qt 自定义旋钮

在 Qt 中，可以通过自定义绘制实现一个旋钮。以下是一个简单的例子：

1. 定义一个自定义旋钮控件类，继承自 QWidget。

2. 在控件类中定义旋钮的属性，如当前值、最小值、最大值、步长等。

3. 重写 paintEvent() 函数，在函数中使用 QPainter 绘制旋钮。

4. 重写 mousePressEvent() 和 mouseMoveEvent() 函数，实现旋钮的交互操作，如拖动旋钮改变值。

以下是一个简单的自定义旋钮控件的示例代码：

class Knob : public QWidget
{
    Q_OBJECT

public:
    explicit Knob(QWidget *parent = nullptr);

    void setValue(int value);
    int value() const;
    void setMinimum(int minimum);
    int minimum() const;
    void setMaximum(int maximum);
    int maximum() const;
    void setSingleStep(int step);
    int singleStep() const;

signals:
    void valueChanged(int value);

protected:
    void paintEvent(QPaintEvent *event) override;
    void mousePressEvent(QMouseEvent *event) override;
    void mouseMoveEvent(QMouseEvent *event) override;

private:
    int m_value;
    int m_minimum;
    int m_maximum;
    int m_singleStep;
    QPoint m_center;
    int m_radius;
    int m_angle;
};

Knob::Knob(QWidget *parent)
    : QWidget(parent)
    , m_value(0)
    , m_minimum(0)
    , m_maximum(100)
    , m_singleStep(1)
    , m_center(width() / 2, height() / 2)
    , m_radius(qMin(width(), height()) / 2 - 10)
    , m_angle(0)
{
    setSizePolicy(QSizePolicy::MinimumExpanding, QSizePolicy::MinimumExpanding);
}

void Knob::setValue(int value)
{
    if (value < m_minimum)
        value = m_minimum;
    if (value > m_maximum)
        value = m_maximum;
    if (value != m_value) {
        m_value = value;
        emit valueChanged(m_value);
        update();
    }
}

int Knob::value() const
{
    return m_value;
}

void Knob::setMinimum(int minimum)
{
    m_minimum = minimum;
}

int Knob::minimum() const
{
    return m_minimum;
}

void Knob::setMaximum(int maximum)
{
    m_maximum = maximum;
}

int Knob::maximum() const
{
    return m_maximum;
}

void Knob::setSingleStep(int step)
{
    m_singleStep = step;
}

int Knob::singleStep() const
{
    return m_singleStep;
}

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

    // 绘制外圆
    painter.save();
    painter.translate(m_center);
    painter.setPen(QPen(Qt::black, 2));
    painter.drawEllipse(QPoint(0, 0), m_radius, m_radius);
    painter.restore();

    // 绘制刻度线
    painter.save();
    painter.translate(m_center);
    painter.rotate(-120);
    for (int i = 0; i <= 20; ++i) {
        if (i % 2 == 0) {
            painter.drawLine(0, m_radius - 10, 0, m_radius - 20);
            painter.drawText(-10, m_radius - 22, QString::number(i * 5));
        } else {
            painter.drawLine(0, m_radius - 15, 0, m_radius - 20);
        }
        painter.rotate(6);
    }
    painter.restore();

    // 绘制指针
    painter.save();
    painter.translate(m_center);
    painter.rotate(-120 + m_angle);
    painter.setPen(QPen(Qt::red, 3));
    painter.drawLine(0, 0, m_radius - 30, 0);
    painter.restore();
}

void Knob::mousePressEvent(QMouseEvent *event)
{
    if (event->button() == Qt::LeftButton) {
        m_center = QPoint(width() / 2, height() / 2);
        m_radius = qMin(width(), height()) / 2 - 10;
        m_angle = qRound(qRadiansToDegrees(qAtan2(event->y() - m_center.y(), event->x() - m_center.x())));
    }
}

void Knob::mouseMoveEvent(QMouseEvent *event)
{
    if (event->buttons() & Qt::LeftButton) {
        int newAngle = qRound(qRadiansToDegrees(qAtan2(event->y() - m_center.y(), event->x() - m_center.x())));
        int delta = newAngle - m_angle;
        if (delta > 180)
            delta -= 360;
        if (delta < -180)
            delta += 360;
        setValue(m_value + delta / 2);
        m_angle = newAngle;
    }
}

在使用时，可以像使用其他控件一样添加到窗口中，并连接 valueChanged() 信号以处理旋钮的值改变事件。

Knob *knob = new Knob(this);
knob->setGeometry(50, 50, 100, 100);
connect(knob, &Knob::valueChanged, [=](int value) {
    qDebug() << "value: " << value;
});