bottomnavbar.dart

import 'package:flutter/material.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Material App',
      home: Scaffold(
        bottomNavigationBar: BottomNavigationBar(
          items: [
            BottomNavigationBarItem(icon: Icon(Icons.ac_unit), label: 'Hello'),
            BottomNavigationBarItem(icon: Icon(Icons.ac_unit), label: 'Hello'),
          ],
        ),
        appBar: AppBar(
          title: Text('Material App Bar'),
        ),
        body: Navigator(
          onGenerateRoute: (_) => MaterialPageRoute(
            builder: (ctx) => Center(
              child: Container(
                child: ElevatedButton(
                  onPressed: () {
                    showModalBottomSheet(
                      context: ctx,
                      builder: (context) => Container(
                        color: Colors.blue,
                        height: 50,
                        width: MediaQuery.of(context).size.width,
                      ),
                    );
                  },
                  child: Text('Hello World'),
                ),
              ),
            ),
          ),
        ),
      ),
    );
  }
}