how do I call primary window using pushbutton c++ - c++

Question

I'm trying to create a C++ Widget Application in QT with multiple windows where you can return to the mainwindow by clicking a Pushbutton.
I'm a complete noobie so I try to follow YouTube tutorial and for opening windows by pushbuttons I watched this one (minute 8:00): https://youtu.be/tP70B-pdTH0
It works when opening secondary windows from the main one but if I try to do the same from a secondary windows to the mainwindow it doesn't. It appears an error "cannot initialize object parameter of type 'Widget' with an expression of type 'MainWindow'"
in the source file I wrote:
void Crediti::on_pushButton_clicked()
{
close();
mainwindow = new MainWindow(this);
mainwindow->show();
}
mainwindow->show(); is the incriminated part
I also included mainwindow in the header of the secondary window and specified the class
MainWindow *mainwindow
in the header so It recognizes mainwindow initially in the source.
I'm doubting if doing this thing is possible at all, and if not so how can I make a pushbutton that, when clicked, can redirect me to the mainwindow?
Please I need this for a school application, thanks

Answer 1

So here you're creating a new main window each time you click on the button. From your description that's not the behaviour you want. I understand you have an application with a main window and other secondary windows and want to bring up the main window when clicking on the button, assuming the main window still exists somewhere and hasn't been deleted.
What I would try is to find the main window when hitting the push button and show / raise it, something along the line of:
#include <QApplication>
#include "MainWindow.h" // Adapt that one to you main window header
// ... some code of your secondary window
void SecondaryWindow::on_pushButton_clicked()
{
for(auto widget : QApplication::topLevelWidgets())
{
// This will return a nullptr if the widget is not the main window
auto mainWindow = dynamic_cast<MainWindow*>(widget);
// skip if not the main window
if(!mainWindow)
continue;
// Show it if hidden
if(mainWindow->isHidden())
mainWindow->show();
// raise it, as in bring it forward, over all other windows
mainWindow->raise();
}
// eventually close the current window if that's what you want
close();
// if you close it and don't need it any more you might also want to delete it
deleteLater();
}
Note that this function won't do anything if the main window has been deleted in the meantime, which might be the case if you closed it and the Qt::WA_DeleteOnClose attribute is set.
Hope that helps.