QTreeWidget with column span

markus0211

Hi,

I am trying to create a tree widget with column span. I am using the approach from here: https://stackoverflow.com/questions/26739541/how-to-span-the-columns-of-a-qtreeview-in-c-qt

So far this is working as expected. However, there is a problem with columns where the resize mode is set to QHeaderView::Stretch. When I resize the window the text in the colum is somehow flickering.

I prepared a simple example:

#include <QTreeWidget>
#include <QStyledItemDelegate>

enum CustomRoles {
    ColumnSpanRole = Qt::UserRole + 1,
    PropertyRole,
};

class TreeWidgetItemDelegate : public QStyledItemDelegate {
    Q_OBJECT
public:
    TreeWidgetItemDelegate(QObject* pParent = nullptr) : QStyledItemDelegate(pParent) {
        m_pTreeView = dynamic_cast<QTreeView*>(parent());
    }
    ~TreeWidgetItemDelegate() override = default;

    void paint(QPainter *painter, const QStyleOptionViewItem &option, const QModelIndex &index) const override {
        QStyleOptionViewItem opt = option;

        if (index.data(ColumnSpanRole).isValid() && index.data(ColumnSpanRole).canConvert<int>()) {
            auto col_span = index.data(ColumnSpanRole).toInt();

            if (col_span == 0)
                return;

            int w = option.rect.width();
            for (auto i = 1; i < col_span; i++)
                w += m_pTreeView->columnWidth(index.column() + i);

            opt.rect.setWidth(w);
        }

        QStyledItemDelegate::paint(painter, opt, index);
    }

private:
    QTreeView* m_pTreeView = nullptr;
};

class TreeWidgetItem : public QTreeWidgetItem {
public:
    TreeWidgetItem(QTreeWidget* pTreeWidget, const QStringList &strings = {}) : QTreeWidgetItem(pTreeWidget, strings) {}
    TreeWidgetItem(QTreeWidgetItem* pParent, const QStringList &strings = {}) : QTreeWidgetItem(pParent, strings) {}
    ~TreeWidgetItem() override = default;

    void setText(int column, const QString &text, int column_span = 1) {
        setData(column, ColumnSpanRole, column_span);
        for (auto i = 1; i < column_span; i++)
            setData(column + i, ColumnSpanRole, 0);
        QTreeWidgetItem::setText(column, text);
    }
};

class TreeWidget : public QTreeWidget {
    Q_OBJECT
public:
    TreeWidget(QWidget* pParent = nullptr) : QTreeWidget(pParent) {
        setItemDelegate(new TreeWidgetItemDelegate(this));
    }
    ~TreeWidget() override = default;
};

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

    TreeWidget treeWidget;
    treeWidget.setColumnCount(5);

    treeWidget.header()->setSectionResizeMode(QHeaderView::Fixed);

    treeWidget.setColumnWidth(0, 100);
    treeWidget.setColumnWidth(1, 100);
    treeWidget.header()->setSectionResizeMode(2, QHeaderView::Stretch);
    treeWidget.setColumnWidth(3, 100);
    treeWidget.header()->setSectionResizeMode(4, QHeaderView::Stretch);

    TreeWidgetItem item(&treeWidget);
    item.setText(0, "Column 1");
    item.setText(1, "Column 1 & Column 2", 2);
    item.setText(3, "Column 3");
    item.setText(4, "Column 4");

    treeWidget.show();

    return a.exec();
}

Maybe someone can look into the code and see if I have done something wrong.
I am using Qt version 6.7.2.