Infinite Scroll Pagination for Flutter Applications

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Infinite Scroll Pagination for Flutter Applications

Infinite scroll pagination, also known as endless scrolling, lazy loading, or progressive loading, is a technique used to load data incrementally as the user scrolls down a list. This approach enhances the user experience by eliminating the need for manual pagination or loading indicators.

The 'infinite_scroll_pagination' package provides a comprehensive solution for implementing infinite scrolling in Flutter applications. It offers an unopinionated, extensible, and highly customizable API that seamlessly integrates with various state management approaches and layout widgets.

Getting Started

To start using the 'infinite_scroll_pagination' package, add it as a dependency to your Flutter project's 'pubspec.yaml' file:

dependencies:
  infinite_scroll_pagination: ^X.Y.Z

Next, import the package into your Dart code:

import 'package:infinite_scroll_pagination/infinite_scroll_pagination.dart';

Core Concepts

The package includes two key components:

  • PagingController: Manages the pagination logic, including fetching data from your API, managing the page state, and triggering page requests.
  • PagedChildBuilderDelegate: Defines how to build and display the paginated items.

Basic Usage

The following code snippet demonstrates a basic implementation of infinite scrolling pagination in a Flutter application:

class BeerListView extends StatefulWidget {
  // Define the page size for each request
  static const _pageSize = 20;

  @override
  _BeerListViewState createState() => _BeerListViewState();
}

class _BeerListViewState extends State {
  // Create the PagingController
  final PagingController _pagingController = PagingController(firstPageKey: 0);

  @override
  void initState() {
    // Add a listener to the PagingController to fetch new data as the user scrolls
    _pagingController.addPageRequestListener((pageKey) {
      _fetchPage(pageKey);
    });

    super.initState();
  }

  // Fetch a page of data from the API
  Future _fetchPage(int pageKey) async {
    try {
      // Simulate API call by fetching a list of items
      final newItems = await RemoteApi.getBeerList(pageKey, BeerListView._pageSize);

      // Check if it's the last page
      final isLastPage = newItems.length < BeerListView._pageSize;

      // Append the new items to the PagingController
      if (isLastPage) {
        _pagingController.appendLastPage(newItems);
      } else {
        final nextPageKey = pageKey + newItems.length;
        _pagingController.appendPage(newItems, nextPageKey);
      }
    } catch (error) {
      // Handle error by setting it on the PagingController
      _pagingController.error = error;
    }
  }

  // Build the PagedListView widget
  @override
  Widget build(BuildContext context) => PagedListView(
    pagingController: _pagingController,
    builderDelegate: PagedChildBuilderDelegate(
      itemBuilder: (context, item, index) => BeerListItem(beer: item),
    ),
  );

  @override
  void dispose() {
    // Dispose the PagingController when the widget is disposed
    _pagingController.dispose();
    super.dispose();
  }
}

Key Features

  • State Management Agnostic: Works seamlessly with any state management approach, including setState, BLoC, and more.
  • Layout Agnostic: Provides out-of-the-box widgets for GridView, SliverGrid, ListView, and SliverList layouts, and allows for custom layouts.
  • API Agnostic: Supports any pagination strategy, giving you complete control over API calls.
  • Highly Customizable: Customize the appearance of progress indicators, error messages, and empty lists.
  • Extensible: Easily integrate with pull-to-refresh, filtering, sorting, and more.
  • Status Change Listeners: Not only displays status indicators, but also provides listeners for handling events like errors and empty lists.

Advanced Usage

Customizing Indicators

You can customize the progress, error, and empty list indicators by providing your own widgets to the PagedChildBuilderDelegate:

PagedChildBuilderDelegate(
  itemBuilder: (context, item, index) => BeerListItem(beer: item),
  progressBuilder: (context) => const Center(child: CircularProgressIndicator()),
  firstPageErrorIndicatorBuilder: (context) => const Center(child: Text('Error')),
  firstPageProgressIndicatorBuilder: (context) => const Center(child: CircularProgressIndicator()),
  newPageErrorIndicatorBuilder: (context) => const Center(child: Text('Error')),
  newPageProgressIndicatorBuilder: (context) => const Center(child: CircularProgressIndicator()),
  noItemsFoundIndicatorBuilder: (context) => const Center(child: Text('No Items')),
)

Pull-to-Refresh Integration

To integrate pull-to-refresh, use a RefreshIndicator widget:

RefreshIndicator(
  onRefresh: () async {
    // Refresh the PagingController by calling its refresh() method
    _pagingController.refresh();
  },
  child: PagedListView(...),
)

Filtering and Sorting

You can filter or sort the paginated data by using a StreamController and updating the PagingController with the filtered/sorted results:

// StreamController to listen for filter changes
final filterStreamController = StreamController();

// Update the PagingController with filtered results
filterStreamController.stream.listen((filter) {
  // Filter the data based on the provided filter
  final filteredData = RemoteApi.getBeerList(pageKey, BeerListView._pageSize).where((beer) => beer.name.contains(filter));

  // Update the PagingController with the filtered data
  _pagingController.replace(filteredData);
});

Conclusion

The 'infinite_scroll_pagination' package provides a robust and flexible solution for implementing infinite scroll pagination in Flutter applications. Its unopinionated design, extensibility, and customization options make it an ideal choice for handling pagination scenarios of any complexity.

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