Problem with pressing TAB key during QTableView cell edit

[Ben35]

Hello all,

PROBLEM

I have a problem with the editing behaviour in a QTableView (i'm using Qt4.8). I have a QTableView in which i defined custom ItemDelegates with custom editors :

• a custom widget A which inherits from QComboBox;
• a custom widget B which inherits from QWidget and that contains a custom QDoubleSpinBox which inherits from QDoubleSpinBox;

When i start edit a cell, a TAB keypress validates the current edition an the next cell becomes editable, which is the standard behaviour of QTableView. But with my custom editor widget B, when i press TAB during the edition, the focus is given to the next cell, but not in an editing mode. I don't have this problem with my custom widget A. I guess it is because this widget is composed with an internal spinbox.

RESEARCH

When a view calls createEditor function of delegate it also installs the delegate event filter to editor, so i guess that events on editor widgets are trapped and treated by the ItemDelegate :

QWidget *QAbstractItemViewPrivate::editor(const QModelIndex &index,
                                          const QStyleOptionViewItem &options)
{
    Q_Q(QAbstractItemView);
    QWidget *w = editorForIndex(index).widget.data();
    if (!w) {
        QAbstractItemDelegate *delegate = delegateForIndex(index);
        if (!delegate)
            return 0;
        w = delegate->createEditor(viewport, options, index);
        if (w) {
           w->installEventFilter(delegate);
    ......
}

With the widget A, which work perfectly, the keyPressEvent is treated in eventFilter method of my delegate :

bool QStyledItemDelegate::eventFilter(QObject *object, QEvent *event)
{
    QWidget *editor = qobject_cast<QWidget*>(object);
    if (!editor)
        return false;
    if (event->type() == QEvent::KeyPress) {
        switch (static_cast<QKeyEvent *>(event)->key()) {
        case Qt::Key_Tab:
            emit commitData(editor);
            emit closeEditor(editor, QAbstractItemDelegate::EditNextItem);
            return true;
        case Qt::Key_Backtab:
            emit commitData(editor);
            emit closeEditor(editor, QAbstractItemDelegate::EditPreviousItem);

}

With my widget B, this eventFilter method doesn't receive the KeyPressEvent which is actually treated by the QWidget::event(QEvent *event) method of my internal spinbox, which explains why it does a focusNextPrevChild instead of the closeEditor(editor, QAbstractItemDelegate::EditNextItem) that i would expect.

    case QEvent::KeyPress: {
        QKeyEvent *k = (QKeyEvent *)event;
        bool res = false;
        if (!(k->modifiers() & (Qt::ControlModifier | Qt::AltModifier))) {  //### Add MetaModifier?
            if (k->key() == Qt::Key_Backtab
                || (k->key() == Qt::Key_Tab && (k->modifiers() & Qt::ShiftModifier)))
                res = focusNextPrevChild(false);
            else if (k->key() == Qt::Key_Tab)
                res = focusNextPrevChild(true);
            if (res)
                break;
        }

WHY ?

I don't undestand how to resolve my problem, and why this keyPressEvent on my custom editor B is not treated by the delegate.

In my custom editor widget B, i already did this :

setFocusPolicy(Qt::WheelFocus);
setFocusProxy(internalSpinbox);

Anyone to save me ? :)

[raven-worx]

@Ben35 said:

I don't undestand how to resolve my problem, and why this keyPressEvent on my custom editor B is not treated by the delegate.

Because the item delegate is only installed as event filter on the widget you create as editor. But you need to filter events of a child widget.
So when creating the editor widget you also need to make sure to install the item delegate (this) as event filter on the sub-editor-widget.

[Ben35]

Not sure how i can do this ...

[Ben35]

I think i've found a solution.

First, i install an eventFilter in my custom editor widget B on the internal spinbox :

internalSpinbox->installEventFilter(this);

Then, i implement eventFilter to treat the events on the spinbox and duplicate them to the parent:

bool AbstractRatioQuantitySpinbox::eventFilter(QObject *object, QEvent *event)
{
    // cf http://stackoverflow.com/questions/12145522/why-pressing-of-tab-key-emits-only-qeventshortcutoverride-event

    if (event->type() == QEvent::KeyPress)
    {
        auto keyEvent = static_cast<QKeyEvent *>(event);
        if (keyEvent->key() == Qt::Key_Tab || keyEvent->key() == Qt::Key_Backtab) {
            QApplication::postEvent(
                this, new QKeyEvent(keyEvent->type(), keyEvent->key(), keyEvent->modifiers()));
            return true;
        }
    }
    else if (event->type() == QEvent::FocusOut)
    {
        auto focusEvent = static_cast<QFocusEvent *>(event);
        QApplication::postEvent(this, new QFocusEvent(focusEvent->type(), focusEvent->reason()));
        return false;
    }
    return QWidget::eventFilter(object, event);
}