Implementing hierarchical table headers in Qt requires strategic customziation of both the data model and header view components. This approach enables multi-level column/row headers, cell merging, and styled content while maintaining optimal performance through native Qt mechanisms.

The solution involves extending QAbstractTableModel to manage header hierarchy and overriding QHeaderView for custom rendering. The data model stores a tree structure where each node represents a header cell, with span properties defining merged regions.

Key model implementation details:

QVariant MultiLevelModel::data(const QModelIndex &index, int role) const {
    if (!index.isValid()) return QVariant();
    
    HeaderNode *node = static_cast<HeaderNode*>(index.internalPointer());
    return node ? node->getContent(role) : QVariant();
}

Model index creation logic:

QModelIndex MultiLevelModel::index(int row, int col, const QModelIndex &parent) const {
    HeaderNode *parentNode = parent.isValid() ?
        static_cast<HeaderNode*>(parent.internalPointer()) : root;
    
    HeaderNode *childNode = parentNode->findChild(row, col);
    if (!childNode) childNode = parentNode->createChild(row, col);
    
    return createIndex(row, col, childNode);
}

Header view customization for merged cells:

QSize CustomHeaderView::sectionSizeFromContents(int section) const {
    auto *model = qobject_cast<const MultiLevelModel *>(this->model());
    if (!model) return QHeaderView::sectionSizeFromContents(section);
    
    int levels = (orientation() == Qt::Horizontal) ? model->rowCount() : model->columnCount();
    QSize size = QHeaderView::sectionSizeFromContents(section);
    
    for (int i = 0; i < levels; ++i) {
        QModelIndex cell = (orientation() == Qt::Horizontal) ?
            model->index(i, section) : model->index(section, i);
        
        QModelIndex colSpan = model->getHorizontalSpan(cell);
        QModelIndex rowSpan = model->getVerticalSpan(cell);
        
        if (colSpan.isValid()) {
            int start = colSpan.column();
            int count = colSpan.data(Qt::SpanRole).toInt();
            size.setWidth(calculateHorizontalSpan(start, count));
            if (orientation() == Qt::Vertical) i = start + count - 1;
        }
        
        if (rowSpan.isValid()) {
            int start = rowSpan.row();
            int count = rowSpan.data(Qt::SpanRole).toInt();
            size.setHeight(calculateVerticalSpan(start, count));
            if (orientation() == Qt::Horizontal) i = start + count - 1;
        }
    }
    return size;
}

Configuration examples for header properties:

// Horizontal header setup
horizontalHeader->setSpan(0, 0, 3, 0);
horizontalHeader->setSpan(0, 1, 2, 2);
horizontalModel->setData(horizontalModel->index(0, 0), "Primary Header", Qt::DisplayRole);
horizontalModel->setData(horizontalModel->index(2, 1), "Secondary Header", Qt::DisplayRole);

// Vertical header setup
verticalHeader->setSpan(0, 0, 0, 3);
verticalModel->setData(verticalModel->index(1, 0), "Row Group 1", Qt::DisplayRole);
verticalModel->setData(verticalModel->index(1, 1), "Row Subgroup", Qt::DisplayRole);

// Styling
horizontalHeader->setBackgroundColor(horizontalModel->index(0, 0), QColor(0xCFCFCF));
verticalHeader->setForegroundColor(verticalModel->index(1, 1), Qt::darkBlue);