Flutter懒加载插件flutter_lazy_loading的使用
Flutter懒加载插件flutter_lazy_loading的使用
flutter_lazy_loading 是一个用于实现懒加载（Lazy Loading）功能的小型Flutter插件。它提供了流畅的滚动和加载项体验，适用于需要分页、无限滚动等场景的应用。
Features 特性
- 以
ListView或GridView的形式加载项目 - 当用户滚动时加载更多项目
- 使用构建器函数高效地创建可滚动的列表或网格
- 实现非常简单
Getting Started 开始使用
安装依赖
- 在
pubspec.yaml文件中添加flutter_lazy_loading包到依赖部分：dependencies: flutter_lazy_loading: ^latest_version - 或者在项目根目录下运行以下命令来添加该包：
flutter pub add flutter_lazy_loading - 然后添加
provider包：flutter pub add provider
Usage 使用方法
创建 LazyLoadingProvider
首先，在你想要添加懒加载组件的地方，创建一个 LazyLoadingProvider 实例。例如，假设我们要展示书籍数据：
ChangeNotifierProvider<LazyLoadingProvider<Books>>(
create: (context) => LazyLoadingProvider<Books>(
fetchItems: ItemsController().fetchItems,
firstPageNumber: 1,
offset: 9,
),
child: Consumer<LazyLoadingProvider<Books>>(
builder: (context, provider, _) {
return LazyLoadingWidget(
provider: provider,
gridView: true,
gridViewCrossAxisCount: 3,
itemWidget: (book) {
// 返回每个项目的UI布局
return Container(
decoration: BoxDecoration(
borderRadius: BorderRadius.circular(24),
color: Colors.purple.shade200,
),
margin: const EdgeInsets.all(8),
padding: const EdgeInsets.all(8),
child: Column(
children: [
Row(
crossAxisAlignment: CrossAxisAlignment.center,
children: [
Text("Price: "),
SizedBox(height: 20),
Row(
mainAxisSize: MainAxisSize.min,
children: [
Text(book.mrp.toString(),
style: TextStyle(
color: Colors.black,
fontSize: 16,
fontWeight: FontWeight.bold,
)),
SizedBox(width: 10),
Text(book.mrp.toString(),
style: TextStyle(
color: Colors.black26,
fontSize: 16,
decoration: TextDecoration.lineThrough)),
],
)
],
),
SizedBox(height: 20),
Text(
book.title,
style: TextStyle(fontSize: 14, fontWeight: FontWeight.bold),
textAlign: TextAlign.center,
),
SizedBox(height: 5),
Text(
book.description,
style: TextStyle(fontSize: 12, color: Colors.black54),
maxLines: 2,
overflow: TextOverflow.ellipsis,
textAlign: TextAlign.center,
),
],
),
);
},
);
},
),
)
定义 Fetch 方法
定义一个异步方法 fetchItems，该方法根据页码和偏移量获取数据，并将结果转换为 ItemsResponse 对象：
Future<ItemsResponse<Books>?> fetchItems(int page, int offset) async {
List<Books> books = <Books>[];
num end = page * offset;
num start = end - offset;
for (var i = start; i < (end.toInt() <= booksDataBase.length ? end.toInt() : booksDataBase.length); i++) {
final bookData = booksDataBase[i.toInt()];
final book = Books.fromJson(bookData);
if (book != null) {
books.add(book);
}
}
await Future.delayed(Duration(seconds: 2));
print(books);
return books.isNotEmpty
? ItemsResponse<Books>(items: books, totalPages: booksDataBase.length ~/ offset)
: null;
}
完整示例 Demo
以下是一个完整的示例，展示了如何使用 flutter_lazy_loading 插件来展示书籍列表：
import 'package:flutter/material.dart';
import 'package:flutter_lazy_loading/flutter_lazy_loading.dart';
import 'package:provider/provider.dart';
void main() {
runApp(const MyApp());
}
class MyApp extends StatelessWidget {
const MyApp({Key? key}) : super(key: key);
[@override](/user/override)
Widget build(BuildContext context) {
return MaterialApp(
debugShowCheckedModeBanner: false,
home: HomePage(),
);
}
}
class HomePage extends StatelessWidget {
const HomePage({Key? key}) : super(key: key);
[@override](/user/override)
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(title: Text("Book Shop")),
body: Column(
children: [
Padding(
padding: const EdgeInsets.symmetric(horizontal: 8.0, vertical: 10.0),
child: Row(
children: [
Expanded(
child: Text(
"Top Selling Books",
style: TextStyle(fontSize: 24, color: Theme.of(context).colorScheme.primary),
),
),
],
),
),
Expanded(
child: ChangeNotifierProvider<LazyLoadingProvider<Books>>(
create: (context) => LazyLoadingProvider<Books>(
fetchItems: ItemsController().fetchItems,
firstPageNumber: 1,
offset: 9,
),
child: Consumer<LazyLoadingProvider<Books>>(
builder: (context, provider, _) {
return LazyLoadingWidget(
provider: provider,
gridView: true,
gridViewCrossAxisCount: 3,
itemWidget: (book) {
return Container(
decoration: BoxDecoration(
borderRadius: BorderRadius.circular(24),
color: Colors.purple.shade200,
),
margin: const EdgeInsets.all(8),
padding: const EdgeInsets.all(8),
child: Column(
children: [
Row(
crossAxisAlignment: CrossAxisAlignment.center,
children: [
Text("Price: "),
SizedBox(height: 20),
Row(
mainAxisSize: MainAxisSize.min,
children: [
Text(book.mrp.toString(),
style: TextStyle(
color: Colors.black,
fontSize: 16,
fontWeight: FontWeight.bold,
)),
SizedBox(width: 10),
Text(book.mrp.toString(),
style: TextStyle(
color: Colors.black26,
fontSize: 16,
decoration: TextDecoration.lineThrough)),
],
),
],
),
SizedBox(height: 20),
Text(
book.title,
style: TextStyle(fontSize: 14, fontWeight: FontWeight.bold),
textAlign: TextAlign.center,
),
SizedBox(height: 5),
Text(
book.description,
style: TextStyle(fontSize: 12, color: Colors.black54),
maxLines: 2,
overflow: TextOverflow.ellipsis,
textAlign: TextAlign.center,
),
],
),
);
},
);
},
),
),
),
],
),
);
}
}
// 其他类定义...
更多关于Flutter懒加载插件flutter_lazy_loading的使用的实战系列教程也可以访问 https://www.itying.com/category-92-b0.html
