You can copy paste run full code below 
You can use bottomSheet and wrap AppBar with Container set kToolbarHeight 
bottomSheet: Container(
        height: kToolbarHeight,
        child: AppBar(
          title: Text("bottom sheet"),
        ),
      ),
working demo

full code
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,
        visualDensity: VisualDensity.adaptivePlatformDensity,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}
class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);
  final String title;
  @override
  _MyHomePageState createState() => _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
  int _counter = 0;
  void _incrementCounter() {
    setState(() {
      _counter++;
    });
  }
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Expanded(
              child: ListView(
                  children:
                      List.generate(100, (i) => Text("line" + i.toString()))),
            ),
          ],
        ),
      ),
      bottomSheet: Container(
        height: kToolbarHeight,
        child: AppBar(
          title: Text("bottom sheet"),
        ),
      ),
    );
  }
}