I have a Main Window were i create a custom widget and set it as the Central Widget:

MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
{
    mMineField = new MineField(4, 4, 3, this);
    setCentralWidget(mMineField);
}

The MineField creates depending of which width and height is supplied a count of Cells to display.

#include <QVector>
#include <QWidget>

#include "cell.h"

class MineField : public QWidget
{
    Q_OBJECT
public:
    explicit MineField(int width,
                       int height,
                       int countOfBombs,
                       QWidget *parent = nullptr);

private:
    QVector<Cell *> createCells(int width, int height, int countOfBombs);

    int mWidth;
    int mHeight;
    QVector<Cell *> mCells;
};

I try to create the Cells and add the to a grid layout like this:

#include "minefield.h"

#include "cell.h"

#include <QDebug>
#include <QGridLayout>

#include <random>

MineField::MineField(int width,
                     int height,
                     int countOfBombs,
                     QWidget *parent)
    :QWidget{ parent },
      mWidth{ width},
      mHeight{ height },
      mCells{ createCells(width, height, countOfBombs) }
{
    auto layout = new QGridLayout;

    for(int i = 0; i < mCells.size(); ++i) {
        auto row = static_cast<int>(i %  mWidth);
        auto column = static_cast<int>(i /  mWidth);

        qDebug() << "Column = " << column << " Row = " << row;

        layout->addWidget(mCells[i], row, column);
    }

    setLayout(layout);
}

QVector<Cell *> MineField::createCells(
        int width, int height, int countOfBombs)
{
    QVector<Cell *> cells;
    auto size = static_cast<int>(width * height);
    cells.reserve(size);

    for(auto i = 0; i < size; ++i) {
        if(i < countOfBombs) {
            cells.push_back(new Cell(Cell::State::mine, this));
        }
        else {
            cells.push_back(new Cell(Cell::State::empty, this));
        }
    }
    return cells;
}

However i don't see anything displayed in the window. Is there an Issue in how i create the widgets dynamically?

Edit:

It looks like the Cells are at the correct position. Just the image of them is not displayed. I already tested that Cell paints itself directly in a QMainWindow. Then Why it does not work in the Layout?.

The Cell is also derrived from QWidget and paints like this:

void Cell::paintEvent(QPaintEvent *event)
{
    Q_UNUSED(event)
    QPainter painter{ this };  
    painter.drawImage(geometry(), displayImage(mDisplayType));
}