Lernen Pagination and Infinite Lists

Definition

Pagination is a technique that lets you load large sets of data in smaller, manageable chunks.

In Flutter, infinite scrolling is a common way to implement pagination, where more data is fetched as the user reaches the end of a scrollable list. This approach keeps your app responsive and efficient, especially when working with remote APIs that return long lists of items.

main.dart


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import 'package:flutter/material.dart';

void main() => runApp(PaginatedListApp());

class PaginatedListApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: PaginatedListScreen(),
    );
  }
}

class PaginatedListScreen extends StatefulWidget {
  @override
  _PaginatedListScreenState createState() => _PaginatedListScreenState();
}

class _PaginatedListScreenState extends State<PaginatedListScreen> {
  final ScrollController _controller = ScrollController();
  final List<int> _items = [];
  bool _isLoading = false;
  bool _hasMore = true;
  int _page = 0;
  final int _limit = 20;

  @override
  void initState() {
    super.initState();
    _fetchItems();
    _controller.addListener(() {
      if (_controller.position.pixels >= _controller.position.maxScrollExtent - 200 && !_isLoading && _hasMore) {
        _fetchItems();
      }
    });
  }

  Future<void> _fetchItems() async {
    setState(() {
      _isLoading = true;
    });

    // Simulate API call delay
    await Future.delayed(Duration(seconds: 2));

    // Simulate API response
    List<int> fetched = List.generate(_limit, (i) => _page * _limit + i);

    setState(() {
      _items.addAll(fetched);
      _isLoading = false;
      _page++;
      if (fetched.length < _limit) {
        _hasMore = false;
      }
    });
  }

  @override
  void dispose() {
    _controller.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text('Paginated List')),
      body: ListView.builder(
        controller: _controller,
        itemCount: _items.length + (_hasMore ? 1 : 0),
        itemBuilder: (context, index) {
          if (index < _items.length) {
            return ListTile(title: Text('Item [${_items[index]}'));
          } else {
            return Padding(
              padding: const EdgeInsets.symmetric(vertical: 16.0),
              child: Center(child: CircularProgressIndicator()),
            );
          }
        },
      ),
    );
  }
}

Scroll controllers allow you to listen for scroll events and determine when the user is near the end of a list. In the paginated list example, a ScrollController is used to trigger the loading of more items as the user scrolls close to the bottom. A loading indicator, such as CircularProgressIndicator, is displayed at the end of the list while new data is being fetched. This provides clear feedback and ensures a smooth user experience during incremental data loading.

main.dart


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void main() {
  List<String> currentItems = ['Apple', 'Banana', 'Cherry'];
  List<String> newItems = ['Date', 'Elderberry'];

  // Append newItems to currentItems
  currentItems.addAll(newItems);

  print(currentItems); // Output: [Apple, Banana, Cherry, Date, Elderberry]
}

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Abschnitt 2. Kapitel 4

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Definition

Pagination is a technique that lets you load large sets of data in smaller, manageable chunks.

main.dart


              12345678910111213141516171819202122232425262728293031323334353637383940414243444546474849505152535455565758596061626364656667686970717273747576777879808182838485
            
import 'package:flutter/material.dart';

void main() => runApp(PaginatedListApp());

class PaginatedListApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: PaginatedListScreen(),
    );
  }
}

class PaginatedListScreen extends StatefulWidget {
  @override
  _PaginatedListScreenState createState() => _PaginatedListScreenState();
}

class _PaginatedListScreenState extends State<PaginatedListScreen> {
  final ScrollController _controller = ScrollController();
  final List<int> _items = [];
  bool _isLoading = false;
  bool _hasMore = true;
  int _page = 0;
  final int _limit = 20;

  @override
  void initState() {
    super.initState();
    _fetchItems();
    _controller.addListener(() {
      if (_controller.position.pixels >= _controller.position.maxScrollExtent - 200 && !_isLoading && _hasMore) {
        _fetchItems();
      }
    });
  }

  Future<void> _fetchItems() async {
    setState(() {
      _isLoading = true;
    });

    // Simulate API call delay
    await Future.delayed(Duration(seconds: 2));

    // Simulate API response
    List<int> fetched = List.generate(_limit, (i) => _page * _limit + i);

    setState(() {
      _items.addAll(fetched);
      _isLoading = false;
      _page++;
      if (fetched.length < _limit) {
        _hasMore = false;
      }
    });
  }

  @override
  void dispose() {
    _controller.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text('Paginated List')),
      body: ListView.builder(
        controller: _controller,
        itemCount: _items.length + (_hasMore ? 1 : 0),
        itemBuilder: (context, index) {
          if (index < _items.length) {
            return ListTile(title: Text('Item [${_items[index]}'));
          } else {
            return Padding(
              padding: const EdgeInsets.symmetric(vertical: 16.0),
              child: Center(child: CircularProgressIndicator()),
            );
          }
        },
      ),
    );
  }
}

main.dart


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void main() {
  List<String> currentItems = ['Apple', 'Banana', 'Cherry'];
  List<String> newItems = ['Date', 'Elderberry'];

  // Append newItems to currentItems
  currentItems.addAll(newItems);

  print(currentItems); // Output: [Apple, Banana, Cherry, Date, Elderberry]
}

War alles klar?

Danke für Ihr Feedback!

Abschnitt 2. Kapitel 4