Parsing JSON that has a nested array of objects in Dart?

Try genres = (jsonMap['genres'] as List).map((i) => Genre.fromJson(i)).toList()

The issue: calling map without the cast makes it a dynamic call, which means the return type from Genre.fromJson is also dynamic (not Genre).

Take a look at https://flutter.io/json/ for some hints.

There are solutions, like https://pub.dartlang.org/packages/json_serializable, that makes this much easier

After receiving the response, first of all, you need to extract the arrays separately. Then you can easily map. This is the way I do it.

List<Attempts> attempts;
attempts=(jsonDecode(res.body)['message1'] as List).map((i) => Attempts.fromJson(i)).toList();
List<Posts> posts;
attempts=(jsonDecode(res.body)['message2'] as List).map((i) => Post.fromJson(i)).toList();

Refer below example.

   Future<List<Attempts>> getStatisticData() async {
    String uri = global.serverDNS + "PaperAttemptsManager.php";
    var res = await http.post(
      uri,
      headers: <String, String>{
        'Content-Type': 'application/json; charset=UTF-8',
      },
      body: jsonEncode(<String, String>{
        'userName': widget.userId,
        'subject': widget.subjectName,
        'method': "GETPTEN",
      }),
    );

    if (res.statusCode == 200) {
      List<Attempts> attempts;
      attempts=(jsonDecode(res.body)['message'] as List).map((i) => Attempts.fromJson(i)).toList();
      return attempts;
    } else {
      throw "Can't get subjects.";
    }
  }

Model Class

class Attempts {
  String message, userName, date, year, time;
  int status, id, marks, correctAnswers, wrongAnswers, emptyAnswers;

  Attempts({
    this.status,
    this.message,
    this.id,
    this.userName,
    this.date,
    this.year,
    this.marks,
    this.time,
    this.correctAnswers,
    this.wrongAnswers,
    this.emptyAnswers,
  });

  factory Attempts.fromJson(Map<String, dynamic> json) {
    return Attempts(
      status: json['status'],
      message: json['message'],
      id: json['ID'],
      userName: json['USERNAME'],
      date: json['DATE'],
      year: json['YEAR'],
      marks: json['MARKS'],
      time: json['TIME'],
      correctAnswers: json['CORRECT_ANSWERS'],
      wrongAnswers: json['WRONG_ANSWERS'],
      emptyAnswers: json['EMPTY_ANSWERS'],
    );
  }
}

I think JSONtoDart Converter is very useful, Must try...