Qt5 paintEvent not called inside QScrollArea - c++

Question

I'm having a bit of a problem with Qt. I'm trying to create a 2D drawing of cells, with QRect, by overloading paintEvent for a custom class which inherits QWidget and which is placed inside a QScrollArea. The problem is, paintEvent does not trigger at all (not on resize events, not when I call repaint() or update(), nor when I launch my program). Here is where I overload paintEvent, in GOL.cpp:
void GOL::paintEvent(QPaintEvent *) {
QPainter painter(this);
//painter.setPen(Qt::black);
int x1Rect = rectPaint.x();
int y1Rect = rectPaint.y();
int x2Rect = x1Rect + rectPaint.width();
int y2Rect = y1Rect + rectPaint.height();
int xCell;
int yCell = 0;
for (int i = 0; i < rows; i++) {
xCell = 0;
for (int j = 0; j < cols; j++) {
if (xCell <= x2Rect && yCell <= y2Rect && xCell + cellSize >= x1Rect &&
yCell + cellSize >= y1Rect) {
if (principalMatrix->get(i,j)) {
painter.fillRect(xCell, yCell, cellSize - 1, cellSize - 1, cellColourAlive);
}
else {
painter.fillRect(xCell, yCell, cellSize - 1, cellSize - 1, cellColourDead);
}
}
xCell += cellSize;
}
yCell += cellSize;
}
}
And my layout is as follows, in DisplayGame.cpp:
DisplayGame::DisplayGame(QWidget *parent, int threads_no, int generations, char* file_in, char* file_out) :
QWidget(parent) {
gol = new GOL(threads_no, generations, file_in, file_out);
QHBoxLayout *title = setupTitle();
QHBoxLayout *buttons = setupButtons();
QVBoxLayout *layout = new QVBoxLayout();
scrlArea = new QScrollArea;
scrlArea->setWidget(gol);
layout->addLayout(title);
layout->addWidget(scrlArea);
layout->addLayout(buttons);
setLayout(layout);
}
I honestly have no idea why it does not draw anything. Any ideas?

Answer 1

I've fixed it by modifying as follows:
DisplayGame::DisplayGame(QWidget *parent, int threads_no, int generations, char* file_in, char* file_out) :
QWidget(parent) {
gol = new GOL(this, threads_no, generations, file_in, file_out);
QSize *adjustSize = new QSize(gol->cellSize, gol->cellSize); //QSize object that is as big as my QRect matrix
adjustSize->setWidth(gol->cellSize * gol->rows);
adjustSize->setHeight(gol->cellSize * gol->cols);
gol->setMinimumSize(*adjustSize);
QVBoxLayout *layout = new QVBoxLayout;
QHBoxLayout *title = setupTitle();
layout->addLayout(title);
QHBoxLayout *buttons = setupButtons();
layout->addLayout(buttons);
QPalette pal(palette()); //Setting the background black, so the white spaces between QRect items cannot be seen (though I could have modified the margins?)
pal.setColor(QPalette::Background, Qt::black);
scrlArea = new QScrollArea(this);
scrlArea->setAutoFillBackground(true);
scrlArea->setPalette(pal);
scrlArea->setWidget(gol);
layout->addWidget(scrlArea);
setLayout(layout);
}
And I've left the paintEvent as it was. It was, ultimately, a size problem, as AlexanderVX said.