将布局放置在AppBar下(类似于Messenger)

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(),
    );
  }
}

class MyHomePage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('My App'),
      ),
      body: Column(
        children: [
          Expanded(
            child: ListView(
              children: [
                ListTile(
                  title: Text('Message 1'),
                ),
                ListTile(
                  title: Text('Message 2'),
                ),
                ListTile(
                  title: Text('Message 3'),
                ),
                // 添加更多的消息列表项
              ],
            ),
          ),
          Container(
            padding: EdgeInsets.all(16.0),
            child: TextField(
              decoration: InputDecoration(
                hintText: 'Type a message...',
              ),
            ),
          ),
        ],
      ),
    );
  }
}