Qt QFrame becomes separate window

Question

I'm constructing UI in QT programatically. The problem is when making a Qframe , setting into a layout and adding the layout to my main window, the frame becomes a window of it's own. I've searched around but I can't seem to get it to become a frame within my main window.

    MainWindow::MainWindow()
    {

        QWidget::showMaximized();
        frame = new QFrame();
        layout = new QHBoxLayout();
        button = new QPushButton("Push");

        layout->addWidget(frame);
        frame->show();
        this->setLayout(layout);

        Setstyles();
    }

Answer 1

The problem is, QFrame inherits from QWidget, and if it has no parent, it is going to create a window.

From QWidget:details section :

Every widget's constructor accepts one or two standard arguments:

1. QWidget *parent = 0 is the parent of the new widget. If it is 0 (the default), the new widget will be a window. If not, it will be a child of parent, and be constrained by parent's geometry (unless you specify Qt::Window as window flag).

To fix your specific case, create the QFrame object with the parent :

frame = new QFrame(this);

Answer 2

You can not set layout of a QMainWindow (or simple subclass), you can only set it's central widget. I assume your MainWindow is a subclass of QMainWindow . But you can of course set layout to that central widget, so you can do this:

MainWindow::MainWindow() // parent will be nullptr, so this will be a window
{
    showMaximized();

    // create and set central widget
    QWidget *cw = new QWidget();
    setCentralWidget(cw); // will set cw's parent
    // Note: there's no need to make cw a member variable, because
    // MainWindow::centralWidget() gives direct access to it

    frame = new QFrame();
    layout = new QHBoxLayout();
    button = new QPushButton("Push"); // this is not used at all? why is it here?

    layout->addWidget(frame);
    //frame->show(); // not needed, child widgets are shown automatically
    cw->setLayout(layout); // will set parent of all items in the layout

    Setstyles();
}