QComboBox multi-column popup selection quirks [SOLVED]

[ChrisW67]

Hi All,

I have a quick question regarding the behaviour of QComboBox with a multi-column QTableView custom view.

I have the combo box set up like this:

TypeModel *model = new TypeModel(this);
 
        QComboBox *combo = new QComboBox(central);
        QTableView *view = new QTableView(this);
        view->setModel(model);
        view->resizeColumnsToContents();
        view->resizeRowsToContents();
        view->verticalHeader()->setVisible(false);
        view->setMinimumWidth(view->horizontalHeader()->length());
        view->setHorizontalScrollBarPolicy(Qt::ScrollBarAsNeeded);
        view->setSelectionMode(QAbstractItemView::SingleSelection);
        view->setSelectionBehavior(QAbstractItemView::SelectRows);
        view->setAutoScroll(false);
 
        combo->setModel(model);
        combo->setModelColumn(0);
        combo->setView(view);

TypeModel *model = new TypeModel(this);

        QComboBox *combo = new QComboBox(central);
        QTableView *view = new QTableView(this);
        view->setModel(model);
        view->resizeColumnsToContents();
        view->resizeRowsToContents();
        view->verticalHeader()->setVisible(false);
        view->setMinimumWidth(view->horizontalHeader()->length());
        view->setHorizontalScrollBarPolicy(Qt::ScrollBarAsNeeded);
        view->setSelectionMode(QAbstractItemView::SingleSelection);
        view->setSelectionBehavior(QAbstractItemView::SelectRows);
        view->setAutoScroll(false);

        combo->setModel(model);
        combo->setModelColumn(0);
        combo->setView(view);

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TypeModel is a simple table model returning code-meaning pairs. The flags() method looks like:

// column 0 is the code, column 1 is the meaning
Qt::ItemFlags TypeModel::flags(const QModelIndex &index) const
{
    Qt::ItemFlags theFlags = QAbstractItemModel::flags(index);
    if (index.isValid()) {
        theFlags &= ~Qt::ItemIsEditable;
        if (index.column() != 0)
            theFlags &= ~Qt::ItemIsSelectable;
    }
    return theFlags;
}

// column 0 is the code, column 1 is the meaning
Qt::ItemFlags TypeModel::flags(const QModelIndex &index) const
{
    Qt::ItemFlags theFlags = QAbstractItemModel::flags(index);
    if (index.isValid()) {
        theFlags &= ~Qt::ItemIsEditable;
        if (index.column() != 0)
            theFlags &= ~Qt::ItemIsSelectable;
    }
    return theFlags;
}

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If lines 7 and 8 are as above then the combo pop-up only allows clicking on items in the first column, and the resulting code is displayed in the combo box. If lines 7-8 are omitted then the user can click on either column of the popup but the text of the cell they clicked on, which may be a meaning, is put in the combo box. Setting the model column for the combo box does not change this. In either case the combo box current index is correct.

Is there a way to have the popup clickable anywhere but have the code placed in the combo box?

Regards,
Chris

Full code attached. I am using Qt 4.6.3 on Linux.

[saa7_go]

In MainWindow constructor you can add:

connect(combo, SIGNAL(currentIndexChanged(int)), combo, SLOT(setCurrentIndex(int)));

connect(combo, SIGNAL(currentIndexChanged(int)), combo, SLOT(setCurrentIndex(int)));

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[ChrisW67]

A touch incestuous but it works I was looking at writing a slot to manually do something similar but this is the short version. It still strikes me as odd that the combo box happily displays a value that is not from the model column the combo box is set to use.

Thanks.

[wysota]

Setting the model column for the combo box does not change this.

Hmm... that's a bit strange since every code path I can see that leads to updating the combo's text goes through this method:

QString QComboBox::itemText(int index) const
{
    Q_D(const QComboBox);
    QModelIndex mi = d->model->index(index, d->modelColumn, d->root);
    return d->itemText(mi);
}

QString QComboBox::itemText(int index) const
{
    Q_D(const QComboBox);
    QModelIndex mi = d->model->index(index, d->modelColumn, d->root);
    return d->itemText(mi);
}

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... which would suggest the column model should be respected.

---

Added after 12 minutes:

I'd say it's a bug in QComboBoxPrivate::setCurrentIndex.

It says:

void QComboBoxPrivate::setCurrentIndex(const QModelIndex &mi)
{
    Q_Q(QComboBox);
    bool indexChanged = (mi != currentIndex);
    if (indexChanged)
        currentIndex = QPersistentModelIndex(mi);
    if (lineEdit) {
        QString newText = q->itemText(currentIndex.row());
        if (lineEdit->text() != newText)
            lineEdit->setText(newText); 
        updateLineEditGeometry();
    }
    if (indexChanged) {
        q->update();   
        _q_emitCurrentIndexChanged(currentIndex);
    }
}

void QComboBoxPrivate::setCurrentIndex(const QModelIndex &mi)
{
    Q_Q(QComboBox);
    bool indexChanged = (mi != currentIndex);
    if (indexChanged)
        currentIndex = QPersistentModelIndex(mi);
    if (lineEdit) {
        QString newText = q->itemText(currentIndex.row());
        if (lineEdit->text() != newText)
            lineEdit->setText(newText); 
        updateLineEditGeometry();
    }
    if (indexChanged) {
        q->update();   
        _q_emitCurrentIndexChanged(currentIndex);
    }
}

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and should be:

void QComboBoxPrivate::setCurrentIndex(QModelIndex mi)
{
    Q_Q(QComboBox);
    mi = model->index(mi.row(), modelColumn, mi.parent());
    bool indexChanged = (mi != currentIndex);
    if (indexChanged)
        currentIndex = QPersistentModelIndex(mi);
    if (lineEdit) {
        QString newText = q->itemText(currentIndex.row());
        if (lineEdit->text() != newText)
            lineEdit->setText(newText); 
        updateLineEditGeometry();
    }
    if (indexChanged) {
        q->update();   
        _q_emitCurrentIndexChanged(currentIndex);
    }
}

void QComboBoxPrivate::setCurrentIndex(QModelIndex mi)
{
    Q_Q(QComboBox);
    mi = model->index(mi.row(), modelColumn, mi.parent());
    bool indexChanged = (mi != currentIndex);
    if (indexChanged)
        currentIndex = QPersistentModelIndex(mi);
    if (lineEdit) {
        QString newText = q->itemText(currentIndex.row());
        if (lineEdit->text() != newText)
            lineEdit->setText(newText); 
        updateLineEditGeometry();
    }
    if (indexChanged) {
        q->update();   
        _q_emitCurrentIndexChanged(currentIndex);
    }
}

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[ChrisW67]

Indeed, and someone has beaten us to it: http://bugreports.qt.nokia.com/browse/QTBUG-10491