Interaction between QMainWindow class and QDialogue class - c++

Question

I am developing a GUI app. I have a main window(QMainWindow) which pops up when the app is executed.
{
QApplication a(argc, argv);
MainWindow w;
w.show();
return a.exec();
}
This window has some buttons. When I click a button here, another window which is of QDialog is popped up. The logic of the button is
void MainWindow::on_InsertButton_pressed()
{
libinsert lib ;
lib.setModal(false);
lib.exec();
}
Question: I have a socket in the QMainWindow class, whenever I receive a message there I need to send it to the QDialogue window and display it in a QLineEdit. With the above logic, even after I set QDialogue to nonmodal, I am not able to interact with the QMainWindow when the QDialogue window is open. I tried lib.show() instead of lib.exec(), but with this, when I click the button the QMainWindow class the QDialogue window does not pop up.
Please advice me what is the best method to communicate from the background window the the foreground window?

Answer 1

Your code can looks like
void MainWindow::on_InsertButton_pressed()
{
libinsert lib ;
connect( this, SIGNAL( messageReceived( QString ), &lib, SLOT( letsChangeLineEdit( QString ) ) ) );
lib.setModal(false);
lib.exec();
}
Of course you should implement your signal and slot. QString in signal slot arguments is target string to show in dialog.
Hope that will clear for you.

Answer 2

In your MainWindow::on_InsertButton_pressed()slot you are creating a local variable libinsert lib which gets destroyed when it gets out of scope, i.e. when the slot execution finishes. If you use lib.exec() the execution waits for the dialog execution to return so you see the dialog, but can't interact with the main window until you close it. When you use lib.show(), your dialog is shown, execution continues and exits the slot right away, at which point the lib gets destroyed and you don't see it any more (depending on your configuration this may be fast enough that it looks like it newer gets shown in the first place).
One solution is to have a pointer to your dialog as a member of MainWindow class (add libinsert* lib; in MainWindow.h), and initialize it in your Mainwindow constructor like this:
`MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{
ui->setupUi(this);
lib = new libinsert(this);
lib->setModal(false);
}`
Then in MainWindow::on_InsertButton_pressed() you only need to call QWidget::show() method, i.e. like this:
void MainWindow::on_InsertButton_pressed()
{
lib->show();
}
Now, if what you are trying to achieve is to have a dialog pop-up every time the message is received , and display the message, first you will need to have a public method(or slot) in your libinsert class which updates the text in your QLineEdit, for example
void libinsert::onMessageReceived(QString message)
{
// Update the text and show the dialog to avoid having to call show()
// explicitly from MainWindow.
ui->lineEdit->setText(message);
show();
}
and then either call this method directly, when you receive the message, with:
lib->onMessageReceived(message);
or connect a signal, emitted when message is received, to it with something like this (in MainWindow constructor):
connect( this, SIGNAL( messageReceived( QString ), &lib, SLOT( onMessageReceived( QString ) ) ) );