Communication between MainWindow and a dialog

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Hello again,

I have a main window that opens a dialog when a button is pressed.
When this happens it sends an instance of a class to the dialog for processing like so...

void on_push_0_clicked()
    {
    KeyDialog dialog(this); //Create dialog
    dialog.setKey(zero); //use setKey function of dialog
    dialog.exec(); //Show dialog
    }

void on_push_0_clicked()
    {
    KeyDialog dialog(this); //Create dialog
    dialog.setKey(zero); //use setKey function of dialog
    dialog.exec(); //Show dialog
    }

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(Michiel helped me with that one)

Now I want to send the processed instance back to the main window.

void KeyDialog::on_buttonBox_accepted()
 {
 //Copy key for safety
 Key::Key K2 = K1; //K1 is a global instance that is processed earlier in the form
//add new data from form
//changes vars in K2
mainWin.resetKey(K2);  //sends K2 back to mainwindow
}

void KeyDialog::on_buttonBox_accepted()
 {
 //Copy key for safety
 Key::Key K2 = K1; //K1 is a global instance that is processed earlier in the form
//add new data from form
//changes vars in K2
mainWin.resetKey(K2);  //sends K2 back to mainwindow
}

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But I guess my dialog has no knowledge of MainWindow because it says it hasn't been declared. How do I go about accesing this member function of MainWindow?

Thank you all very much for your help,
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