Widget 体系与 State 管理

Widget 类型

State 管理基础

class MyWidget extends StatefulWidget {
  @override
  State<MyWidget> createState() => _MyWidgetState();
}

class _MyWidgetState extends State<MyWidget> {
  int _counter = 0;

  void _increment() {
    setState(() { _counter++; }); // 触发重建
  }
}

BuildContext

每个 Widget 的 build() 方法接收 BuildContext。Context 包含：

• 当前 widget 在 widget 树中的位置
• 访问 Theme.of(context)、MediaQuery.of(context)
• 访问祖先 widget 提供的 InheritedWidget

布局约束

核心规则

"Constraints go down. Sizes go up. Parent sets position."

父 widget 向下传递约束；子 widget 向上报告尺寸；父 widget 决定子 widget 的位置。

BoxConstraints

常用布局 Widget

常见布局错误

// ❌ Expanded 在 Stack 中无效 → 用 Positioned 或 Align
// ❌ 在 unbounded 约束中 Expanded 无效 → 用 Slivers

// ✅ ConstrainedBox 在 Loose 约束内
ConstrainedBox(
  constraints: BoxConstraints(minWidth: 100, maxWidth: 200),
  child: Text('Hello'),
)

详细参考：layout-constraints.md

Material 3 迁移

核心开关

MaterialApp(
  theme: ThemeData(useMaterial3: true),
);

关键变化

种子色

ColorScheme.fromSeed(seedColor: Colors.blue)

详细参考：material-3.md

动画系统

Hero 动画

// 页面 A 和 B
Hero(
  tag: 'photo',
  child: Image.asset('photo.jpg'),
)

Staggered 动画

// 一个控制器驱动多个 Interval 动画
Animation<double> get _opacity => Tween(begin: 0.0, end: 1.0).animate(
  CurvedAnimation(parent: _controller, curve: Interval(0.0, 0.5)),
);
Animation<double> get _scale => Tween(begin: 0.0, end: 1.0).animate(
  CurvedAnimation(parent: _controller, curve: Interval(0.5, 1.0)),
);

详细参考：hero-animations.md | staggered-animations.md

State 管理方案对比

Provider（入门级）

// ChangeNotifier
class CounterModel extends ChangeNotifier {
  int _count = 0;
  int get count => _count;
  void increment() { _count++; notifyListeners(); }
}

// 注册
runApp(ChangeNotifierProvider(
  create: (_) => CounterModel(),
  child: MyApp(),
));

// 重建 UI
Consumer<CounterModel>(
  builder: (context, model, child) => Text('${model.count}'),
);

// 读取（不重建）
final count = context.read<CounterModel>().count;

Riverpod（生产推荐）

// 纯 Dart，无 context 依赖
final counterProvider = StateNotifierProvider<CounterNotifier, int>((ref) {
  return CounterNotifier();
});

class CounterNotifier extends StateNotifier<int> {
  CounterNotifier() : super(0);
  void increment() => state++;
}

// 使用
Widget build(BuildContext context, WidgetRef ref) {
  final count = ref.watch(counterProvider);
  return Text('$count');
}

// ref.watch vs ref.read
// watch: 重建 UI（监听变化）
// read: 不重建，仅读取当前值（事件处理中常用）

// 强制刷新 Provider
ref.invalidate(counterProvider);  // 重置状态，重新执行 Provider 回调
// 或者基于现有状态刷新
ref.invalidate(myProvider);  // 下次访问时重新创建

// Family Provider（带参数）
final userProvider = Provider.family<User, String>((ref, id) {
  return User(id: id, name: 'User $id');
});
// 使用
final user = ref.watch(userProvider('abc'));

Provider 作用域

// ✅ 顶层 Provider：全局单例
final prefsProvider = Provider<SharedPreferences>((ref) {
  return SharedPreferences.getInstance() as SharedPreferences;
});

// ✅ 作用域 Provider：仅在子树内有效
ProviderScope(
  overrides: [counterProvider.overrideWith(() => MockCounter())],
  child: MyApp(),
);

// ✅ Child Provider：可读取父 Provider
final userProvider = Provider((ref) {
  final prefs = ref.watch(prefsProvider); // 依赖父 Provider
  return UserRepo(prefs: prefs);
});

BLoC（大型项目）

class CounterBloc extends Bloc<CounterEvent, int> {
  CounterBloc() : super(0) {
    on<Increment>((event, emit) => emit(state + 1));
  }
}

BlocBuilder<CounterBloc, int>(
  builder: (context, count) => Text('$count'),
)

方案选型

持久化存储

SharedPreferences（轻量配置）

final prefs = await SharedPreferences.getInstance();
await prefs.setString('username', 'yhong');
await prefs.setInt('counter', 42);
final name = prefs.getString('username') ?? '';
await prefs.remove('counter');

SQLite（结构化数据）

final db = await openDatabase('myapp.db', version: 1,
  onCreate: (db, version) async {
    await db.execute(
      'CREATE TABLE tasks(id INTEGER PRIMARY KEY, title TEXT)');
  });

await db.insert('tasks', {'title': 'Finish report'});
final maps = await db.query('tasks', where: 'id = ?', whereArgs: [1]);

// 批量事务
await db.transaction((txn) async {
  for (final task in tasks) await txn.insert('tasks', task);
});

Hive（高性能 KV）

Hive.registerAdapter(TaskAdapter());
final box = await Hive.openBox<Task>('tasks');
box.put('task1', Task(title: 'Hello'));
final task = box.get('task1');

网络请求

Dio（推荐）

final dio = Dio(BaseOptions(
  baseUrl: 'https://api.example.com',
  connectTimeout: Duration(seconds: 10),
  headers: {'Content-Type': 'application/json'},
));

// 全局拦截器：Token 自动附加
dio.interceptors.add(InterceptorsWrapper(
  onRequest: (options, handler) {
    final token = getToken(); // 从安全存储读取
    if (token != null) {
      options.headers['Authorization'] = 'Bearer $token';
    }
    handler.next(options);
  },
  onError: (error, handler) {
    // Token 过期自动刷新重试
    if (error.response?.statusCode == 401) {
      refreshToken().then((newToken) {
        // 重试原请求
        final opts = error.requestOptions;
        opts.headers['Authorization'] = 'Bearer $newToken';
        dio.fetch(opts).then(
          (r) => handler.resolve(r),
          (e) => handler.reject(e),
        );
      }).catchError((e) => handler.reject(error));
    } else {
      handler.next(error);
    }
  },
));

// GET / POST
final resp = await dio.get('/users', queryParameters: {'page': 1});
final resp = await dio.post('/users', data: {'name': 'yhong'});

统一响应体处理

// 常见后端响应格式：{ code, data, message }
class ApiResp<T> {
  final int code;
  final T? data;
  final String? message;

  bool get ok => code == 0;
}

// Dio 响应拦截器统一解析
dio.interceptors.add(InterceptorsWrapper(
  onResponse: (resp, handler) {
    final body = resp.data;
    if (body is Map && body.containsKey('code')) {
      if (body['code'] != 0) {
        // 业务错误，转为异常
        handler.reject(
          DioException(
            requestOptions: resp.requestOptions,
            error: body['message'] ?? 'Unknown error',
            type: DioExceptionType.badResponse,
          ),
        );
        return;
      }
      // 替换为 data 部分
      resp.data = body['data'];
    }
    handler.next(resp);
  },
));

// 使用时直接取 data
final List users = await dio.get('/users').then((r) => r.data);

错误处理

try {
  final resp = await dio.get('/users');
} on DioException catch (e) {
  switch (e.type) {
    case DioExceptionType.connectionTimeout:
      // 网络超时
    case DioExceptionType.badResponse:
      final statusCode = e.response?.statusCode;
      if (statusCode == 401) { /* 未授权 */ }
      if (statusCode == 403) { /* 禁止 */ }
      if (statusCode == 404) { /* 资源不存在 */ }
      if (statusCode != null && statusCode >= 500) { /* 服务器错误 */ }
    case DioExceptionType.cancel:
      // 请求被取消
    default:
      // 网络不可达等
  }
}

JSON 解析

@JsonSerializable()
class User {
  final String name;
  final int age;
  factory User.fromJson(Map<String, dynamic> json) => _$UserFromJson(json);
  Map<String, dynamic> toJson() => _$UserToJson(this);
}

性能优化

重建控制

// ✅ Selector 精确重建（替代 Consumer）
Selector<Model, String>(
  selector: (_, m) => m.title,
  builder: (_, title, __) => Text(title),
);

// ✅ const 构造
const Text('Hello');
const Padding(padding: EdgeInsets.all(16));

// ❌ build 中创建新对象
Widget build(BuildContext context) {
  return SomeWidget(items: List.generate(100, (i) => Item(i))); // 每次重建
}

// ✅ initState 中初始化
final items = List.generate(100, (i) => Item(i));

长列表优化

// ✅ ListView.builder 懒加载
ListView.builder(
  itemCount: items.length,
  itemBuilder: (context, index) => ListTile(title: Text(items[index])),
);

// ✅ cacheExtent
ListView.builder(cacheExtent: 200, itemBuilder: ...);

// ✅ RepaintBoundary 隔离重绘
RepaintBoundary(child: MyComplexWidget());

响应式布局实战

自适应 Scaffold

class AdaptiveScaffold extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    final width = MediaQuery.of(context).size.width;

    if (width < 600) {
      return Scaffold(
        body: body,
        bottomNavigationBar: NavigationBar(
          selectedIndex: currentIndex,
          onDestinationSelected: onIndexChanged,
          destinations: _destinations,
        ),
      );
    }

    return Scaffold(
      body: Row(
        children: [
          NavigationRail(
            selectedIndex: currentIndex,
            onDestinationSelected: onIndexChanged,
            labelType: width > 840
                ? NavigationRailLabelType.all
                : NavigationRailLabelType.selected,
            destinations: _destinations
                .map((d) => NavigationRailDestination(
                      icon: d.icon,
                      label: d.label,
                    ))
                .toList(),
          ),
          const VerticalDivider(thickness: 1, width: 1),
          Expanded(child: body),
        ],
      ),
    );
  }
}

响应式列数

LayoutBuilder(
  builder: (context, constraints) {
    final cols = constraints.maxWidth > 900 ? 3
               : constraints.maxWidth > 600 ? 2
               : 1;
    return GridView.count(
      crossAxisCount: cols,
      childAspectRatio: 1.5,
      children: items.map((item) => Card(child: item)).toList(),
    );
  },
);

详细参考：adaptive-responsive.md | large-screens.md

平台适配

平台检测

final idiom = MediaQuery.of(context).size.shortestSide >= 600 ? 'tablet' : 'phone';
final platform = Theme.of(context).platform;

键盘快捷键

Shortcuts(
  shortcuts: {
    LogicalKeySet(LogicalKeyboardKey.control, LogicalKeyboardKey.keyS): SaveIntent(),
  },
  child: Actions(
    actions: { SaveIntent: CallbackAction(onInvoke: (_) => _save()) },
    child: focusNode,
  ),
)

鼠标 Hover

MouseRegion(
  onEnter: (_) => setState(() => _isHovered = true),
  onExit: (_) => setState(() => _isHovered = false),
  child: MyWidget(),
)

详细参考：platform-idioms.md

避坑指南

State 管理

布局

M3 迁移

快速参考

热重载 vs 热重启

常用 EdgeInsets

EdgeInsets.all(16.0)
EdgeInsets.symmetric(v: 8)
EdgeInsets.only(left: 16)
EdgeInsets.fromLTRB(4,8,4,8)

AnimationController 生命周期

_controller = AnimationController(
  duration: Duration(milliseconds: 300),
  vsync: this,
);

@override
void dispose() {
  _controller.dispose();
  super.dispose();
}

组件速查

详细参考：buttons-input.md | navigation-components.md | display-components.md

来源

文档版本：Flutter 3.x + Material 3 URL: https://flutter.cn/docs 抓取时间：2026-04-24

参考文档

| testing.md | 参考文档：测试指南 |

单元测试（flutter_test）

详见 testing.md（flutter_test / widget / integration / Mock）

class CounterModel extends ChangeNotifier {
  int _count = 0;
  int get count => _count;
  void increment() { _count++; notifyListeners(); }
}

test('CounterModel increments correctly', () {
  final model = CounterModel();
  expect(model.count, 0);
  model.increment();
  expect(model.count, 1);
});

Widget 测试

testWidgets('CounterWidget displays count and increments', (tester) async {
  await tester.pumpWidget(MaterialApp(home: CounterWidget()));
  expect(find.text('0'), findsOneWidget);
  await tester.tap(find.byIcon(Icons.add));
  await tester.pump();
  expect(find.text('1'), findsOneWidget);
});

Riverpod Provider 测试

testProvider('counterProvider increments', (override) async {
  await runProviderScope((ref) async {
    final counter = ref.watch(counterProvider);
    expect(counter, 0);
    ref.read(counterProvider.notifier).increment();
    expect(ref.watch(counterProvider), 1);
  }, overrides: []);
});

集成测试

setUpAll(() async { await FlutterDriver.connect(); });

test('app loads and shows home', () async {
  final driver = await FlutterDriver.connect();
  await driver.waitFor(find.byType('MyHomePage'));
  expect(find.text('Home'), findsOneWidget);
});

Mock + mockito

@GenerateMocks([UserRepository])
void main() {
  late MockUserRepository mockRepo;
  setUp(() { mockRepo = MockUserRepository(); });

  test('loads user data', () async {
    when(mockRepo.getUser('123'))
        .thenAnswer((_) async => User(id: '123', name: 'Alice'));
    final user = await mockRepo.getUser('123');
    expect(user.name, 'Alice');
    verify(mockRepo.getUser('123')).called(1);
  });
}

依赖注入

详见 dependency-injection.md（get_it / injectable / DI 陷阱）

import 'package:get_it/get_it.dart';
final getIt = GetIt.instance;

void setupDependencies() {
  getIt.registerLazySingleton<Dio>(() => Dio());
  getIt.registerFactory<UserRepository>(
    () => UserRepository(dio: getIt<Dio>()),
  );
  getIt.registerSingleton<SharedPreferences>(prefs);
}

final repo = getIt<UserRepository>();

Riverpod + get_it

final dioProvider = Provider<Dio>((ref) => getIt<Dio>());
final userRepoProvider = Provider<UserRepository>(
  (ref) => UserRepository(dio: ref.watch(dioProvider)),
);

injectable

@injectable
class AuthRepository {
  final Dio dio;
  AuthRepository({required this.dio});
}
// configureDependencies(); // 自动生成

DI 陷阱

输出格式规范

回复结构

1. 直接回答 — 一段简洁的话给出核心答案
2. 代码示例 — 提供完整的 Dart/Flutter 代码
3. 实现要点 — 关键步骤和注意事项
4. 避坑提醒 — 常见错误 + 正确做法

禁用格式

• ❌ 不要显式分层（避免"第一层/第二层/框架分析"等字眼）
• ❌ 不要长篇解释概念，要直接给出实现
• ❌ 不要只给代码片段，要给完整可运行的示例
• ✅ 输出应是一段干净的话 + 完整代码