在Flutter中，处理页面未找到（404）的情况通常可以通过自定义路由和错误处理来实现。虽然Flutter本身没有内置的“page_not_found”插件，但你可以通过以下步骤来实现类似的功能。

1. 自定义路由

你可以使用 MaterialApp 的 onGenerateRoute 属性来自定义路由处理逻辑。当路由未找到时，可以跳转到一个自定义的“页面未找到”页面。

import 'package:flutter/material.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  [@override](/user/override)
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      // 自定义路由处理
      onGenerateRoute: (settings) {
        // 根据路由名称处理不同的页面
        switch (settings.name) {
          case '/':
            return MaterialPageRoute(builder: (context) => HomePage());
          case '/about':
            return MaterialPageRoute(builder: (context) => AboutPage());
          default:
            // 如果路由未找到，跳转到404页面
            return MaterialPageRoute(builder: (context) => NotFoundPage());
        }
      },
      initialRoute: '/',
    );
  }
}

class HomePage extends StatelessWidget {
  [@override](/user/override)
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Home'),
      ),
      body: Center(
        child: Text('Home Page'),
      ),
    );
  }
}

class AboutPage extends StatelessWidget {
  [@override](/user/override)
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('About'),
      ),
      body: Center(
        child: Text('About Page'),
      ),
    );
  }
}

class NotFoundPage extends StatelessWidget {
  [@override](/user/override)
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('404'),
      ),
      body: Center(
        child: Text('Page Not Found'),
      ),
    );
  }
}

2. 使用 onUnknownRoute

你还可以使用 MaterialApp 的 onUnknownRoute 属性来处理未知路由。当 onGenerateRoute 没有处理某个路由时，onUnknownRoute 会被调用。

import 'package:flutter/material.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  [@override](/user/override)
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      // 自定义路由处理
      onGenerateRoute: (settings) {
        switch (settings.name) {
          case '/':
            return MaterialPageRoute(builder: (context) => HomePage());
          case '/about':
            return MaterialPageRoute(builder: (context) => AboutPage());
          default:
            // 如果路由未找到，返回null，让onUnknownRoute处理
            return null;
        }
      },
      // 处理未知路由
      onUnknownRoute: (settings) {
        return MaterialPageRoute(builder: (context) => NotFoundPage());
      },
      initialRoute: '/',
    );
  }
}

class HomePage extends StatelessWidget {
  [@override](/user/override)
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Home'),
      ),
      body: Center(
        child: Text('Home Page'),
      ),
    );
  }
}

class AboutPage extends StatelessWidget {
  [@override](/user/override)
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('About'),
      ),
      body: Center(
        child: Text('About Page'),
      ),
    );
  }
}

class NotFoundPage extends StatelessWidget {
  [@override](/user/override)
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('404'),
      ),
      body: Center(
        child: Text('Page Not Found'),
      ),
    );
  }
}

3. 使用第三方插件

虽然Flutter本身没有专门的“page_not_found”插件，但你可以使用一些第三方路由管理插件，如 auto_route 或 go_router，它们提供了更强大的路由管理功能，并且可以更容易地处理404页面。

例如，使用 go_router 处理404页面：

import 'package:flutter/material.dart';
import 'package:go_router/go_router.dart';

void main() {
  final router = GoRouter(
    routes: [
      GoRoute(
        path: '/',
        builder: (context, state) => HomePage(),
      ),
      GoRoute(
        path: '/about',
        builder: (context, state) => AboutPage(),
      ),
    ],
    errorBuilder: (context, state) => NotFoundPage(),
  );

  runApp(MyApp(router: router));
}

class MyApp extends StatelessWidget {
  final GoRouter router;

  MyApp({required this.router});

  [@override](/user/override)
  Widget build(BuildContext context) {
    return MaterialApp.router(
      routerConfig: router,
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
    );
  }
}

class HomePage extends StatelessWidget {
  [@override](/user/override)
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Home'),
      ),
      body: Center(
        child: Text('Home Page'),
      ),
    );
  }
}

class AboutPage extends StatelessWidget {
  [@override](/user/override)
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('About'),
      ),
      body: Center(
        child: Text('About Page'),
      ),
    );
  }
}

class NotFoundPage extends StatelessWidget {
  [@override](/user/override)
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('404'),
      ),
      body: Center(
        child: Text('Page Not Found'),
      ),
    );
  }
}