QTreeWidget 设置自定义滚动条在合适的时候show或hide C++实现

可以通过继承QTreeWidget并覆盖重写其resizeEvent函数来实现自定义滚动条的显示和隐藏。在该函数中，可以根据QTreeWidget的大小和内容的高度与宽度计算出是否需要显示滚动条，然后通过调用setVerticalScrollBarPolicy和setHorizontalScrollBarPolicy函数来设置QTreeWidget的垂直和水平滚动条的可见性。以下是实现代码：

class CustomTreeWidget : public QTreeWidget
{
public:
    CustomTreeWidget(QWidget *parent = nullptr)
        : QTreeWidget(parent)
    {
        // 设置垂直和水平滚动条的样式
        m_scrollBarStyle = "QScrollBar:vertical, QScrollBar:horizontal{"
                           "background-color: #F5F5F5;"
                           "border: none;"
                           "width: 10px;"
                           "margin: 0px 0px 0px 0px;"
                           "}"
                           "QScrollBar::handle:vertical, QScrollBar::handle:horizontal{"
                           "background-color: #C0C0C0;"
                           "border-radius: 5px;"
                           "min-height: 30px;"
                           "}"
                           "QScrollBar::add-line:vertical, QScrollBar::add-line:horizontal,"
                           "QScrollBar::sub-line:vertical, QScrollBar::sub-line:horizontal{"
                           "background: none;"
                           "}"
                           "QScrollBar::add-page:vertical, QScrollBar::add-page:horizontal,"
                           "QScrollBar::sub-page:vertical, QScrollBar::sub-page:horizontal{"
                           "background: none;"
                           "}";

        // 设置滚动条样式表
        m_vScrollBar.setStyleSheet(m_scrollBarStyle);
        m_hScrollBar.setStyleSheet(m_scrollBarStyle);
    }

protected:
    void resizeEvent(QResizeEvent *event) override
    {
        QTreeWidget::resizeEvent(event);

        bool showVerticalScrollBar = verticalScrollBarPolicy() == Qt::ScrollBarAlwaysOn ||
                                     (verticalScrollBarPolicy() == Qt::ScrollBarAsNeeded && 
                                      contentsSize().height() > viewport()->height());
        bool showHorizontalScrollBar = horizontalScrollBarPolicy() == Qt::ScrollBarAlwaysOn ||
                                       (horizontalScrollBarPolicy() == Qt::ScrollBarAsNeeded && 
                                        contentsSize().width() > viewport()->width());

        if (showVerticalScrollBar) {
            // 显示垂直滚动条
            setVerticalScrollBarPolicy(Qt::ScrollBarAlwaysOn);
            m_vScrollBar.setParent(viewport());
            m_vScrollBar.setGeometry(viewport()->width() - m_vScrollBar.width(), 0, 
                                      m_vScrollBar.width(), viewport()->height());
            m_vScrollBar.setRange(0, contentsSize().height() - viewport()->height());
            m_vScrollBar.setSingleStep(verticalScrollBar()->singleStep());
            m_vScrollBar.setPageStep(viewport()->height());
            m_vScrollBar.setValue(verticalScrollBar()->value());
            connect(verticalScrollBar(), &QScrollBar::valueChanged, &m_vScrollBar, &QScrollBar::setValue);
            connect(&m_vScrollBar, &QScrollBar::valueChanged, verticalScrollBar(), &QScrollBar::setValue);
        } else {
            // 隐藏垂直滚动条
            setVerticalScrollBarPolicy(Qt::ScrollBarAlwaysOff);
            m_vScrollBar.setParent(nullptr);
        }

        if (showHorizontalScrollBar) {
            // 显示水平滚动条
            setHorizontalScrollBarPolicy(Qt::ScrollBarAlwaysOn);
            m_hScrollBar.setParent(viewport());
            m_hScrollBar.setGeometry(0, viewport()->height() - m_hScrollBar.height(), 
                                      viewport()->width(), m_hScrollBar.height());
            m_hScrollBar.setRange(0, contentsSize().width() - viewport()->width());
            m_hScrollBar.setSingleStep(horizontalScrollBar()->singleStep());
            m_hScrollBar.setPageStep(viewport()->width());
            m_hScrollBar.setValue(horizontalScrollBar()->value());
            connect(horizontalScrollBar(), &QScrollBar::valueChanged, &m_hScrollBar, &QScrollBar::setValue);
            connect(&m_hScrollBar, &QScrollBar::valueChanged, horizontalScrollBar(), &QScrollBar::setValue);
        } else {
            // 隐藏水平滚动条
            setHorizontalScrollBarPolicy(Qt::ScrollBarAlwaysOff);
            m_hScrollBar.setParent(nullptr);
        }
    }

private:
    QString m_scrollBarStyle;
    QScrollBar m_vScrollBar{Qt::Vertical};
    QScrollBar m_hScrollBar{Qt::Horizontal};
};

在使用时，只需要将原本的QTreeWidget替换为CustomTreeWidget即可：

CustomTreeWidget *treeWidget = new CustomTreeWidget(parent);