```dart
StreamSubscription<SubscriptionEvent<Post>>? stream;

void listenChanges() {
  stream = Amplify.DataStore.observe(Post.classType).listen(
    (event) {
      print('Received event of type ' + event.eventType.toString());
      print('Received post ' + event.item.toString());
    },
  );
}

void stopListeningChanges() {
  stream?.cancel();
}
```