Flutter -如何在ListView.separated顶部插入有状态窗口小部件？

import 'package:flutter/material.dart';

class TopWidget extends StatefulWidget {
  @override
  _TopWidgetState createState() => _TopWidgetState();
}

class _TopWidgetState extends State<TopWidget> {
  @override
  Widget build(BuildContext context) {
    return Container(
      height: 100,
      color: Colors.blue,
      child: Center(
        child: Text(
          'Top Widget',
          style: TextStyle(
            color: Colors.white,
            fontSize: 20,
          ),
        ),
      ),
    );
  }
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          title: Text('ListView with Top Widget'),
        ),
        body: ListView.builder(
          itemCount: 10,
          itemBuilder: (BuildContext context, int index) {
            if (index == 0) {
              return TopWidget();
            }
            return ListTile(
              title: Text('Item $index'),
            );
          },
          separatorBuilder: (BuildContext context, int index) {
            return Divider();
          },
        ),
      ),
    );
  }
}

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