I have a list of todo elements managed by:

@Riverpod(keepAlive: true)
class TodosNotifier extends _$TodosNotifier {
  @override
  List<Todo> build() {
    return [.....some elements here.....];
  }

  void addTodo(Map<String, Object?> todo) {
    Todo todo = Todo.fromJson(todo);
    state = [...state, todo];
  }

  ...other methods here that change the state for different reasons...
}

and I have another Notifier which is meant to change its value only when the size of the TodosNotifier list changes (via addTodo(...)).

@Riverpod(keepAlive: true)
class TodosLengthNotifier extends _$TodosLengthNotifier {

  @override
  int build() => 0;

  void update() {
    // it never gets called here
    List<Todo> todos = ref.watch(todosNotifierProvider);
    if (state != todos.length) {
      state = todos.length;
    }
  }

}

The problem is that the method TodosLengthNotifier.update() never gets called every time I add a new “todo” element with TodosNotifier.addTodo(). How can I fix that?