QMainWindow or QDialog show() - before displaying, the window area is painted white

[VVS]

I solved this problem.

class Dialog1 : public QDialog
{
    Q_OBJECT
 
public:
    explicit Dialog1(QWidget *parent = nullptr);
    ~Dialog1();
 
private:
    Ui::Dialog1 *ui;
protected:
    bool event(QEvent*e);
};

class Dialog1 : public QDialog
{
    Q_OBJECT

public:
    explicit Dialog1(QWidget *parent = nullptr);
    ~Dialog1();

private:
    Ui::Dialog1 *ui;
protected:
    bool event(QEvent*e);
};

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Dialog1::Dialog1(QWidget *parent) :
    QDialog(parent),ui(new Ui::Dialog1)
{
    ui->setupUi(this);
 
    setWindowFlags(Qt::Window);
    setWindowOpacity(0);
}
 
bool Dialog1::event(QEvent*e)
{
    if(e->type()==QEvent::WindowActivate)
    {
        QTimer::singleShot(0,NULL,[this](){this->setWindowOpacity(1);});
        return true;
    }
    if(e->type()==QEvent::Hide)
    {
        setWindowOpacity(0);
        return true;
    }
    return QDialog::event(e);
}

Dialog1::Dialog1(QWidget *parent) :
    QDialog(parent),ui(new Ui::Dialog1)
{
    ui->setupUi(this);

    setWindowFlags(Qt::Window);
    setWindowOpacity(0);
}

bool Dialog1::event(QEvent*e)
{
    if(e->type()==QEvent::WindowActivate)
    {
        QTimer::singleShot(0,NULL,[this](){this->setWindowOpacity(1);});
        return true;
    }
    if(e->type()==QEvent::Hide)
    {
        setWindowOpacity(0);
        return true;
    }
    return QDialog::event(e);
}

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This is not a Qt problem, this is a Windows problem. I looked at my WPF and Windows Forms projects and saw that they have this problem. You can also see it by running Windows Explorer or Windows Task Manager. Another question is whether this is considered a problem. I think so, Yes. This flickering hits my eyes