Flutter跨平台工程实践与原理透视：从渲染引擎到高质产物

// pubspec.yaml: go_router: ^14.x
import 'package:flutter/material.dart';
import 'package:go_router/go_router.dart';

final router = GoRouter(
  routes: [
    GoRoute(path: '/', builder: (_, __) => const HomePage()),
    GoRoute(
      path: '/detail/:id',
      builder: (ctx, state) => DetailPage(id: state.params['id']!),
      redirect: (ctx, state) {
        // 关键守卫：未登录跳转登录
        final loggedIn = false; // TODO: 从Auth状态获取
        if (!loggedIn) return '/login?from=${state.uri}';
        return null;
      },
    ),
    GoRoute(path: '/login', builder: (_, s) => const LoginPage()),
  ],
);

void main() {
  runApp(MaterialApp.router(routerConfig: router));
}

// pubspec.yaml: flutter_riverpod: ^2.x
import 'package:flutter/material.dart';
import 'package:flutter_riverpod/flutter_riverpod.dart';

final counterProvider = StateProvider<int>((_) => 0);

void main() => runApp(const ProviderScope(child: App()));

class App extends StatelessWidget {
  const App({super.key});
  @override
  Widget build(BuildContext context) {
    return MaterialApp(home: Scaffold(
      appBar: AppBar(title: const Text('Riverpod Counter')),
      body: Center(child: Consumer(
        builder: (_, ref, __) {
          final count = ref.watch(counterProvider);
          return Text('Count: $count');
        },
      )),
      floatingActionButton: Consumer(
        builder: (_, ref, __) => FloatingActionButton(
          onPressed: () => ref.read(counterProvider.notifier).state++,
          child: const Icon(Icons.add),
        ),
      ),
    ));
  }
}

import 'package:flutter/material.dart';

class PhotoList extends StatelessWidget {
  final List<String> urls;
  const PhotoList({super.key, required this.urls});

  @override
  Widget build(BuildContext context) {
    return ListView.builder(
      itemCount: urls.length,
      itemBuilder: (_, i) => RepaintBoundary(
        child: ListTile(
          leading: Image.network(
            urls[i],
            cacheWidth: 200, // 降采样
            fit: BoxFit.cover,
          ),
          title: Text('Item $i'),
        ),
      ),
    );
  }
}

import 'package:flutter/services.dart';

const _ch = MethodChannel('app/native');

Future<String?> getDeviceModel() async {
  return await _ch.invokeMethod<String>('deviceModel');
}

// Android 侧（Kotlin）
class MainActivity: FlutterActivity() {
  private val channel = "app/native"
  override fun configureFlutterEngine(flutterEngine: FlutterEngine) {
    super.configureFlutterEngine(flutterEngine)
    MethodChannel(flutterEngine.dartExecutor.binaryMessenger, channel)
      .setMethodCallHandler { call, result ->
        when (call.method) {
          "deviceModel" -> result.success(Build.MODEL)
          else -> result.notImplemented()
        }
      }
  }
}

# 体积与崩溃定位
flutter build apk --split-per-abi --split-debug-info=build/symbols

// pubspec.yaml: flutter_localizations: sdk: flutter, intl: ^0.19
import 'package:flutter/material.dart';
import 'package:flutter_localizations/flutter_localizations.dart';

void main() => runApp(const MyApp());

class MyApp extends StatelessWidget {
  const MyApp({super.key});
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      localizationsDelegates: const [
        GlobalMaterialLocalizations.delegate,
        GlobalWidgetsLocalizations.delegate,
        GlobalCupertinoLocalizations.delegate,
      ],
      supportedLocales: const [Locale('en'), Locale('zh')],
      home: const Scaffold(body: Center(child: Text('Hello/你好'))),
    );
  }
}

// widget_test.dart
import 'package:flutter_test/flutter_test.dart';
import 'package:flutter/material.dart';

void main() {
  testWidgets('Counter increments smoke', (tester) async {
    int count = 0;
    await tester.pumpWidget(MaterialApp(
      home: StatefulBuilder(
        builder: (_, set) => Scaffold(
          body: Text('Count: $count', key: const Key('t')),
          floatingActionButton: FloatingActionButton(
            onPressed: () => set(() => count++),
          ),
        ),
      ),
    ));
    await tester.tap(find.byType(FloatingActionButton));
    await tester.pump();
    expect(find.text('Count: 1'), findsOneWidget);
  });
}

// 伪代码示例：网络优先，失败回落本地
Future<List<Item>> fetchItems(Api api, LocalStore store) async {
  try {
    final remote = await api.list();
    await store.save(remote);
    return remote;
  } catch (_) {
    return store.read();
  }
}