import 'package:flutter/material.dart';

final GlobalKey<NavigatorState> key = GlobalKey<NavigatorState>();
void main() => runApp(MaterialApp(
  home: Row(
    children: [
      Container(width: 100, color: Colors.red,),
      Container(width: 100 ,child: Navigator(
        key: key,
        onGenerateRoute: (RouteSettings settings) {
          return MaterialPageRoute<void>(builder: (_) {
            return Scaffold(
              appBar: AppBar(title: Text(settings.name?? '')),
              body: ElevatedButton(
                child: Text(settings.name ?? ''),
                onPressed: () {
                  key.currentState!.pushNamed('/a');
                },
              ),
            );
          });
        },
      ))
    ]
  ),
));