Set QItemDelegate on a particular QTreeWidgetItem

Question

Is it possible to set a QItemDelegate on a particular QTreeWidgetItem? I need to color some of the QTreeWidgetItems with a particular color.

I assume it is possible as we have QAbstractItemView::setItemDelegateForRow but I can't figure out how. I can't use QAbstractItemView::setItemDelegateForRow because I need to set a custom delegate on a child row inside the QTreeWidget.

Does anyone know a solution for that?

Answer 1

You can access the QTreeWidget from you delegate's paint routine to check if a condition for painting the background is met

void custom_delegate::paint(QPainter* painter, const QStyleOptionViewItem& option, const QModelIndex& index) const
{
    const QTreeWidget* tree_widget = qobject_cast<const QTreeWidget*>(qstyleoption_cast<const QStyleOptionViewItemV3*>(&option)->widget);
    ....
}

or you store something in the QModelIndex UserData as Chernobyl suggested. In that case I would however create an enum for flags (if this is applicable in your case):

enum custom_painter_flags{
    paint_default = 0,
    paint_background = 1
};

void somewhere_creating_the_items()
{
    QTreeWidgetItem* newitem = new QTreeWidgetItem(...);
    newitem->setData(0, Qt::UserRole, QVariant::fromValue<int>(custom_painter_flags::paint_background));
}

void custom_delegate::paint(QPainter* painter, const QStyleOptionViewItem& option, const QModelIndex& index) const
{
    custom_painter_flags painter_flags = static_cast<painter>(index.data(Qt::UserRole).value<int>());

    if(painter_flags & paint_background){
        ....
    }
}

Unfortunately I have not much time right now so this is thrown together pretty quick. Feel free to edit if you find any errors.