qt 自定义旋钮实现三个挡位的功能不使用QDial

如果您不想使用QDial控件，也可以使用QPainter和QMouseEvent来实现自定义旋钮并实现三个挡位的功能。以下是一个示例实现：

class CustomKnob : public QWidget
{
public:
    CustomKnob(QWidget *parent = nullptr) : QWidget(parent)
    {
        setFixedSize(100, 100);
        m_value = 0;
        m_notches = 3;
    }

    void paintEvent(QPaintEvent *event) override
    {
        QPainter painter(this);
        painter.setRenderHint(QPainter::Antialiasing, true);

        // 绘制背景圆形
        painter.setPen(Qt::NoPen);
        painter.setBrush(QColor("#dcdcdc"));
        painter.drawEllipse(rect().center(), 40, 40);

        // 绘制指针
        painter.setBrush(QColor("#ff7f50"));
        painter.save();
        painter.translate(rect().center());
        painter.rotate(m_value * 360 / 100.0);
        painter.drawConvexPolygon(QPolygonF(QVector<QPointF>() << QPointF(-20, 0) << QPointF(0, -50) << QPointF(20, 0)));
        painter.restore();

        // 绘制挡位
        painter.setPen(QPen(QColor("#ff7f50"), 3));
        qreal step = 360.0 / m_notches;
        for (int i = 0; i < m_notches; ++i) {
            painter.save();
            painter.translate(rect().center());
            painter.rotate(i * step);
            painter.drawLine(QPointF(0, -30), QPointF(0, -40));
            painter.restore();
        }
    }

    void mousePressEvent(QMouseEvent *event) override
    {
        if (event->button() == Qt::LeftButton) {
            QPoint center = rect().center();
            qreal angle = atan2(event->y() - center.y(), event->x() - center.x()) * 180 / M_PI + 90;
            if (angle < 0)
                angle += 360;
            qreal step = 360.0 / m_notches;
            if (angle < step / 2 || angle >= 360 - step / 2)
                m_value = 0;
            else if (angle < 180 - step / 2)
                m_value = 50;
            else
                m_value = 100;
            update();
        }
        QWidget::mousePressEvent(event);
    }

private:
    int m_value;
    int m_notches;
};

在这个示例中，我们继承自QWidget，并重写了paintEvent()和mousePressEvent()方法。在paintEvent()方法中，我们使用QPainter绘制了背景圆形、指针和挡位。在mousePressEvent()方法中，我们通过计算鼠标点击的角度来设置不同的挡位，并更新控件的值。您可以根据需要更改设置挡位的逻辑，并根据您的具体需求进行自定义。