警告QPainter在paintEvent内

Question

我试图在QChartView中绘制更多的信息，所以我重新实现了paintEvent。

  virtual void paintEvent(QPaintEvent *event) {
    QChartView::paintEvent(event);
    OmenChart *mchr = dynamic_cast<OmenChart *>(this->chart());
    if(mchr == nullptr)
        return;
    QPainter painter(this);

    const int labelOffset = 2 + 2;
    painter.setFont(this->font());
    painter.setPen(QPen(Qt::black));
    QFontMetrics fm(painter.font());


    const OmenScatterSeries *omnSr = mchr->serie();
    QVector<QPointF> points = omnSr->pointsVector();
    QStringList labels = omnSr->pointLabels();

    for (int i(0); i < labels.count(); i++) {
        QString pointLabel = labels[i];

        // Position text in relation to the point
        int pointLabelWidth = fm.width(pointLabel);
        QPointF position(points.at(i));
        position.setX(position.x() - pointLabelWidth / 2);
        position.setY(position.y() - labelOffset);
        painter.drawText(position, pointLabel);
    }
}

我要承担这些错误

QWidget::paintEngine: Should no longer be called
QPainter::begin: Paint device returned engine == 0, type: 1
QPainter::setFont: Painter not active
QPainter::setPen: Painter not active
QPainter::font: Painter not active
QWidget::paintEngine: Should no longer be called

对此有什么想法吗？我也使用了painter.begin和end，但是我也犯了同样的错误

Answer 1

不要使用QChartView的子类，而是使用它的视图。

QChartView是从QGraphicsView派生的，而后者又是从QAbstractScrollArea派生的，根据这个答案 (以及引用的文档)，您应该使用viewport作为QPainter的画图设备，而不是小部件本身。

所以，而不是

QPainter painter(this);

写

QPainter painter(viewport());

在QGraphicsView的来源中也可以看到同样的情况，即：

// Set up the painter
QPainter painter(viewport());