问Flutter Web首先加载初始页面，即使使用#/page加载URL时也是如此

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import 'package:flutter/material.dart';

void main() {
  runApp(MaterialApp(
    title: 'Named Routes Demo',
    routes: {
      '/': (context) => FirstScreen(),
      '/second': (context) => SecondScreen(),
    },
  ));
}

class FirstScreen extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    print ("Screen 1 building");
    return Scaffold(
      appBar: AppBar(
        title: Text('First Screen'),
      ),
      body: Center(
        child: RaisedButton(
          child: Text('Launch second screen'),
          onPressed: () {
            // Navigate to the second screen using a named route.
            Navigator.pushNamed(context, '/second');
          },
        ),
      ),
    );
  }
}

class SecondScreen extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    print ("Screen 2 building");
    return Scaffold(
      appBar: AppBar(
        title: Text("Second Screen"),
      ),
      body: Center(
        child: RaisedButton(
          onPressed: () {
            Navigator.pop(context);
          },
          child: Text('This is screen 2, go to 1!'),
        ),
      ),
    );
  }
}