在paintEvent中警告QPainter [英] Warning QPainter inside paintEvent

问题描述

我试图在QChartView中绘制更多信息，所以我重新实现paintEvent

I tried to draw some more information in QChartView so I re-implement 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);
    }
}

我正在处理这些错误

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

对此有何想法?我也用过painter.begin和end，但是我犯了同样的错误

Any ideas on this ? I had also used painter.begin and end but I took the same errors

推荐答案

请勿在 QChartView 的子类上绘制，而应在其视口上绘制.

Do not draw on your subclass of QChartView, but instead on its viewport.

QChartView 源自此答案(以及如文档所述)，您应该将视口用作绘画您的 QPainter 设备，而不是小部件本身.

QChartView is derived from QGraphicsView, which in turn is derived from QAbstractScrollArea and according to this answer (as well as the cited there documentation) you should use the viewport as a paint device for your QPainter, not the widget itself.

所以，而不是

QPainter painter(this);

写

QPainter painter(viewport());

在 QGraphicsView的来源，即:

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

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