如何阻止来自Navigator.pushNamed的导航...并显示底部模式？

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: HomeScreen(),
      routes: {
        '/screen1': (context) => Screen1(),
        '/screen2': (context) => Screen2(),
        '/screen3': (context) => Screen3(),
      },
    );
  }
}

class HomeScreen extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Home'),
      ),
      body: Center(
        child: Text('Home Screen'),
      ),
      bottomNavigationBar: BottomNavigationBar(
        items: [
          BottomNavigationBarItem(
            icon: Icon(Icons.home),
            label: 'Screen 1',
          ),
          BottomNavigationBarItem(
            icon: Icon(Icons.business),
            label: 'Screen 2',
          ),
          BottomNavigationBarItem(
            icon: Icon(Icons.school),
            label: 'Screen 3',
          ),
        ],
        onTap: (index) {
          if (index == 0) {
            Navigator.pushReplacementNamed(context, '/screen1');
          } else if (index == 1) {
            Navigator.pushReplacementNamed(context, '/screen2');
          } else if (index == 2) {
            Navigator.pushReplacementNamed(context, '/screen3');
          }
        },
      ),
    );
  }
}

class Screen1 extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Screen 1'),
      ),
      body: Center(
        child: Text('Screen 1'),
      ),
    );
  }
}

class Screen2 extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Screen 2'),
      ),
      body: Center(
        child: Text('Screen 2'),
      ),
    );
  }
}

class Screen3 extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Screen 3'),
      ),
      body: Center(
        child: Text('Screen 3'),
      ),
    );
  }
}