Custom QStyledItemDelegate with a checkBox, that does not center. How to debug?

[andi456]

Hi,

first of all, my modest aim is to write a custom QStyledItemDelegate with a CheckBox as editor for a TableView that colorizes the background under certain conditions.

Colorizing works, but using the checkBox does not. Whenever I click on a cell with the corresponding checkBox, another checkBox is being displayed to the left. What could be the cause of this? Where else should I place code to center the checkBox, that is being edited?

Thanks in advance,

Kind regards,

Andreas

[andi456]

@andi456 Here is my paint function, which I suspect to be the cause of the problem:

void CheckBoxZDelegate::paint(QPainter *painter, const QStyleOptionViewItem &option, const QModelIndex &index) const {
   QStyleOptionViewItem opt = option;
   int grad_spalte = this->get_idxFromHeader("Grad");
   int grad = this->get_intFromVariant(index.siblingAtColumn(grad_spalte).data(Qt::DisplayRole));
   if (grad==0) {
       this->paint_pro_grad(grad, cbud_grad_color_qvec, painter, opt.rect);
   } else if (grad==1) {
       this->paint_pro_grad(grad, cbud_grad_color_qvec, painter, opt.rect);
   } else if (grad==2) {
       this->paint_pro_grad(grad, cbud_grad_color_qvec, painter, opt.rect);
   } else if (grad==3) {
       this->paint_pro_grad(grad, cbud_grad_color_qvec, painter, opt.rect);
   } else if (grad==4) {
       this->paint_pro_grad(grad, cbud_grad_color_qvec, painter, opt.rect);
   } else if (grad==5) {
       this->paint_pro_grad(grad, cbud_grad_color_qvec, painter, opt.rect);
   } else if (grad==6) {
       this->paint_pro_grad(grad, cbud_grad_color_qvec, painter, opt.rect);
   } else if (grad==7) {
       this->paint_pro_grad(grad, cbud_grad_color_qvec, painter, opt.rect);
   } else if (grad==8) {
       this->paint_pro_grad(grad, cbud_grad_color_qvec, painter, opt.rect);
   } else if (grad==9) {
       this->paint_pro_grad(grad, cbud_grad_color_qvec, painter, opt.rect);
   }
   initStyleOption(&opt, index);
   auto * widget = opt.widget;
   auto * style = widget->style();
   int zeile = index.row();
   QVariant value = index.data(Qt::CheckStateRole);
  // if (!value.isValid())
   int cb_value = get_intFromVariant(value);
   //qDebug() << "Paint Method, index data " << cb_value;
   if ((style) && (zeile < index.model()->rowCount() - 1)) {
        /*QRect checkBoxRect=style->subElementRect(QStyle::SE_CheckBoxIndicator, &opt);
        int chkWidth=checkBoxRect.width();
        int chkHeight=checkBoxRect.height();

        int centerX=opt.rect.left() + qMax(opt.rect.width()/2-chkWidth/2, 0);
        int centerY=opt.rect.top() + qMax(opt.rect.height()/2-chkHeight/2, 0);
        opt.rect.moveTo(centerX, centerY);
        opt.rect.setSize(QSize(chkWidth, chkHeight));
        */
        opt.state.setFlag(QStyle::State_HasFocus, false);
        opt.features.setFlag(QStyleOptionViewItem::HasDisplay, true);
        opt.features.setFlag(QStyleOptionViewItem::HasDecoration, false);
        opt.features.setFlag(QStyleOptionViewItem::HasCheckIndicator, true);
        if (cb_value== Qt::Checked) {
            auto stateFlag = QStyle::State_On;
           opt.state.setFlag(stateFlag, true);
           //qDebug() << "STateFlag auf ON";
        } else {
            auto stateFlag = QStyle::State_Off;
            opt.state.setFlag(stateFlag, true);
          // qDebug() << "STateFlag auf Off";
        }
        opt.rect = this->getCheckBoxRect(opt);
        style->drawControl(QStyle::CE_ItemViewItem, &opt, painter, widget);
        //qDebug() << "Checkbox delegate paint method called";
        style->drawPrimitive(QStyle::PE_IndicatorItemViewItemCheck, &opt, painter, widget);
    } else {
        painter->setPen(Qt::black);
        //int spalte = index.column();
        opt.features.setFlag(QStyleOptionViewItem::HasCheckIndicator, false);
        //QVariant value =
        QString cell_text = index.model()->data(index, Qt::CheckStateRole).toString();
        qDebug() << "Painter Method: " << cell_text;
        //if (value.canConvert<QString>() && value.convert(QVariant::String)) {
            painter->drawText(opt.rect, Qt::AlignCenter, cell_text);
        //}
       //QString cell_text = QString::number(sum_Flags);
      // painter->drawText(opt.rect, Qt::AlignCenter, cell_text);
   }
}

[andi456]

@andi456 I see, setEditorData fetches the value from the corresponding model. What I am concerned about is the setModelData function....

Further investigation leads me to assume that i have to reimplement the editorEvent method as well. This post seems to indicate this.

It is a little counterintuitive that the activated editor is being drawn in a different position than the deactivated one.

[andi456]

@andi456 Just in case someone has a similar problem. The solution for me was indeed the hint given in the link above.

As can be seen from the posted paint method above, I use a function to determine the rectangle of the checkBox, which looks like this

QRect CheckBoxZBuchDeckDelegate::getCheckBoxRect(const QStyleOptionViewItem &option) const {
   QStyleOptionViewItem opt = option;
   auto widget = opt.widget;
   auto style = widget->style();
   auto checkboxSize = style->subElementRect(QStyle::SE_CheckBoxIndicator, &option, widget).size();
   return QStyle::alignedRect(option.direction, Qt::AlignCenter, checkboxSize, option.rect);
}

So I just used the same function in the eventEditor method copied from the qt-sources of qstyleditemdelegate.cpp
after deleting the lines containing

const QWidget *widget = QStyledItemDelegatePrivate::widget(option);
QStyle *style = widget ? widget->style() : QApplication::style();

I replaced

QRect checkRect = style->subElementRect(QStyle::SE_ItemViewItemCheckIndicator, &viewOpt, widget);

with

QRect checkRect = this->getCheckBoxRect(option);

et voilà.

If a QStyledItemDelegate should answer to an event, the area to be clicked has to be announced to the editorEvent too.