Get scroll distance each time user scroll a ListView - flutter

Question

Using the scrollListener and ScrollController, how can I get the scroll distance from start to the end of the scrolling each time the user scroll?

Answer 1

ScrollController has a property called offset which will give you the current offset.
A working example follows
import 'package:flutter/material.dart';
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
// This widget is the root of your application.
#override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Flutter Demo',
theme: ThemeData(
primarySwatch: Colors.blue,
),
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> {
ScrollController controller = ScrollController();
double initialPosition = 0.0;
double endPosition = 0.0;
double distance = 0.0;
#override
void initState() {
super.initState();
controller = ScrollController();
}
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text(widget.title),
),
body: NotificationListener(
onNotification: (notif) {
if(notif is ScrollStartNotification) {
initialPosition = controller.offset;
} else if(notif is ScrollEndNotification) {
endPosition = controller.offset;
distance = endPosition - initialPosition;
print(distance);
}
return true;
},
child: ListView(
controller: controller,
children: <Widget>[
Container(
height: 100.0,
color: Colors.red,
),
Container(
height: 100.0,
color: Colors.red,
),
Container(
height: 100.0,
color: Colors.red,
),
Container(
height: 100.0,
color: Colors.red,
),
Container(
height: 100.0,
color: Colors.red,
),
Container(
height: 100.0,
color: Colors.red,
),
Container(
height: 100.0,
color: Colors.red,
),
Container(
height: 100.0,
color: Colors.red,
),
Container(
height: 100.0,
color: Colors.red,
),
],
),),
);
}
}
UPDATE: Added code which helps in detecting start and end scroll.