Flutter Lazy Loader with Example

In Flutter, a lazy loader allows you to load data on demand or as it is needed, instead of loading all data at once. This can help to improve the performance of your app and reduce the amount of memory used by your app.

In this blog, we will discuss how to implement a lazy loader in Flutter with an example.

Step 1: Importing the Required Packages

The first step is to import the required packages for the lazy loader. In this example, we will be using the ListView.builder widget from the Flutter framework and the faker package to generate random data. Add the following lines to your pubspec.yaml file to install the faker package:

dependencies:
  faker: ^3.0.1​

After that, run flutter pub get to install the package.

Next, import the required packages in your main.dart file:

import 'package:flutter/material.dart';
import 'package:faker/faker.dart';​

Step 2: Creating a Lazy Loader Widget

To create a lazy loader widget, we will use the ListView.builder widget from the Flutter framework. This widget creates a scrollable list that lazily loads data as the user scrolls.

Here is an example of how to use the ListView.builder widget to create a lazy loader:

class LazyLoader extends StatefulWidget {
  @override
  _LazyLoaderState createState() => _LazyLoaderState();
}
class _LazyLoaderState extends State<LazyLoader> {
  final faker = Faker();
  final _itemsPerPage = 10;
  var _isLoading = false;
  var _items = <String>[];
  @override
  void initState() {
    super.initState();
    _loadMoreItems();
  }
  Future<void> _loadMoreItems() async {
    setState(() {
      _isLoading = true;
    });
    // Simulate a delay to fetch data
    await Future.delayed(Duration(seconds: 2));
    setState(() {
      _items.addAll(List.generate(_itemsPerPage, (index) => faker.lorem.sentence()));
      _isLoading = false;
    });
  }
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Lazy Loader'),
      ),
      body: ListView.builder(
        itemCount: _items.length + (_isLoading ? 1 : 0),
        itemBuilder: (context, index) {
          if (index == _items.length) {
            return Center(
              child: CircularProgressIndicator(),
            );
          } else {
            return ListTile(
              title: Text(_items[index]),
            );
          }
        },
        onScrollEndDrag: (_) {
          if (!_isLoading && _items.length < 100) {
            _loadMoreItems();
          }
        },
      ),
    );
  }
}​

In this example, we have created a stateful widget called LazyLoader that contains a ListView.builder widget. We have also defined some properties for the lazy loader, such as the number of items to load per page, whether or not the loader is currently loading more data, and an array to store the loaded data.

In the initState method, we load the initial set of data by calling the _loadMoreItems method. This method sets the _isLoading property to true, simulates a delay to fetch data, adds the loaded data to the _items array, and sets the _isLoading property to false.

In the build method, we render the ListView.builder widget with the loaded data. If the loader is currently loading more data, we display a CircularProgressIndicator widget at the bottom of the list.