first wrote, but if it is and works that's fine.

Jo Jo

@JonB Everything worked except for the "Date Modified" column. It turned out that Qt returns this date as a QString. I had to convert this string to QDateTime. Now the code looks like this:

class CustomSortFilterProxyModel : public QSortFilterProxyModel
{
    QList<int> m_dtCols{3,4};
public:
    explicit CustomSortFilterProxyModel(QObject *parent = nullptr) : QSortFilterProxyModel(parent) {}

protected:
    bool lessThan(const QModelIndex &left, const QModelIndex &right) const override
    {
        auto model = (QFileSystemModel*)sourceModel();
        bool isLeftDir = model->isDir(left);
        bool isRightDir = model->isDir(right);

        if ((isLeftDir && isRightDir) || (!isLeftDir && !isRightDir))
        {
            auto leftName  = model->data(left,  Qt::DisplayRole);
            auto rightName = model->data(right, Qt::DisplayRole);

            //return (leftName.toDateTime() < rightName.toDateTime()); // OK, works fine for dates

            if (m_dtCols.contains(sortColumn()))
            {
                if (sortColumn() == 3)
                {
                    QDateTime dt1 = QDateTime::fromString(leftName.toString(), "M/d/yyyy h:mm AP");
                    QDateTime dt2 = QDateTime::fromString(rightName.toString(), "M/d/yyyy h:mm AP");
                    return dt1 < dt2;
                }

                return (leftName.toDateTime() < rightName.toDateTime());
            }

            const int compare = QString::localeAwareCompare(leftName.toString(), rightName.toString());

            if(compare != 0) {
                return compare < 0;
            }
        }
        else if (isLeftDir)
        {
            return true;
        }

        return false;
    }
};

However, I'm not sure that I'm setting the date format correctly. It can change depending on the OS settings, or am I wrong?

Christian Ehrlicher

@Jo-Jo said in Custom sortable columns in QFileSystemModel:

I had to convert this string to QDateTime

You already converted the QVariant to a QDateTime above - so why do you use the way through QString now again?

Jo Jo

@Christian-Ehrlicher said in Custom sortable columns in QFileSystemModel:

You already converted the QVariant to a QDateTime above - so why do you use the way through QString now again?

Because "Date Modified" column is created by Qt and Qt using QString for this column. If I convert QVariant to QDateTime, in this case comparison does not work properly

Christian Ehrlicher

Then you should debug why ... e.g. with a qDebug() statement as @JonB already wrote some time ago....

JonB

@Jo-Jo said in Custom sortable columns in QFileSystemModel:

Everything worked except for the "Date Modified" column. It turned out that Qt returns this date as a QString.

I am surprised at this, but untested. You are now talking about a "Date Modified" column inbuilt into QFileSystemModel, and not the "creation date" column you added for your birthTime()? But that is QDateTime QFileSystemModel::lastModified(). So I don't understand where you are getting any string for a datetime which you need to convert.

Jo Jo

@JonB said in Custom sortable columns in QFileSystemModel:

You are now talking about a "Date Modified" column inbuilt into QFileSystemModel, and not the "creation date" column you added for your birthTime()?

Yes. This column value is QString, not QDateTime. You may check sources: https://codebrowser.dev/qt5/qtbase/src/widgets/dialogs/qfilesystemmodel.cpp.html#808

Christian Ehrlicher

Thast's why https://doc.qt.io/qt-6/qfilesystemmodel.html#lastModified is there.

JonB

@Jo-Jo
I now see that, and see from https://codebrowser.dev/qt5/qtbase/src/widgets/dialogs/qfilesystemmodel.cpp.html#737 that it is called in the implementation of QFileSystemModel::data() for column #3, which is what I needed to know.

I also see it is formatted as a string with QLocale::ShortFormat. I don't know what that looks like, I don't know how "precise" it is (e.g. down to, say, milliseconds or likely not?), I don't know what the locale-aware formatting does with it. Putting all these together it would not surprise me if it is unsuitable for sorting, and/or for converting back (accurately) to a datetime/comparing. Whereas the birthTime() you use for your extra column is indeed a datetime type and is suitable.

Hence, as both I and @Christian-Ehrlicher have said, I would use lastModified() just as you use birthDate() for this column in your own code for data() method.

Jo Jo

@Christian-Ehrlicher @JonB agree with you guys about lastModified, thanks!