The Lazy loader is a wrapper to the ScrollView that enables lazy loading. It is very useful in situations where the application's intent is to show endless content in a ListView. For instance, Instagram, Facebook, Youtube and most social networking platforms use them to deliver an endless stream of content.
In this article, we will look into the process of implementing Lazy loader to an application by building a simple app with endless content. For the sake of simplicity, we will use a single content and make a copy of it for the rest of the content in the app. To do so follow the below steps:
Steps to implement Lazy Loader in Flutter
Step 1 : Adding the dependency
The Lazy loader can be added to the dependencies of the pubspec.yaml file as shown below:
dependencies:
lazy_load_scrollview: ^1.3.0Now run the below command in terminal
flutter pub get
Step 2 : Importing the dependency
The following line of code can be added to the main.dart file to import the lazy_load_scrollview dependency:
import 'package:lazy_load_scrollview/lazy_load_scrollview.dart';
Step 3 : Creating the Homepage
A StatefulWidget can be extended to form a simple Homepage for the application as shown below:
Dart
class MyApp extends StatelessWidget {
//root of the application
@override
Widget build(BuildContext context) {
return new MaterialApp(
title: 'Example',
home: new MyHomePage(title: 'GeeksForGeeks'),
);
}
}
class MyHomePage extends StatefulWidget {
MyHomePage({Key key, this.title}) : super(key: key);
final String title;
@override
_MyHomePageState createState() => new _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
List<int> data = [];
int currentLength = 0;
final int increment = 10;
bool isLoading = false;
@override
void initState() {
_loadMore();
super.initState();
}
Future _loadMore() async {
setState(() {
isLoading = true;
});
// dummy delay
await new Future.delayed(const Duration(seconds: 2));
for (var i = currentLength; i <= currentLength + increment; i++) {
data.add(i);
}
setState(() {
isLoading = false;
currentLength = data.length;
});
}
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text(widget.title),
backgroundColor: Colors.green,
foregroundColor: Colors.white,
),
// contents of the app goes here
body:
),
);
}
}
Step 4 : Calling the LazyLoaderScrollView
The LazyLoaderScrollView is a method provided by the lazy_load_scrollview package that is used to implement lazy loading to the app and can be implemented as shown below:
Dart
LazyLoadScrollView(
isLoading: isLoading,
onEndOfPage: () => _loadMore(),
child: ListView.builder(
itemCount: data.length,
itemBuilder: (context, position) {
return DemoItem(position);
To know more about ListView refer this article: ListView Class in Flutter
Step 5 : Designing the Content
Here again, a StatelessWidget can be extended to a body of text content that gets loaded infinitely by the app as shown below:
Dart
class DemoItem extends StatelessWidget {
final int position;
const DemoItem(
this.position, {
Key key,
}) : super(key: key);
@override
Widget build(BuildContext context) {
return Card(
child: Padding(
padding: const EdgeInsets.all(8.0),
child: Column(
crossAxisAlignment: CrossAxisAlignment.start,
children: <Widget>[
Row(
crossAxisAlignment: CrossAxisAlignment.center,
children: <Widget>[
Container(
color: Colors.deepOrange,
height: 40.0,
width: 40.0,
),
SizedBox(width: 8.0),
Text("Item $position"),
],
),
Text(
"GeeksforGeeks.org was created with a goal "
"in mind to provide well written, well "
"thought and well explained solutions for selected"
" questions. The core team of five super geeks"
" constituting of technology lovers and computer"
" science enthusiasts have been constantly working"
" in this direction ."),
],
),
),
);
}
}
Complete Source Code (main.dart):
main.dart
import 'package:flutter/material.dart';
import 'package:lazy_load_scrollview/lazy_load_scrollview.dart';
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
@override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Example',
home: MyHomePage(title: 'GeeksForGeeks'),
debugShowCheckedModeBanner: false,
);
}
}
class MyHomePage extends StatefulWidget {
MyHomePage({super.key, required this.title});
final String title;
@override
_MyHomePageState createState() => _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
List<int> data = [];
int currentLength = 0;
final int increment = 10;
bool isLoading = false;
@override
void initState() {
_loadMore();
super.initState();
}
Future _loadMore() async {
setState(() {
isLoading = true;
});
// Add a delay
await Future.delayed(const Duration(seconds: 2));
for (var i = currentLength; i <= currentLength + increment; i++) {
data.add(i);
}
setState(() {
isLoading = false;
currentLength = data.length;
});
}
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text(widget.title),
backgroundColor: Colors.green,
foregroundColor: Colors.white,
),
body: Column(
children: [
Expanded(
child: LazyLoadScrollView(
isLoading: isLoading,
onEndOfPage: () => _loadMore(),
child: ListView.builder(
itemCount: data.length,
itemBuilder: (context, position) {
return DemoItem(position);
},
),
),
),
if (isLoading)
Center(
child: Padding(
padding: const EdgeInsets.symmetric(vertical: 8),
child: CircularProgressIndicator(
color: Colors.green.shade900,
),
),
),
],
),
);
}
}
class DemoItem extends StatelessWidget {
final int position;
const DemoItem(
this.position, {
super.key,
});
@override
Widget build(BuildContext context) {
return Card(
child: Padding(
padding: const EdgeInsets.all(8.0),
child: Column(
crossAxisAlignment: CrossAxisAlignment.start,
children: <Widget>[
Row(
crossAxisAlignment: CrossAxisAlignment.center,
children: <Widget>[
Container(
color: Colors.deepOrange,
height: 40.0,
width: 40.0,
),
SizedBox(width: 8.0),
Text("Item $position"),
],
),
Text(
"GeeksforGeeks.org was created with a goal "
"in mind to provide well written, well "
"thought and well explained solutions for selected"
" questions. The core team of five super geeks"
" constituting of technology lovers and computer"
" science enthusiasts have been constantly working"
" in this direction."
),
],
),
),
);
}
}
Output:
Explore
Basics
Key Widgets
UI Components
Design & Animations
Forms & Gestures
Navigation & Routing
Hardware Interaction
Sample Flutter Apps
Advance Concepts