Is there a maximum number of QLabels in a screen?

TomNow99

Hello,
My code:

    int a=90;
    label.resize(a);

    for(int i=0;i<a;i++)
        label[i].resize(a);

    for(int i=0;i<a;i++)
    {
        for(int j=0;j<a;j++)
        {
            label[i][j]=new QLabel(this);

            label[i][j]->setGeometry(i*5,j*5,5,5);
            label[i][j]->setStyleSheet("QLabel {background:red; border: 1px solid black}");
        }
    }

( label is QVector with QLabels ).

When I set a=80 everything is ok. When I change it to 81 my app is crashed.

When I use QGridLayout and add to it QLabels result is the same - 80 ( ok ), 81 (not ok ).

So maximum number of QLabels is between 6400 ( 80^2) and 6561 (81^2)?

EDIT I think my pc can display many QLabels :)

J.Hilk

@TomNow99

Works perfectly fine for me.

int main (int argc, char *argv[])
{

    QApplication app(argc, argv);

    QVector<QVector<QLabel*> > label;

    int a=90;
    label.resize(a);

    for(int i=0;i<a;i++)
        label[i].resize(a);

    for(int i=0;i<a;i++)
    {
        for(int j=0;j<a;j++)
        {
            label[i][j]=new QLabel(nullptr);

            label[i][j]->setGeometry(i*5,j*5,5,5);
            label[i][j]->setStyleSheet("QLabel {background:red; border: 1px solid black}");
        }
    }
    return 0;
}

TomNow99

@J-Hilk When I run your code it works, but doesn't see any QLabels. You don't set parent.

J.Hilk

@TomNow99

int main (int argc, char *argv[])
{

    QApplication app(argc, argv);

    QVector<QVector<QLabel*> > label;

    int a=90;
    label.resize(a);

    for(int i=0;i<a;i++)
        label[i].resize(a);

    QWidget w;
    w.resize(a * 5, a* 5);

    for(int i=0;i<a;i++)
    {
        qDebug() << i << "of" << a;
        for(int j=0;j<a;j++)
        {
            label[i][j]=new QLabel(&w);

            label[i][j]->setGeometry(i*5,j*5,5,5);
            label[i][j]->setStyleSheet(QStringLiteral("QLabel {background:red; border: 1px solid black}"));
        }
    }

    w.show();

    qDebug() << "Now showing";

    return app.exec();
}

TomNow99

@J-Hilk Still crashed. So this is my pc problem. Thank you for help :)

J.Hilk

@TomNow99
I ran it in release, because in debug it took quite literally forever to create that many QLabels

only 70mb ram, is consumed so I doubt thats the problem:

that said, if your only objective is to create such a grid, you can do that easily with overwriting paint event on a QWidget class:

class SomeClass : public QWidget
{
    Q_OBJECT

public:
    explicit SomeClass(int a, QWidget *parent = nullptr)
        : QWidget(parent), m_a(a)
    {
        resize(5 * a, 5 * a);
    }
    

protected:
    int m_a;
    virtual void paintEvent(QPaintEvent *event) override{
        QPainter p(this);

        p.fillRect(rect(), Qt::red);
        p.setBrush(QBrush(Qt::black));
        for(int i (0); i < m_a; i++) {
            //Vertical
            p.drawLine(5 * i, 0, 5 * i, height());

            //Horizontal
            p.drawLine(0, 5 * i, width(), 5 * i);
        }
    }
};

int main (int argc, char *argv[])
{

    QApplication app(argc, argv);

    SomeClass s(90);
    s.show();

    return app.exec();
}

JonB

@TomNow99
Maximum number of widgets should only be limited by memory. However, performance & resources will be hit. You simply should not create 6.5K labels, whether it works or not. Next you'll be wanting to do a connect() on each one, with 6.5K signal/slots :) @J-Hilk has shown a way of creating a grid just via painting, you should be looking for a solution like that or similar.

This, by the way, is also the reason why one-man crusaders like @VRonin are on a mission to rid the world of QTableWidget::setCellWidget() --- can create too many individual widgets when used in a table, where a QStyledItemDelegate can do the job via drawing instead of creating actual widgets.