QT日常代码三

最新推荐文章于 2024-05-11 23:58:37 发布

翻译最新推荐文章于 2024-05-11 23:58:37 发布 · 420 阅读

本文探讨了Qt中事件处理的层次与调用顺序，并通过示例代码进行了验证。此外，还介绍了如何使用Qt进行渐变绘制及坐标系统的应用。

1、事件总结

为了进一步了解这几个层次的事件处理方式的调用顺序，我们通过这个测试代码：

class Label : public QWidget
{
public:
    Label()
    {
        installEventFilter(this);
    }

    bool eventFilter(QObject *watched, QEvent *event)
    {
        if (watched == this) {
            if (event->type() == QEvent::MouseButtonPress) {
                qDebug() << "eventFilter";
            }
        }
        return false;
    }

protected:
    void mousePressEvent(QMouseEvent *)
    {
        qDebug() << "mousePressEvent";
    }

    bool event(QEvent *e)
    {
        if (e->type() == QEvent::MouseButtonPress) {
            qDebug() << "event";
        }
        return QWidget::event(e);
    }
};

class EventFilter : public QObject
{
public:
    EventFilter(QObject *watched, QObject *parent = 0) :
        QObject(parent),
        m_watched(watched)
    {
    }

    bool eventFilter(QObject *watched, QEvent *event)
    {
        if (watched == m_watched) {
            if (event->type() == QEvent::MouseButtonPress) {
                qDebug() << "QApplication::eventFilter";
            }
        }
        return false;
    }

private:
    QObject *m_watched;
};

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);
    Label label;
    app.installEventFilter(new EventFilter(&label, &label));
    label.show();
    return app.exec();
}

运行结果：

2、渐变

绘制一个色轮（color wheel）：

void ColorWheel::paintEvent(QPaintEvent *)
{
    QPainter painter(this);
    painter.setRenderHint(QPainter::Antialiasing);

    const int r = 150;
    QConicalGradient conicalGradient(0, 0, 0);

    conicalGradient.setColorAt(0.0, Qt::red);
    conicalGradient.setColorAt(60.0/360.0, Qt::yellow);
    conicalGradient.setColorAt(120.0/360.0, Qt::green);
    conicalGradient.setColorAt(180.0/360.0, Qt::cyan);
    conicalGradient.setColorAt(240.0/360.0, Qt::blue);
    conicalGradient.setColorAt(300.0/360.0, Qt::magenta);
    conicalGradient.setColorAt(1.0, Qt::red);

    painter.translate(r, r);

    QBrush brush(conicalGradient);
    painter.setPen(Qt::NoPen);
    painter.setBrush(brush);
    painter.drawEllipse(QPoint(0, 0), r, r);
}

运行效果：

3、坐标系统

void PaintDemo::paintEvent(QPaintEvent *)
{
    QPainter painter(this);
    painter.fillRect(10, 10, 50, 100, Qt::red);
    painter.save();
    painter.translate(100, 0); // 向右平移 100px
    painter.fillRect(10, 10, 50, 100, Qt::yellow);
    painter.restore();
    painter.save();
    painter.translate(300, 0); // 向右平移 300px
    painter.rotate(30); // 顺时针旋转 30 度
    painter.fillRect(10, 10, 50, 100, Qt::green);
    painter.restore();
    painter.save();
    painter.translate(400, 0); // 向右平移 400px
    painter.scale(2, 3); // 横坐标单位放大 2 倍，纵坐标放大 3 倍
    painter.fillRect(10, 10, 50, 100, Qt::blue);
    painter.restore();
    painter.save();
    painter.translate(600, 0); // 向右平移 600px
    painter.shear(0, 1); // 横向不变，纵向扭曲 1 倍
    painter.fillRect(10, 10, 50, 100, Qt::cyan);
    painter.restore();
}

运行结果：