Flutter依赖注入使用指南

1. 手动依赖注入

最简单的方式，通过构造函数传递依赖：

Dart 复制代码

class ApiService {
  Future<String> fetchData() async {
    // API 调用
    return 'Data';
  }
}

class UserRepository {
  final ApiService apiService;
  
  UserRepository(this.apiService);
  
  Future<String> getUserData() {
    return apiService.fetchData();
  }
}

class MyWidget extends StatelessWidget {
  final UserRepository userRepository;
  
  MyWidget({required this.userRepository});
  
  @override
  Widget build(BuildContext context) {
    return Text('User: ${userRepository.getUserData()}');
  }
}

// 使用
void main() {
  final apiService = ApiService();
  final userRepository = UserRepository(apiService);
  runApp(MyApp(userRepository: userRepository));
}

2. 使用 Provider 包

最流行的 Flutter 状态管理和依赖注入方案：

Dart 复制代码

dependencies:
  provider: ^6.0.5

Dart 复制代码

import 'package:provider/provider.dart';

// 定义服务类
class CounterService {
  int _count = 0;
  int get count => _count;
  
  void increment() {
    _count++;
  }
}

void main() {
  runApp(
    MultiProvider(
      providers: [
        Provider<CounterService>(create: (_) => CounterService()),
        // 可以添加更多 provider
      ],
      child: MyApp(),
    ),
  );
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: MyHomePage(),
    );
  }
}

class MyHomePage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    final counterService = Provider.of<CounterService>(context);
    
    return Scaffold(
      body: Center(
        child: Text('Count: ${counterService.count}'),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: () {
          counterService.increment();
        },
        child: Icon(Icons.add),
      ),
    );
  }
}

依赖注入是将对象的创建和使用分离，使代码更加灵活、可测试和可维护