Create QLabel besides the constructor - c++

Question

I have a vector of labels, declared in the MainWindow class:
QVector<QPointer<QLabel>> labels;
And a function:
void MainWindow::testFunc()
{
for(int i = 0; i < 5; ++i) {
labels.push_back(QPointer<QLabel>(new QLabel(this)));
labels.back()->setGeometry(QRect(50 * i, 0, 50, 50));
labels.back()->setText("test");
}
}
I call this function in the class constuctor and everything is fine:
MainWindow::MainWindow(QWidget *parent)
: QMainWindow(parent)
, ui(new Ui::MainWindow)
{
ui->setupUi(this);
testFunc();
}
Then I added a button and a connecting:
MainWindow::MainWindow(QWidget *parent)
: QMainWindow(parent)
, ui(new Ui::MainWindow)
{
ui->setupUi(this);
connect(ui->pushButton, &QPushButton::clicked, this, &MainWindow::testFunc);
}
And after clicking the labels aren't shown. I checked via debugger and in the both ways the labels are created and constructors for them are executed. Also I tried simple pointers, QTimer::singleShot() and QPointer<QLabel> without QVector - the result is the same.
Why the second way does't work? Why I can add a QLabel only in the constuctor?

Answer 1

QMainWindow alwayd should have a centralWidget that contains other chilrens. when using forms, centralWidget is automaticly created. you may manage labels in a horizontal layout and then add them to the centralWidget:
QPointer<QHBoxLayout> hBoxLayout (new QHBoxLayout);
for(int i = 0; i < 5; ++i) {
labels.push_back(QPointer<QLabel>(new QLabel));
labels.back()->setGeometry(QRect(50 * i, 0, 50, 50));
labels.back()->setText("test");
hBoxLayout->addWidget(labels.back().data());
}
ui->centralwidget->setLayout(hBoxLayout);