将列添加到底部appbar使其全屏显示

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          title: Text('My App'),
        ),
        body: Container(
          child: Center(
            child: Text('Hello World'),
          ),
        ),
        extendBody: true,
        bottomNavigationBar: BottomAppBar(
          shape: CircularNotchedRectangle(),
          child: Container(
            height: kToolbarHeight,
            child: Column(
              children: [
                Text('This is the bottom app bar'),
                Text('Here you can add more content'),
              ],
            ),
          ),
        ),
        floatingActionButton: FloatingActionButton(
          child: Icon(Icons.add),
          onPressed: () {},
        ),
        floatingActionButtonLocation: FloatingActionButtonLocation.centerDocked,
      ),
    );
  }
}