Flutter - how to parse paged JSON data into ListView?

Question

I am trying to parse JSON data into a Listview when using a searchview. I currently have it working, my issue is the data from my url is paginated . When I just do one set of data, it is no problem, but I can't figure out how to do multiple data. I have tried a for loop to run through all the pages but I can not put it into my response to pull the data. Basically I want to run through all the paged urls, and then get the response data from the entire list of urls. Not sure how to achieve this. Any help?

Portion of code w/ For Loop

Future<List<Coins>> fetchList() async {

for (i = 0; i < 25; i++){
url = 'www.example.com/page=$i';
}

var response = await http.get(url);

var coins = List<Coins>();

if (response.statusCode == 200) {
  var coinsJSON = json.decode(response.body);
  for (var coinJSON in coinsJSON) {
    coins.add(Coins.fromJson(coinJSON));
  }
}
return coins;
}

Full Class Code

class SearchBar extends SearchDelegate<String> {
List<Coins> _coins = List<Coins>();

Future<List<Coins>> fetchList() async {
var url = 'www.example.com/page=1';
var response = await http.get(url);

var coins = List<Coins>();

if (response.statusCode == 200) {
  var coinsJSON = json.decode(response.body);
  for (var coinJSON in coinsJSON) {
    coins.add(Coins.fromJson(coinJSON));
  }
}
return coins;
}

@override
Widget buildSuggestions(BuildContext context) {
// What to display while searching
SearchBar().fetchList().then((value) {
  _coins.clear();
  _coins.addAll(value);
});


final suggestionList = query.isEmpty ? 
[]:_coins.where((item)=>item.name.toLowerCase().startsWith(query.toLowerCase())).toList();

return ListView.builder(
    itemCount: suggestionList.length,
    itemBuilder: (context, index) {
      return ListTile(
        title: Text(suggestionList[index].name),
      );
    });
}
}

Answer 1

You can use package https://pub.dev/packages/incrementally_loading_listview
it can load data by page, you can set number per page and control when to load more data with _loadingMore function

In your case, in _loadMoreItems(), you can call api for next page and add to items list

code snippet

  bool _loadingMore;
  bool _hasMoreItems;
  int _maxItems = 30;
  int _numItemsPage = 10;
  Future _initialLoad;

  Future _loadMoreItems() async {
    final totalItems = items.length;
    await Future.delayed(Duration(seconds: 3), () {
      for (var i = 0; i < _numItemsPage; i++) {
        items.add(Item('Item ${totalItems + i + 1}'));
      }
    });

    _hasMoreItems = items.length < _maxItems;
  }

full code

import 'dart:async';

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

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

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  // This widget is the home page of your application. It is stateful, meaning
  // that it has a State object (defined below) that contains fields that affect
  // how it looks.

  // This class is the configuration for the state. It holds the values (in this
  // case the title) provided by the parent (in this case the App widget) and
  // used by the build method of the State. Fields in a Widget subclass are
  // always marked "final".

  final String title;

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

class _MyHomePageState extends State<MyHomePage> {
  List<Item> items;
  bool _loadingMore;
  bool _hasMoreItems;
  int _maxItems = 30;
  int _numItemsPage = 10;
  Future _initialLoad;

  Future _loadMoreItems() async {
    final totalItems = items.length;
    await Future.delayed(Duration(seconds: 3), () {
      for (var i = 0; i < _numItemsPage; i++) {
        items.add(Item('Item ${totalItems + i + 1}'));
      }
    });

    _hasMoreItems = items.length < _maxItems;
  }

  @override
  void initState() {
    super.initState();
    _initialLoad = Future.delayed(Duration(seconds: 3), () {
      items = List<Item>();
      for (var i = 0; i < _numItemsPage; i++) {
        items.add(Item('Item ${i + 1}'));
      }
      _hasMoreItems = true;
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      backgroundColor: Colors.yellow,
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: FutureBuilder(
          future: _initialLoad,
          builder: (context, snapshot) {
            switch (snapshot.connectionState) {
              case ConnectionState.waiting:
                return Center(child: CircularProgressIndicator());
              case ConnectionState.done:
                return IncrementallyLoadingListView(
                  hasMore: () => _hasMoreItems,
                  itemCount: () => items.length,
                  loadMore: () async {
                    // can shorten to "loadMore: _loadMoreItems" but this syntax is used to demonstrate that
                    // functions with parameters can also be invoked if needed
                    await _loadMoreItems();
                  },
                  onLoadMore: () {
                    setState(() {
                      _loadingMore = true;
                    });
                  },
                  onLoadMoreFinished: () {
                    setState(() {
                      _loadingMore = false;
                    });
                  },
                  loadMoreOffsetFromBottom: 2,
                  itemBuilder: (context, index) {
                    final item = items[index];
                    if ((_loadingMore ?? false) && index == items.length - 1) {
                      return Column(
                        children: <Widget>[
                          ItemCard(item: item),
                          Card(
                            child: Padding(
                              padding: const EdgeInsets.all(16.0),
                              child: Column(
                                children: <Widget>[
                                  Row(
                                    crossAxisAlignment:
                                    CrossAxisAlignment.start,
                                    children: <Widget>[
                                      Container(
                                        width: 60.0,
                                        height: 60.0,
                                        color: Colors.grey,
                                      ),
                                      Padding(
                                        padding: const EdgeInsets.fromLTRB(
                                            8.0, 0.0, 0.0, 0.0),
                                        child: Container(
                                          color: Colors.grey,
                                          child: Text(
                                            item.name,
                                            style: TextStyle(
                                                color: Colors.transparent),
                                          ),
                                        ),
                                      )
                                    ],
                                  ),
                                  Padding(
                                    padding: const EdgeInsets.fromLTRB(
                                        0.0, 8.0, 0.0, 0.0),
                                    child: Container(
                                      color: Colors.grey,
                                      child: Text(
                                        item.message,
                                        style: TextStyle(
                                            color: Colors.transparent),
                                      ),
                                    ),
                                  )
                                ],
                              ),
                            ),
                          ),
                        ],
                      );
                    }
                    return ItemCard(item: item);
                  },
                );
              default:
                return Text('Something went wrong');
            }
          }),
    );
  }
}

class ItemCard extends StatelessWidget {
  const ItemCard({
    Key key,
    @required this.item,
  }) : super(key: key);

  final Item item;

  @override
  Widget build(BuildContext context) {
    return GestureDetector(
      child: Card(
        child: Padding(
          padding: const EdgeInsets.all(16.0),
          child: Column(
            children: <Widget>[
              Row(
                crossAxisAlignment: CrossAxisAlignment.start,
                children: <Widget>[
                  Image.network(item.avatarUrl),
                  Expanded(
                    child: Padding(
                      padding: const EdgeInsets.fromLTRB(8.0, 0.0, 0.0, 0.0),
                      child: Text(item.name),
                    ),
                  )
                ],
              ),
              Padding(
                padding: const EdgeInsets.fromLTRB(0.0, 8.0, 0.0, 0.0),
                child: Text(item.message),
              )
            ],
          ),
        ),
      ),
      onTap: () => Navigator.of(context).push(
        MaterialPageRoute(builder: (context) => ItemDetailsPage(item)),
      ),
    );
  }
}

class ItemDetailsPage extends StatelessWidget {
  final Item item;
  const ItemDetailsPage(this.item);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
        backgroundColor: Colors.yellow,
        appBar: AppBar(
          title: Text(item.name),
        ),
        body: Container(
          child: Text(item.message),
        ));
  }
}

class Item {
  final String name;
  final String avatarUrl = 'http://via.placeholder.com/60x60';
  final String message =
      'Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.';

  Item(this.name);
}