代码这里就不细说了，有兴趣的可以自己研究研究。绘制规则就是上述4点

//绘制branch
{
    DataNode * node = static_cast<DataNode *>(index.internalPointer());
    bool hasChild = node->children().size() != 0;//是否有孩子

    QList<DataNode *> & children = node->parent()->children();
    bool has_next_siblings = children.indexOf(node) != (children.size() - 1);//是否有向后的兄弟
    bool has_pre_siblings = children.indexOf(node) != 0;//是否有向前的兄弟

    int level = node->level();
    int indentaion = indentation();//缩进
    int indentaions = indentaion * (level - 1);//缩进距离

    QRect r = rect;
    r.setLeft(r.left() + indentaions);//图标绘制位置

    painter->save();
    painter->setPen(m_branchLine);

    bool expaned = isExpanded(index);//节点是否展开

    QLine line(r.center() + QPoint(0, r.top() - r.center().y()), r.center() + QPoint(0, r.bottom() - r.center().y()));
    line.translate(-indentaion, 0);
    //QLine line(r.topLeft(), r.bottomLeft());
    //循环绘制(具有兄弟节点的)父节点向下的竖线
    DataNode * parent_node = node->parent();
    DataNode * sub_node = node;
    bool isNeed = node->children().size() == 0;
    for (int i = level - 1; i >= 0; --i)
    {
        QList<DataNode *> & children = parent_node->children();
        bool has_next_siblings = children.indexOf(sub_node) != (children.size() - 1);//父节点是否有(向后的)兄弟

        if (has_next_siblings)
        {
            painter->drawLine(line);
        }
        

        if (level - 1 == i)
        {
            QPoint pos = (line.p1() + line.p2()) / 2;
            QPoint pos2 = pos + QPoint(indentaion / 2, 0);

            painter->drawLine(pos, pos2);

            if (!has_next_siblings)
            {
                painter->drawLine(line.p1(), (line.p1() + line.p2()) / 2);
            }
        }

        sub_node = parent_node;
        parent_node = parent_node->parent();
        line.translate(-indentaion, 0);
    }

    QPixmap pix;
    if (expaned)
    {
        if (hasChild)
        {
            pix = QPixmap(":/branch-expand.png");
        }
    }
    else
    {
        if (hasChild)
        {
            pix = QPixmap(":/branch-collapse.png");
        }
    }
    if (pix.isNull() == false)
    {
        QRect pixRect = QRect(QPoint(0, 0), pix.size());
        pixRect.moveCenter(r.center());

        if (expaned)
        {
            QLine line(r.center(), r.center() + QPoint(0, r.bottom() - r.center().y()));
            painter->drawLine(line);
        }

        painter->drawPixmap(pixRect, pix);
    }

    painter->restore();
}

3、同步左侧表头

上一篇文章Qt实现表格树控件-支持多级表头 中已经说了，我们的表格控件是使用QTableView+QTreeView来实现的，那么我们操作树控件时必然要对表格中的表头进行同步操作了。

树控件折叠时隐藏垂直表头指定行

void collapsed_p(DataNode * node)
{
    QList<DataNode *> childNodeList = node->children();
    //DataManager::getInstance()->allChildNode(node, childNodeList);

    int size = childNodeList.size();
    for (int i = 0; i < size; ++i)
    {
        int serial = DataManager::getInstance()->serialNoOfNode(childNodeList.at(i));
        VHeaderView::instance->SetRowHide(serial, true);

        QModelIndex subIndex = FrozenTreeView::instance->rowIndex(serial);

        collapsed_p(childNodeList.at(i));
    }
}

void FrozenTreeView::onCollapsed(const QModelIndex & index)
{
    if (!index.isValid())
        return;

    DataNode * node = static_cast<DataNode*>(index.internalPointer());
    if (nullptr == node)
        return;

    collapsed_p(node);
    VHeaderView::instance->UpdateCache();

    //要对水平头的最后一列进行重设大小，引起水平头自己的更新操作，从而使整个界面显示正确
    HHeaderView::instance->resizeLastSection(true);
}