how do I set QScrollArea in my QWidget class constructor?

[Fagot]

Hello! I am new in QT.
I have items in QGridLayout created in the widget, I also need to put a QScrollArea across the height of my window there, but it is created in the upper left corner if I use this code, without scrollArea->setWidget(this);:

Widget::Widget(QWidget *parent)
    : QWidget(parent)
    , ui(new Ui::Widget)
{
    ui->setupUi(this);
    QGridLayout *grid = new QGridLayout(this);
    grid->setSpacing(2);
    QList<QString> values({ "1", "2", "3", "4"});
    int pos = 0;
    for (int i=0; i<2; i++) {
        for (int j=0; j<2; j++) {

            QPushButton *btn = new QPushButton(values[pos], this);
            btn->setFixedSize(40, 40);
            grid->addWidget(btn, i, j);
            pos++;
        }
    }
    setLayout(grid);
    QScrollArea *scrollArea = new QScrollArea(this);
    scrollArea->setWidgetResizable(true);
     //scrollArea->setWidget(this);
    scrollArea->setVerticalScrollBarPolicy(Qt::ScrollBarAlwaysOn);
}

I will have this :

If I write scrollArea->setWidget(this); then my window just won't open.
How I can resolve this problem?

[mpergand]

@Fagot said in how do I set QScrollArea in my QWidget class constructor?:

If I write scrollArea->setWidget(this); then my window just won't open.

Hi,
You have to create another widget,
an easy way would be to inherit from QScrollArea directly:

Widget(QWidget *parent) : QScrollArea(parent)
{
    setWidgetResizable(true);
    QGridLayout *grid = new QGridLayout;
    grid->setSpacing(10);
    QWidget* w=new QWidget;
    w->setLayout(grid);
    setWidget(w);

    for (int i=0; i<20; i++) {
        for (int j=0; j<2; j++) {
            QPushButton *btn = new QPushButton(QString("%1-%2").arg(i).arg((j)));
            btn->setFixedSize(80, 40);
            grid->addWidget(btn, i, j);
        }
    }
}

I get rid of setupUi() because I think it does nothing ;)

[Fagot]

@mpergand Thank You so much! You saved me a lot of time :))))