scrollController get offset (slow!!!! _scrollController.addListener)

 _scrollController.addListener is too slow!!!! use timer.periodic to do parallax scrolling

 import 'package:flutter/material.dart';

void main() {

runApp(const MyApp());

}

class MyApp extends StatelessWidget {

const MyApp({Key? key}) : super(key: key);

// This widget is the root of your application.

@override

Widget build(BuildContext context) {

return MaterialApp(

title: 'Flutter Demo',

theme: ThemeData(

primarySwatch: Colors.blue,

),

home: const MyHomePage(title: 'Flutter Demo Home Page'),

);

}

}

class MyHomePage extends StatefulWidget {

const MyHomePage({Key? key, required this.title}) : super(key: key);

final String title;

@override

State<MyHomePage> createState() => _MyHomePageState();

}

class _MyHomePageState extends State<MyHomePage> {

final ScrollController _scrollController = ScrollController(

initialScrollOffset: 0.0,

keepScrollOffset: true,

);

@override

void initState() {

super.initState();

print('init');

_scrollController.addListener(() { //very slow

print('_scrollController.offset: '+_scrollController.offset.toString());

});

}

@override

Widget build(BuildContext context) {

return Scaffold(

appBar: AppBar(

title: Text(widget.title),

),

body: Container(

width: double.infinity,

height: double.infinity,

child: SingleChildScrollView(

controller: _scrollController,

child: Column(children: [

Text('start', style: TextStyle(height: 2, fontSize: 30)),

Text('1234', style: TextStyle(height: 2, fontSize: 30)),

Text('1234', style: TextStyle(height: 2, fontSize: 30)),

Text('1234', style: TextStyle(height: 2, fontSize: 30)),

Text('1234', style: TextStyle(height: 2, fontSize: 30)),

Text('1234', style: TextStyle(height: 2, fontSize: 30)),

Text('1234', style: TextStyle(height: 2, fontSize: 30)),

Text('1234', style: TextStyle(height: 2, fontSize: 30)),

Text('1234', style: TextStyle(height: 2, fontSize: 30)),

Text('1234', style: TextStyle(height: 2, fontSize: 30)),

Text('1234', style: TextStyle(height: 2, fontSize: 30)),

Text('1234', style: TextStyle(height: 2, fontSize: 30)),

Text('1234', style: TextStyle(height: 2, fontSize: 30)),

Text('1234', style: TextStyle(height: 2, fontSize: 30)),

Text('1234', style: TextStyle(height: 2, fontSize: 30)),

Text('1234', style: TextStyle(height: 2, fontSize: 30)),

Text('1234', style: TextStyle(height: 2, fontSize: 30)),

Text('1234', style: TextStyle(height: 2, fontSize: 30)),

Text('1234', style: TextStyle(height: 2, fontSize: 30)),

Text('1234', style: TextStyle(height: 2, fontSize: 30)),

Text('end', style: TextStyle(height: 2, fontSize: 30)),

]))),

);

}

}