Centering DecorationRole icon in QTableView cell

ArmanSom

I've subclassed QStyledItemDelegate and overrode the paint function. Then, I set the delegate appropriately. Here is the paint override code below:

{
    QStyleOptionViewItem opt = option;
    opt.decorationAlignment = Qt::AlignHCenter;
    QStyledItemDelegate::paint(painter, opt, index);
}

Even so, the icon does not center. However, if I set:

opt.decorationPosition = QStyleOptionViewItem::Top;

...then the icon does center horizontally. However, it is pushed up to the "top" which is not what I want. How can I center my icon horizontally and vertically?

SGaist

Hi,

What if you use Qt::AlignCenter ?

ArmanSom

@SGaist Unfortunately, that makes no difference.

SGaist

Can you provide a minimal compilable sample that shows this ?

VRonin

Just to understand better, do you want the text to be painted overlapping the decoration?

ArmanSom

@SGaist Sure, here it is:

class Model : public QAbstractTableModel
{
    int rows;
    int columns;
    QIcon flagIcon;

  public:
    explicit Model(QObject * parent = nullptr) : QAbstractTableModel(parent)
    {
        rows = 3;
        columns = 3;
        flagIcon.addFile(QCoreApplication::applicationDirPath() + "/flag.png");
    }

    int rowCount(const QModelIndex &parent = QModelIndex()) const { return rows; }
    int columnCount(const QModelIndex &parent = QModelIndex()) const { return columns; }
    QVariant data(const QModelIndex &index, int role = Qt::DisplayRole) const
    {
        if (role == Qt::DecorationRole)
            return flagIcon;

        else return QVariant();
    }
};

class FlagDelegate : public QStyledItemDelegate
{
public:
    FlagDelegate(QObject * parent) : QStyledItemDelegate(parent) { }
    void paint(QPainter *painter, const QStyleOptionViewItem &option, const QModelIndex &index) const
    {
        QStyleOptionViewItem opt = option;
        opt.decorationAlignment = Qt::AlignCenter;
        QStyledItemDelegate::paint(painter, opt, index);
    }
};

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);

    QTableView table;
    table.setFixedWidth(400);
    table.setFixedHeight(400);

    Model model(&table);
    table.setModel(&model);

    FlagDelegate delegate(&table);
    table.setItemDelegate(&delegate);

    table.show();

    return a.exec();
}

Again, in the overridden paint method, the icon only centers if I set opt.decorationPosition to Top or Bottom.

ArmanSom

@VRonin Sure, if that's what it takes. That's somewhat inapplicable to my situation because I have only one column that displays icons, but it never displays text.

ArmanSom

The solution is to manually draw the pixmap of the icon with the painter object, like so:

void FlagDelegate::paint(QPainter *painter, const QStyleOptionViewItem &option, const QModelIndex &index) const
{
    QRect rect = option.rect;
    QIcon icon = qvariant_cast<QIcon>(index.data(Qt::DecorationRole));
    QPixmap pix = icon.pixmap( rect.size() *= 0.70 );

    QPoint p = QPoint((rect.width() - pix.width())/2, (rect.height() - pix.height())/2);
    painter->drawPixmap(rect.topLeft() + p, pix);
}

VRonin

void FlagDelegate::paint(QPainter *painter, const QStyleOptionViewItem &option, const QModelIndex &index) const
{
const QStyle* style = option.widget ? option.widget->style() : qApp->style();
style->drawPixmap(option.rect,Qt::AlignCenter,index.data(Qt::DecorationRole).value<QIcon>().pixmap(option.rect.size()));
}