ScrollNotificationObserver class

Notifies its listeners when a descendant scrolls.

To add a listener to a ScrollNotificationObserver ancestor:

ScrollNotificationObserver.of(context).addListener(_listener);

To remove the listener from a ScrollNotificationObserver ancestor:

ScrollNotificationObserver.of(context).removeListener(_listener);

Stateful widgets that share an ancestor ScrollNotificationObserver typically add a listener in State.didChangeDependencies (removing the old one if necessary) and remove the listener in their State.dispose method.

Any function with the ScrollNotificationCallback signature can act as a listener:

// (e.g. in a stateful widget)
void _listener(ScrollNotification notification) {
  // Do something, maybe setState()
}

This widget is similar to NotificationListener. It supports a listener list instead of just a single listener and its listeners run unconditionally, they do not require a gating boolean return value.