Passing data from a QDialog to a QMainWindow using signal/slots

[stampede]

You create a new dialog in main window's constructor and never exec it, it is useless.
Remove it from the constructor and connect to instances created in on_Open_clicked() slot:

void MainWindow::on_Open_clicked()
{
    Dialog *dialog = new Dialog (this); // remember to set parent !
    dialog->setModal(true);
    connect(dialog, SIGNAL(validate(QString)), this, SLOT(validate(QString)));
    dialog->exec();
 
}

void MainWindow::on_Open_clicked()
{
    Dialog *dialog = new Dialog (this); // remember to set parent !
    dialog->setModal(true);
    connect(dialog, SIGNAL(validate(QString)), this, SLOT(validate(QString)));
    dialog->exec();
 
}

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[anda_skoa]

QDialog::exec() always sets modality to true, so no need to do that explicitly

Cheers,
_