main.dart
import 'package:flutter/material.dart';
import 'package:flutter_inappwebview/flutter_inappwebview.dart';
import 'package:flutter_riverpod/flutter_riverpod.dart';
import 'package:flutter_riverpod/legacy.dart';
import 'package:flutter/services.dart'; 

final navIndexProvider = StateProvider((ref) => 0);
// ローカルサーバーのインスタンス（シングルトン推奨）
final localhostServerProvider = Provider((ref) => InAppLocalhostServer());

void main() async {
 WidgetsFlutterBinding.ensureInitialized();
  // 画面の向きを横向きに固定
SystemChrome.setPreferredOrientations([
 DeviceOrientation.landscapeLeft, // 横向き（左）
// DeviceOrientation.landscapeRight, // 横向き（右）
 ]).then((_) {
   runApp(ProviderScope(child: MaterialApp(
   debugShowCheckedModeBanner: false, 
   home: MainScreen()
    )));
  });
}

class MainScreen extends ConsumerStatefulWidget {
 @override
 _MainScreenState createState() => _MainScreenState();
}
class _MainScreenState extends ConsumerState {
 InAppWebViewController? webViewController;
 final List pages = ["index1.html", "index2.html", "index3.html"];
 @override
  void initState() {
  super.initState();
  // ローカルサーバーの起動
  ref.read(localhostServerProvider).start();
 }
@override
 Widget build(BuildContext context) {
 final selectedIndex = ref.watch(navIndexProvider);
 return Scaffold(
  body: Row(
  children: [
   NavigationRail(
   selectedIndex: selectedIndex,
   onDestinationSelected: (index) {
   ref.read(navIndexProvider.notifier).state = index;
   webViewController?.loadUrl(
   urlRequest: URLRequest(
   url: WebUri("http://localhost:8080/html/${pages[index]}"),
   ),
 );
},
 labelType: NavigationRailLabelType.all,
 backgroundColor: Colors.transparent, 
 destinations: const [
 NavigationRailDestination(icon: Icon(Icons.home), label: Text('Home')),
 NavigationRailDestination(icon: Icon(Icons.settings), label: Text('Settings')),
 NavigationRailDestination(icon: Icon(Icons.favorite), label: Text('Category C')),
 ],
),
 const VerticalDivider(thickness: 1, width: 1),
   // メインコンテンツ (WebView)
 Expanded(
  child: InAppWebView(
  initialUrlRequest: URLRequest(
// url: WebUri("http://localhost:8080/html/index1.html")
  url: WebUri("http://localhost:8080/html/${pages[selectedIndex]}"),
 ),
 onWebViewCreated: (controller) {
   webViewController = controller;
  },
  ),
  ),
  ],
 ),
 );
}
@override
 void dispose() {
  // サーバーの停止
 ref.read(localhostServerProvider).close();
 super.dispose();
 }
}

//タグの属性に
//android:usesCleartextTraffic="true"
//を設定します。こうすると、
//Androidアプリからのすべての通信でHTTPが許可されます。
 //flutter_inappwebview: ^6.1.5
 // assets:
 //   - html/index2.html
 //   - html/joy/assets/
 //   - html/joy/index.html
 //   - html/index1.html
 //   - html/css/
 //   - html/js/
//    - html/index3.html