如何在SliverAppBar上创建一个动作按钮(不是真的，它只是一个文本框)

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        body: CustomScrollView(
          slivers: <Widget>[
            SliverAppBar(
              expandedHeight: 180.0,
              floating: false,
              pinned: true,
              flexibleSpace: FlexibleSpaceBar(
                title: Text('SliverAppBar Demo'),
                background: Image.network(
                  'https://via.placeholder.com/350x150',
                  fit: BoxFit.cover,
                ),
              ),
              actions: <Widget>[
                // 这里我们使用TextButton来模拟一个动作按钮
                TextButton(
                  onPressed: () {
                    // 动作按钮的点击事件
                    print('Action button pressed!');
                  },
                  child: Text(
                    'Action',
                    style: TextStyle(
                      color: Colors.white,
                      fontSize: 16.0,
                      fontWeight: FontWeight.bold,
                    ),
                  ),
                ),
              ],
            ),
            SliverList(
              delegate: SliverChildBuilderDelegate(
                (BuildContext context, int index) {
                  return ListTile(title: Text('Item $index'));
                },
                childCount: 50,
              ),
            ),
          ],
        ),
      ),
    );
  }
}