QDataWidgetMapper ImmediateSubmit policy

void ImmediateDataWidgetMapper::addMapping(QWidget *widget, int section, QByteArray propertyName) {
  // since QDataWidgetMapper makes its widget map private we have no way of
  // getting all of the widgets registered with this mapper
  // we also do not want to hook up a widget that's already mapped
  if (widgetList.contains(widget)) return;
  widgetList.append(widget);
  QDataWidgetMapper::addMapping(widget, section, propertyName);
  // we use the QDataWidgetMapper to tell us what property we should listen to for changes
  // all widgets have several properties, but most have a "primary" property with which
  // the user interacts, i.e. "checked" for QCheckBox
  propertyName = this->mappedPropertyName(widget);
  // we use the widget's meta object in order to get us a signal that we can listen to
  // so we know when this property changes
  auto widgetMetaObject = widget->metaObject();
  auto property = widgetMetaObject->property(widgetMetaObject->indexOfProperty(propertyName));
  auto metaObject = this->metaObject();
  QMetaObject::connect(widget, property.notifySignalIndex(), this, metaObject->indexOfSlot("widgetChanged()"));
}