import 'package:flutter/material.dart';
import 'package:flutter/rendering.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(),
    );
  }
}

class MyHomePage extends StatefulWidget {
  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  ScrollController _scrollController;

  @override
  void initState() {
    super.initState();
    _scrollController = ScrollController();
  }

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

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('widget.title'),
      ),
      body: Center(
        child: NotificationListener<ScrollNotification>(
          onNotification: (notification) {
            if (_scrollController.position.userScrollDirection == ScrollDirection.forward) {
              print('↑↑↑');
            } else if (_scrollController.position.userScrollDirection == ScrollDirection.reverse) {
              print('↓↓↓');
            } else if (_scrollController.position.userScrollDirection == ScrollDirection.idle) {
              print('scroll is being recognized as IDLE');
            }
          },
          child: MyListView(_scrollController),
        ),
      ), // This trailing comma makes auto-formatting nicer for build methods.
    );
  }
}

class MyListView extends StatelessWidget {
  final ScrollController scrollController;
  MyListView(this.scrollController);
  @override
  Widget build(BuildContext context) {
    return ListView.builder(
      controller: scrollController,
      itemExtent: 250.0,
      itemBuilder: (context, index) => Container(
        padding: EdgeInsets.all(10.0),
        child: Material(
          elevation: 4.0,
          borderRadius: BorderRadius.circular(5.0),
          color: index % 2 == 0 ? Colors.cyan : Colors.deepOrange,
          child: Center(
            child: Text(index.toString()),
          ),
        ),
      ),
    );
  }
}