so It's my first time using API on flutter I just take the tutorial copy paste and change some line for the test I just want to learn more about API's so don't blame me if I made a dumb mistake or something like . I try to get a title from the APi and get this error if somoene can help that will be really great.

Future<Album> fetchAlbum() async {
  final response = await http
      .get(Uri.parse('https://api.mangadex.org/manga'));

  if (response.statusCode == 200) {
    return Album.fromJson(jsonDecode(response.body));
  } else {

    throw Exception('Failed to load album');
  }
}

class Album {

  final int year;
  final String title;

  const Album({

    required this.year,
    required this.title,
  });

  factory Album.fromJson(Map<String, dynamic> json) {
    return Album(
      year: json['year'],
      title: json['title'],
    );
  }
}

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

class MyApp extends StatefulWidget {
  const MyApp({Key? key}) : super(key: key);

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

class _MyAppState extends State<MyApp> {
  late Future<Album> futureAlbum;

  @override
  void initState() {
    super.initState();
    futureAlbum = fetchAlbum();

  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Fetch Data Example',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: Scaffold(
        appBar: AppBar(
          title: const Text('Fetch Data Example'),
        ),
        body: Center(
          child: FutureBuilder<Album>(
            future: futureAlbum,
            builder: (context, snapshot) {
              if (snapshot.hasData) {
                return Text(snapshot.data!.title);
              } else if (snapshot.hasError) {
                return Text('${snapshot.error}');
              }
              return const CircularProgressIndicator();

CodePudding user response：

actually what goes wrong here is that json response you are getting back from the API doesn't contain a year or title fields. So, both json['year'] and json['title'] will be null. And since you are assigning them to Album.year and Album.title which are not nullable, the whole app breaks.

I tried calling the API URI, and found that the JSON structure is a bit different.

You might wan this code for your fromJson method for it to work.

factory Album.fromJson(Map<String, dynamic> json) {
  return Album(
    year: json['data'][0]['attributes']['year'],
    title: json['data'][0]['attributes']['title']["en"],
  );
}

Please note that json['data'] is actually an array of albums, in this code we're just fetching ONLY the first element inside that array.

CodePudding user response：

If I understand what you're going for, you should call fetchAlbum() instead of using futureAlbum in the FutureBuilder since the fetchAlbum() method is a Future that returns the album info. The call of futureAlbum = fetchAlbum() in initState doesn't fetch the album info in a manner that's useable, there's a way to do it, but it's complicated and not needed since you're already using the FutureBuilder.