dependencies:
  hive_flutter: ^1.1.0 //add this line

dev_dependencies:
  build_runner: ^2.2.1 //add this line
  hive_generator: ^1.1.3 //add this line

.
├── lib                  
    ├── core
        └── service
            ├── cache
                ├── base_cache_manager.dart
                └── cache_enums.dart   
    ├── model
        ├── todo_model.dart
        └── todo_model.g.dart
    └── product
        └── todo
            ├── todo_service.dart
            └── todo_view.dart
└── main.dart

  await Hive.initFlutter();

Future<void> boxInit() async {
  await Hive.openBox(boxName);
}

Future<void> addItemWithAutoIncrementKey(T item) async {
  await _box!.add(item);
}

Future<void> addItemWithCustomKey(dynamic key, T item) async {
  await _box!.put(key, item);
}

T? getItem(dynamic key) {
  return _box!.get(key);
}

Future<void> removeItem(dynamic key) async {
  await _box!.delete(key);
}

Future<void> clearBox() async {
  await _box!.clear();
}

Future<void> closeBox() async {
  await _box!.close();
}

import 'package:hive_flutter/adapters.dart';
part 'todo_model.g.dart';

@HiveType(typeId: 1)
class Todo {
  @HiveField(0)
  int? userId;
  @HiveField(1)
  int? id;
  @HiveField(2)
  String? title;
  @HiveField(3)
  bool? completed;

  Todo({this.userId, this.id, this.title, this.completed});

  Todo.fromJson(Map<String, dynamic> json) {...}
  Map<String, dynamic> toJson() {...}
}

flutter pub run build_runner build

final BaseCacheManager<Todo> _todoCacheManager = BaseCacheManager<Todo>(boxName: CacheBoxNames.todo);
Future<void> serviceInit() async {
  await _todoCacheManager.boxInit();
}

await _todoCacheManager.boxInit();
_todoCacheManager.getItemList();
await _todoCacheManager.addItemList(items);
await _todoCacheManager.clearBox();
...