How to show a QMainWindow inside a QDialog

Question

I am trying to show a QMainWindow inside a QDialog but the former does not appear.

I have subclassed QDialog, let's call it myDialog

A small example:

myDialog(QWidget *p_parent) : QDialog(p_parent)
{
    QGridLayout *p_dialogLayout = new QGridLayout(this);

    QMainWindow *p_MainWindow = new QMainWindow(this);
    QLabel *p_label = new QLabel(this);
    p_MainWindow->setCentralWidget(p_label);

    QPushButton *p_cancel = new QPushButton("Cancel", this);

    p_dialogLayout ->addWidget(p_MainWindow, 0, 0);
    p_dialogLayout ->addWidget(p_cancel, 1, 0);
}

If I execute the dialog, I only see the button, not the embeded QMainWindow. If i force to show the qmainwindow, the mainwindow is shown in another window.

Answer 1

Use QLayout::setMenuBar to add a toolbar to your dialog.

#include <QtWidgets>

class Dialog : public QDialog
{
    Q_OBJECT
public:
    Dialog(QWidget *parent = nullptr) : QDialog(parent)
    {
        resize(600, 400);
        setLayout(new QHBoxLayout);
        QToolBar *toolbar = new QToolBar;
        toolbar->addAction("Action one");
        toolbar->addAction("Action two");
        layout()->setMenuBar(toolbar);

        layout()->addWidget(new QLabel("Label one"));
        layout()->addWidget(new QLabel("Label two"));
    }
};

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    Dialog w;
    w.show();

    return a.exec();
}

#include "main.moc"

Answer 2

I don't think this is supported by the Qt framework, according to their documentation from here , it's intended to be used only once in an application.

My suggestion would be to take all your MainWindow implementation in a separate form (inheriting QWidget ), and just add that form to your MainWindow in the constructor using something like p_MainWindow->setCentralWidget(p_YourNewForm);

Answer 3

I have been able to do it.

The trick is to construct the QMainWindow without a parent, and then apply the .setParent

Here is how:

myDialog(QWidget *p_parent) : QDialog(p_parent)
{
    QGridLayout *p_dialogLayout = new QGridLayout(this); 

    QMainWindow *p_MainWindow = new QMainWindow(); //Without a parent
    QLabel *p_label = new QLabel(this);
    p_MainWindow->setCentralWidget(p_label);

    QPushButton *p_cancel = new QPushButton("Cancel", this);

    p_dialogLayout ->addWidget(p_MainWindow, 0, 0);
    p_dialogLayout ->addWidget(p_cancel, 1, 0);

    p_MainWindow->setParent(this); //Set the parent, to delete the MainWindow when the dialog is deleted.
}