dispatch method

void dispatch (BuildContext target)

Start bubbling this notification at the given build context.

The notification will be delivered to any NotificationListener widgets with the appropriate type parameters that are ancestors of the given BuildContext.

Implementation 

void dispatch(BuildContext target) {
  assert(target != null); // Only call dispatch if the widget's State is still mounted.
  target.visitAncestorElements(visitAncestor);
}