QPainter won't draw

[Chick3nN00dleS0up]

I've got a class "ComponentArea" which is derived from QScrollArea. The ComponentArea has some other QWidget-derivatives in it.
I modify the palette and enable mouseTracking in the constructor:

ComponentArea::ComponentArea(QWidget* parent) : QScrollArea(parent)
{
    QPalette palette = this->palette();

    palette.setColor(QPalette::Base, Qt::white);
    palette.setColor(QPalette::Window, Qt::white);
    palette.setColor(QPalette::AlternateBase, Qt::white);

    this->setPalette(palette);
    this->setMouseTracking(true);
}

The mouseMoveEvent calls repaint(), which triggers the paintEvent:

void ComponentArea::mouseMoveEvent(QMouseEvent *event)
{
    if(pressedSocket_first != 0)
    {
        mousePos_global = event->globalPos();
        this->repaint();
    }
}

void ComponentArea::paintEvent(QPaintEvent *event)
{
    Q_UNUSED(event)

    QPainter* painter = new QPainter(this);
    painter->eraseRect(QRect(QPoint(0,0), QPoint(this->size().width(), this->size().height())));
    painter->setPen(QPen(Qt::black, 1, Qt::SolidLine, Qt::SquareCap));

    if(pressedSocket_first != 0)
    {

        QPoint socketPos = this->mapFromGlobal(pressedSocket_first->mapToGlobal(QPoint(0,0)));
        socketPos.setX(socketPos.x() + pressedSocket_first->size().width() /2);
        socketPos.setY(socketPos.y() + pressedSocket_first->size().height() /2);

        QPoint mousePos = this->mapFromGlobal(mousePos_global);

        painter->drawLine(socketPos, mousePos);
    }
}

The line does not appear. With debugging, I made sure that drawLine() is in fact reached and the values of socketPos and mousePos make sense. Nevertheless the line does not appear. What am I doing wrong? Thanks in advance!

[mcosta]

Hi and welcome to devnet,

QPainter paints only when endPaint() is called (the destructor calls endPaint as well).
I suggest to change your code using a stack variable instead a pointer QPainter painter instead of QPainte *painter also because you never delete created painter

[Chick3nN00dleS0up]

@mcosta Hm, neither calling painter->end() manually nor using a "usual" variable solves it. I draw in the ComponentView's children the same way, and it works perfectly.