Access MainWindow class members from another class - c++

Question

I googled a lot before writing here. I found a couple of posts but I couldn't quite get them. So I'm starting a new post.
I am developing a simple UI. There is this main class (see below), which is a main dialogue box which is shown when the app is started.
class MainWindow : public QMainWindow
There are few buttons on the MainWindow dialogue box, when I click a button, it hides the MainWindow and opens another QDialog box. This dialogue box is of the class as shown below
class libinsert : public QDialog
I create the libinsert object this way:
void MainWindow::on_pushButton_clicked()
{
this->hide();
libinsert lib; // I create libinsert object this way
lib.setModal(true);
lib.exec();
}
This is libinsert.cpp:
libinsert::libinsert(QWidget *parent) :
QDialog(parent),
ui(new Ui::libinsert)
{
ui->setupUi(this);
}
When the libinsert dialogue box is open, I need to access a socket variable which is a member of class MainWindow. How do I achieve this ?
My main app looks like this:
{
QApplication a(argc, argv);
MainWindow w(sock);
w.show();
return a.exec();
};
Alternatively: in general how are multiple dialogue boxes built, as parent-child relation?

Answer 1

libinsert will not be a child of MainWindow. QDialog-based windows are always top-level windows, regardless of what you pass as their parent when you construct them.
If there will only ever exist a single instance (per process) of MainWindow at any given time, you can give MainWindow a static function which returns a pointer to the window:
class MainWindow : public QMainWindow
{
public:
MainWindow()
{
theWindow = this;
}
virtual ~MainWindow()
{
theWindow = nullptr;
}
static get()
{
return theWindow;
}
static MainWindow *theWindow;
}
MainWindow *MainWindow::theWindow = nullptr;
Your dialogs can then access the main window's members thusly:
MainWindow::get()->someMemberFunction();
A more robust approach is to have libinsert store a pointer to the main window when it is created:
class MainWindow;
class libinsert : public QDialog
{
public:
libinsert(MainWindow *mw)
: mainWindow(mw)
{ ... }
MainWindow *getMainWindow()
{
return mainWindow;
}
MainWindow *mainWindow;
}
When MainWindow creates the dialog, it passes a pointer to itself to the constructor:
void MainWindow::createDialog()
{
libinsert *dialog = new libinsert(this):
}
This approach will work even if there are multiple instances of MainWindow active at the same time.