إخفاء شريط التنقل السفلي في Flutter عند التمرير

import 'package:flutter/material.dart';
import 'package:flutter/rendering.dart';

class FullPage extends StatefulWidget {
  const FullPage({Key? key}) : super(key: key);

  @override
  State<FullPage> createState() => _FullPageState();
}

class _FullPageState extends State<FullPage> {
  double bottomBarHeight = 75;
  bool isShowButton = true;
  bool isShowAppbar = true;
  bool storyCondition = false;
  bool isScrollDown = false;
  final ScrollController _scrollController = ScrollController();

  @override
  void initState() {
    super.initState();
    scroll();
  }

  @override
  void dispose() {
    super.dispose();
    _scrollController.removeListener(() { });
  }

  void showBottom(){
    setState(() {
      isShowButton = true;
    });
  }

  void hideBottom() {
    setState(() {
      isShowButton = false;
    });
  }

  void scroll() {
    _scrollController.addListener(() {
      if (_scrollController.position.userScrollDirection == ScrollDirection.reverse) {
        if (!isScrollDown) {
          isScrollDown = true;
          isShowAppbar = false;
          hideBottom();
        }
      }
      if (_scrollController.position.userScrollDirection == ScrollDirection.forward) {
        if (isScrollDown) {
          isScrollDown = false;
          isShowAppbar = true;
          showBottom();
        }

      }
    });
  }


  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: isShowAppbar
          ? AppBar(
        title: const Text('My Tasks'),
      )
          : PreferredSize(
        preferredSize: const Size(0.0, 0.0),
        child: Container(),
      ),
      bottomNavigationBar: SizedBox(
        height: isShowButton ? bottomBarHeight : 0,
        width: MediaQuery.of(context).size.width,
        child: isShowButton ?
        BottomNavigationBar(
          currentIndex: 0, // this will be set when a new tab is tapped
          items: const [
            BottomNavigationBarItem(
              icon:  Icon(Icons.home),
              label:  'Home',
            ),
            BottomNavigationBarItem(
              icon:  Icon(Icons.mail),
              label:  'Message',
            ),
            BottomNavigationBarItem(
              icon: Icon(Icons.person),
              label:  'Person',)
          ],
        )
            : Container(
          color: Colors.white,
          width: MediaQuery.of(context).size.width,
        ),
      ),
      body: listView(),
    );
  }

  Widget containterContent(int index){
    return Container(
      height: 50.0,
      color: Colors.cyanAccent,
      margin: const EdgeInsets.all(8.0),
      width: MediaQuery.of(context).size.width - 100,
      child: Center(child: Text('Item $index',
        style: const TextStyle(
          fontSize: 14.0,
        ),)),
    );
  }

  ListView listView() {
    return ListView(
      controller: _scrollController,
      children: [
        for (int i = 0 ; i<30 ; i++)
        containterContent(i),

      ],
    );
  }

}