paintevent占cpu,在paintEvent中警告QPainter

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(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 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);

}

}

and I am taking these errors

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

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

解决方案

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

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.

So, instead of

QPainter painter(this);

write

QPainter painter(viewport());

The same could be seen in the source of QGraphicsView, i.e.:

// Set up the painter

QPainter painter(viewport());