AppFlowy/app_flowy/packages/flowy_infra/lib/notifier.dart

import 'package:flutter/material.dart';

class PublishNotifier<T> extends ChangeNotifier {
  T? _value;

  set value(T newValue) {
    if (_value != newValue) {
      _value = newValue;
      notifyListeners();
    }
  }

  T? get currentValue => _value;

  void addPublishListener(void Function(T) callback) {
    super.addListener(
      () {
        if (_value != null) {
          callback(_value!);
        }
      },
    );
  }
}