Flutter: bottomAppBar列表视图滚动位置

import 'package:flutter/material.dart';

class MyPage extends StatefulWidget {
  @override
  _MyPageState createState() => _MyPageState();
}

class _MyPageState extends State<MyPage> {
  ScrollController _scrollController = ScrollController();
  double _scrollPosition = 0;

  @override
  void initState() {
    super.initState();
    _scrollController.addListener(_scrollListener);
  }

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

  void _scrollListener() {
    setState(() {
      _scrollPosition = _scrollController.offset;
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('My App'),
      ),
      bottomNavigationBar: BottomAppBar(
        child: Container(
          height: 50.0,
          child: Center(
            child: Text('Scroll position: $_scrollPosition'),
          ),
        ),
      ),
      body: ListView.builder(
        controller: _scrollController,
        itemBuilder: (context, index) => ListTile(
          title: Text('Item $index'),
        ),
        itemCount: 100,
      ),
    );
  }
}