How to center a column with a checkbox in QTableView?

[VRonin]

Try something like this:

#include <QApplication>
#include <QTableWidget>
#include <QStandardItemModel>
#include <QProxyStyle>
#include <QStyleOptionViewItem>
enum {
  CheckAlignmentRole = Qt::UserRole + Qt::CheckStateRole + Qt::TextAlignmentRole
};
class CenteredBoxProxy : public QProxyStyle{
public:
    QRect subElementRect(QStyle::SubElement element, const QStyleOption *option, const QWidget *widget) const override{
        const QRect baseRes = QProxyStyle::subElementRect(element, option, widget);
        if(element==SE_ItemViewItemCheckIndicator){
            const QStyleOptionViewItem* const itemOpt = qstyleoption_cast<const QStyleOptionViewItem*>(option) ;
            Q_ASSERT(itemOpt);
            const QVariant alignData = itemOpt->index.data(CheckAlignmentRole);
            if(alignData.isNull())
               return baseRes;
            const QRect itemRect = option->rect;
            Q_ASSERT(itemRect.width()>baseRes.width() && itemRect.height()>baseRes.height());
            const int alignFlag = alignData.toInt();
            int x=0,y=0;
            if(alignFlag & Qt::AlignLeft){
                x=baseRes.x();
            }
            else if(alignFlag & Qt::AlignRight){
                x=itemRect.x() + itemRect.width() - (baseRes.x()-itemRect.x())-baseRes.width();
            }
            else if(alignFlag & Qt::AlignHCenter){
                x=itemRect.x() + (itemRect.width()/2)-(baseRes.width()/2);
            }
            return QRect(QPoint(x,baseRes.y()), baseRes.size());
        }
        return baseRes;
    }
};

int main(int argc, char **argv)
{
    QApplication app(argc,argv);
    app.setStyle(new CenteredBoxProxy);
    QTableView wid;
    QStandardItemModel* model = new QStandardItemModel(&wid);
    model->insertColumns(0,3);
    model->insertRows(0,10);
    for(int i=0;i<10;++i){
        model->setData(model->index(i,0), i%2==0 ? Qt::Unchecked : Qt::Checked, Qt::CheckStateRole);
        model->setData(model->index(i,0), Qt::AlignCenter, CheckAlignmentRole);
        model->setData(model->index(i,1), i%2==0 ? Qt::Unchecked : Qt::Checked, Qt::CheckStateRole);
        model->setData(model->index(i,2), i);
        Q_ASSERT(model->item(i,0));
        model->item(i,0)->setFlags(model->item(i,0)->flags() | Qt::ItemIsUserCheckable);
    }
    wid.setModel(model);

    wid.show();
    return app.exec();
}

[Robert Hairgrove]

@VRonin ... THANK YOU! This works very well.

[Robert Hairgrove]

I saw this in qstyle.h in the "enum SubElement":

    SE_ViewItemCheckIndicator, // ### Qt 6: remove
    SE_ItemViewItemCheckIndicator = SE_ViewItemCheckIndicator,

...
I assume that SE_ItemViewItemCheckIndicator is safe to continue to use?

[SGaist]

Hi,

Yes it is.

[Robert Hairgrove]

I have adapted the code a little bit to take care of the focus rectangle which is also centered now. Of course, I will include a link to this forum topic in my code, which will be open source (thanks again, @VRonin :)

#ifndef CENTEREDBOXPROXY_HPP
#define CENTEREDBOXPROXY_HPP

#include <QProxyStyle>
#include <QStyleOptionViewItem>

enum {
  CheckAlignmentRole = Qt::UserRole
                     + Qt::CheckStateRole
                     + Qt::TextAlignmentRole
};

class CenteredBoxProxy : public QProxyStyle {
public:
  QRect subElementRect(QStyle::SubElement element,
                       const QStyleOption *option,
                       const QWidget *widget) const override {
    const QRect baseRes = QProxyStyle::subElementRect(element, option, widget);
    const QRect itemRect = option->rect;
    QRect retval = baseRes;
    QSize sz = baseRes.size();

    const QStyleOptionViewItem* const
        itemOpt = qstyleoption_cast<const QStyleOptionViewItem*>(option);

    if (itemOpt) {
      const QVariant alignData = itemOpt->index.data(CheckAlignmentRole);
      if(!alignData.isNull()) {
        const uint alignFlag = alignData.toUInt();
        if (alignFlag & Qt::AlignHCenter) {
          if (element == SE_ItemViewItemCheckIndicator) {
            int x = itemRect.x() + (itemRect.width()/2) - (baseRes.width()/2);
            retval = QRect( QPoint(x, baseRes.y()), sz);
          } else if (element == SE_ItemViewItemFocusRect) {
            sz.setWidth(baseRes.width()+baseRes.x());
            retval = QRect( QPoint(0, baseRes.y()), sz);
          }
        }
      }
    }
    return retval;
  }
};

#endif

[SGaist]

Thanks for the update !

[VRonin]

@Robert-Hairgrove said in How to center a column with a checkbox in QTableView?:

retval = QRect( QPoint(0, baseRes.y()), sz);

This seams dodgy. Could you try making the second column the one with the centred checkbox and see if it still works as expected

[Robert Hairgrove]

@VRonin ... Looks OK to me. But thanks for the suggestion, because I should have tried this myself before posting the update (and I hadn't).

The normal behavior for item views seems to be this:

1. When the widget has focus, the view item's focus indicator fills out the background of the entire item rectangle and is darker in color (e.g. when navigating the view with the arrow keys);
2. When the widget goes out of focus (e.g. clicking outside of the entire widget), there is another focus indicator which is shown, lighter in color, but only over the text normally accompanying the checkbox -- not over the checkbox itself.

When the checkbox has no text (i.e. when it is centered), this seems a little odd. This update "fixes" the non-focussed focus rectangle. :)

[VRonin]

Sorry I should have been more specific, my only concern is on having 0 as first argument to QPoint there as I think it's in coordinates of the scrollarea not of the item itself so my concern is that if the checkbox is in any column except the first column, retval would still point somewhere in the first column

[Alexey Serebryakov]

@A-A-SEZEN It does not work.

[A.A.SEZEN]

@Alexey-Serebryakov .. I am actively using those codes. With only one difference. QTableWidget instead of QTableView.

                    else if(yapi->slAlan[i] == "ISLEM") {
                        auto * checkWidget = new QWidget(this);
                        auto * check = new QCheckBox(this);
                        auto * checkLayout = new QHBoxLayout(checkWidget);
                        checkLayout->addWidget(check);
                        checkLayout->setAlignment(Qt::AlignCenter);
                        checkLayout->setContentsMargins(0,0,0,0);
                        check->setMaximumWidth(yapi->slColumnWidth[i].toInt());
                        check->setChecked(q.value(yapi->slAlan[i]).toString() == "2");
                        check->setCheckable(!bPasif);
                        if(!renk.isEmpty()) {
                            checkWidget->setStyleSheet(tr("background-color: %1").arg(renk));
                        }
                        tablo->setCellWidget(iSatir, i, checkWidget);
                        checkWidget->setContextMenuPolicy(Qt::CustomContextMenu);
                        connect(checkWidget, &QMenu::customContextMenuRequested, this, &kucukbas::doganPopupMenu);
                        connect(check, &QCheckBox::stateChanged, this, [=]() {
                            doganKaydet("ISLEM",
                                        check->isChecked() ? "2" : "0",
                                        idDogan());
                        });
                    }