...connect(nextPhotoAction, SIGNAL(triggered()), SLOT(nextPhoto()));...void MainWindow::nextPhoto(){ emit dbCreate::writeData();}
void dbCreate::writeData(){ чего-то делает}
C++ (Qt)dbCreate *obj;connect(nextPhotoAction, SIGNAL(triggered()), obj, SLOT(writeData()));
viewChecker = new dbViewer;connect(nextPhotoAction, SIGNAL(triggered()), viewChecker, SLOT(writeDB()));
db = new dbCreate;connect(а тут чего?, SIGNAL(triggered()), db, SLOT(writeData()));
C++ (Qt)viewChecker = new dbViewer;connect(nextPhotoAction, SIGNAL(triggered()), viewChecker, SIGNAL(mySignal()));...db = new dbCreate;connect(this, SIGNAL(mySignal()), db, SLOT(writeData()));