How can I center QCheckBox in QTableView?

[CuriousPan]

@Christian-Ehrlicher, hey, this is a really nice example, but I don't understand what 'role' should I use in the model to center the checkbox, because now it's in the left top corner.

[JonB]

@CuriousPan
The code at @Christian-Ehrlicher's https://wiki.qt.io/Center_a_QCheckBox_or_Decoration_in_an_Itemview tells you what role it is using

As alignment indicator the Qt::TextAlignmentRole is 'misused' since no text is drawn for the cell.

and you can see it in the code you are copying:

opt.rect = QStyle::alignedRect(opt.direction, index.data(Qt::TextAlignmentRole).value<Qt::Alignment>(), rect.size(), opt.rect);

Or use your own role if you don't want to use that.

[CuriousPan]

@JonB, yeees, I understood this and I was using Qt::TextAlignmentRole and returning Qt::AlignCenter, but for some reason it's not aligned :(

[JonB]

@CuriousPan
I do not know about the behaviour of the delegate. But if you want to know to know whether it is being "triggered" and recognises the role in question put in a qDebug() statement (in the delegate) to find out.

[CuriousPan]

This post is deleted!

[CuriousPan]

@JonB, yes, it's defenitely triggered.

[JonB]

@CuriousPan
Find all your occurrences of

QStyle::alignedRect(opt.direction, index.data(Qt::TextAlignmentRole).value<Qt::Alignment>(), rect.size(), opt.rect)

and qDebug() << index.data(Qt::TextAlignmentRole).value<Qt::Alignment>().

[CuriousPan]

@JonB, it always retruns QFlags<Qt::AlignmentFlag>() 1 which is Qt::DecorationRole, right?

[raven-worx]

@CuriousPan said in How can I center QCheckBox in QTableView?:

it always retruns QFlagsQt::AlignmentFlag() 1 which is Qt::DecorationRole, right

the Qt::AlignmentFlag flags/enum doesnt contain Qt::DecorationRole, so no
https://doc.qt.io/qt-5/qt.html#AlignmentFlag-enum

[CuriousPan]

@raven-worx, oh, I see. You're right. Anyway, why is that so?

[CuriousPan]

@raven-worx, wait! I confused you and me. This '1' is my custom printout. So what you suggested printing just gives following output: QFlags<Qt::AlignmentFlag>()

[JonB]

@CuriousPan
Qt::AlignLeft 0x0001 Aligns with the left edge.

So this value 1 is left alignment, just as per your picture, and no kind of centering specified, which would have value 4.

[CuriousPan]

@JonB, yeah, it is, but as I said, no numbers are printed.

[JonB]

@CuriousPan said in How can I center QCheckBox in QTableView?:

@JonB, it always retruns QFlagsQt::AlignmentFlag() 1 which is Qt::DecorationRole, right?

That's what you wrote. See that 1? Can you please concentrate on one thing at a time.

[CuriousPan]

@JonB, yep, I can. I'm really sorry for confusing you. No 1 is printed, it's just my mistake.

[JonB]

@CuriousPan
So that would be the value for left-align. Either you are not setting or returning the desired "center" flag on your item for the Qt::TextAlignmentRole --- you have to do that if you want it centered, that's what the code does --- or you are not looking at the right item/index.

[CuriousPan]

@JonB, I guess you're right, but, as I showed on this screenshot:
I'm using the correct role and column is defenitely correct (checked usingqDebug()).

[JonB]

@CuriousPan

• Print out index.column() in the delegate.
• Print out RecurrentColumn.
• Put a qDebug() just above return Qt::AlignCenter in your "screenshot" to make sure it's being hit.
• Please don't paste code as screenshots, paste it as code. Show where you have that code and what is above the extract you show.

[CuriousPan]

@JonB

• index.column() in the delegate has the proper number. 4 in my case as long as it is 4th (starting from 0) column in the table view.
• What do you mean by printing RecurrentColumn?

//checking other roles
} else if (index.isValid() && role == Qt::TextAlignmentRole) { 
         switch (index.column()) { 
         case RecurrentColumn: 
              qDebug() << "Hit"; 
              return Qt::AlignCenter; 
         case TotalColumn: 
              return {Qt::AlignRight | Qt::AlignVCenter}; 
         case PlnTotalColumn: 
              return {Qt::AlignRight | Qt::AlignVCenter}; 
         return Qt::AlignCenter; 
         }
}
// "Hit" is getting printed.

• Okay, will try to value your time and effort :)

[CuriousPan]

@CuriousPan I have fixed the issue.
I used pretty dirty, but working trick: set Qt::AlignedCenter right in the delegate:

void CenteredCheckBoxDelegate::paint(QPainter *painter, const QStyleOptionViewItem &option, const QModelIndex &index) const
{
    QStyleOptionViewItem opt = option;
    const QWidget *widget = option.widget;
    initStyleOption(&opt, index);
    QStyle *style = opt.widget ? opt.widget->style() : QApplication::style();
    style->drawPrimitive(QStyle::PE_PanelItemViewItem, &opt, painter, widget);
    if (opt.features & QStyleOptionViewItem::HasCheckIndicator) {
        switch (opt.checkState) {
        case Qt::Unchecked:
            opt.state |= QStyle::State_Off;
            break;
        case Qt::PartiallyChecked:
            opt.state |= QStyle::State_NoChange;
            break;
        case Qt::Checked:
            opt.state |= QStyle::State_On;
            break;
        }
        auto rect = style->subElementRect(QStyle::SE_ItemViewItemCheckIndicator, &opt, widget);
        opt.rect = QStyle::alignedRect(opt.direction, Qt::AlignCenter/*index.data(Qt::TextAlignmentRole).value<Qt::Alignment>()*/, rect.size(), opt.rect);
        opt.state = opt.state & ~QStyle::State_HasFocus;
        style->drawPrimitive(QStyle::PE_IndicatorItemViewItemCheck, &opt, painter, widget);
    } else if (!opt.icon.isNull()) {
        // draw the icon
        QRect iconRect = style->subElementRect(QStyle::SE_ItemViewItemDecoration, &opt, widget);
        iconRect = QStyle::alignedRect(opt.direction, Qt::AlignCenter/*index.data(Qt::TextAlignmentRole).value<Qt::Alignment>()*/, iconRect.size(), opt.rect);
        QIcon::Mode mode = QIcon::Normal;
        if (!(opt.state & QStyle::State_Enabled))
            mode = QIcon::Disabled;
        else if (opt.state & QStyle::State_Selected)
            mode = QIcon::Selected;
        QIcon::State state = opt.state & QStyle::State_Open ? QIcon::On : QIcon::Off;
        opt.icon.paint(painter, iconRect, opt.decorationAlignment, mode, state);
    } else {
        QStyledItemDelegate::paint(painter, option, index);
    }
}

bool CenteredCheckBoxDelegate::editorEvent(QEvent *event, QAbstractItemModel *model, const QStyleOptionViewItem &option, const QModelIndex &index)
{
    Q_ASSERT(event);
    Q_ASSERT(model);
    // make sure that the item is checkable
    Qt::ItemFlags flags = model->flags(index);
    if (!(flags & Qt::ItemIsUserCheckable) || !(option.state & QStyle::State_Enabled) || !(flags & Qt::ItemIsEnabled))
        return false;
    // make sure that we have a check state
    QVariant value = index.data(Qt::CheckStateRole);
    if (!value.isValid())
        return false;
    const QWidget *widget = option.widget;
    QStyle *style = option.widget ? widget->style() : QApplication::style();
    // make sure that we have the right event type
    if ((event->type() == QEvent::MouseButtonRelease) || (event->type() == QEvent::MouseButtonDblClick) || (event->type() == QEvent::MouseButtonPress)) {
        QStyleOptionViewItem viewOpt(option);
        initStyleOption(&viewOpt, index);
        QRect checkRect = style->subElementRect(QStyle::SE_ItemViewItemCheckIndicator, &viewOpt, widget);
        checkRect = QStyle::alignedRect(viewOpt.direction, Qt::AlignCenter/*index.data(Qt::TextAlignmentRole).value<Qt::Alignment>()*/, checkRect.size(), viewOpt.rect);
        QMouseEvent *me = static_cast<QMouseEvent *>(event);
        if (me->button() != Qt::LeftButton || !checkRect.contains(me->pos()))
            return false;
        if ((event->type() == QEvent::MouseButtonPress) || (event->type() == QEvent::MouseButtonDblClick))
            return true;
    } else if (event->type() == QEvent::KeyPress) {
        if (static_cast<QKeyEvent *>(event)->key() != Qt::Key_Space && static_cast<QKeyEvent *>(event)->key() != Qt::Key_Select)
            return false;
    } else {
        return false;
    }
    Qt::CheckState state = static_cast<Qt::CheckState>(value.toInt());
    if (flags & Qt::ItemIsUserTristate)
        state = ((Qt::CheckState)((state + 1) % 3));
    else
        state = (state == Qt::Checked) ? Qt::Unchecked : Qt::Checked;
    return model->setData(index, state, Qt::CheckStateRole);
}

Thanks everyone who took part in the discussion.