I'm not completely sure I understand the use case, but I'll try and answer as I understand it. If this is supposed to be updating in real time, I would think your best bet would be to create a signal/slot between the main window and the dialog. Whenever the text in the edit box on the Main Window changes, it passes the new string to the dialog which can update it's own copy of the string. If it's just a one way communication this should work fine. If you need two way (such as editing in the main window updates both, editing in the dialog updates both) you would need to be a bit more careful not to create a loop with the signals.