Flutter: How to sent an array to post request API?

Question

I want to send an array for post API in a flutter.

{
    "data":[{"question_id":1,"option_id":2},{"question_id":2,"option_id":6}]
}

I want to send the data like the above.

This is my code:

    class Sent {
      List<Data> data;
    
      Sent({this.data});
    
      Sent.fromJson(Map<String, dynamic> json) {
        if (json['data'] != null) {
          data = new List<Data>();
          json['data'].forEach((v) {
            data.add(new Data.fromJson(v));
          });
        }
      }
    
      Map<String, dynamic> toJson() {
        final Map<String, dynamic> data = new Map<String, dynamic>();
        if (this.data != null) {
          data['data'] = this.data.map((v) => v.toJson()).toList();
        }
        return data;
      }
    }
    
    class Data {
      int questionId;
      int optionId;
    
      Data({this.questionId, this.optionId});
    
      Data.fromJson(Map<String, dynamic> json) {
        questionId = json['question_id'];
        optionId = json['option_id'];
      }
    
      Map<String, dynamic> toJson() {
        final Map<String, dynamic> data = new Map<String, dynamic>();
        data['question_id'] = this.questionId;
        data['option_id'] = this.optionId;
        return data;
      }
    }

Here is how I sent it to POST API

    Future<Sent> saveAnswer() async {

        var data = {"question_id": sent[0][0], "option_id": sent[0][1]};
    
        var url = await Network().link("/exercise/1/saveAnswer");
        SharedPreferences localStorage = await SharedPreferences.getInstance();
        final token = jsonDecode(localStorage.getString('token'));
        http.Response response =
            await http.post(Uri.parse(url), body: jsonEncode(data), headers: {
          'Content-type': 'application/json',
          'Accept': 'application/json',
          'Authorization': 'Bearer $token'
        });
        if (response.statusCode == 200) {
          print(response.body);
        } else {
          print(response.body);
        }
      }

While this is how I get the question_id and option_id from CustomCheckBoxGroup.

List<dynamic> sent;

CustomCheckBoxGroup(
  buttonValuesList: [
    [
      snapshot.data.result[index].id,
      snapshot.data.result[index]
          .options[0].id
    ],
    [
      snapshot.data.result[index].id,
      snapshot.data.result[index]
          .options[1].id
    ],
    [
      snapshot.data.result[index].id,
      snapshot.data.result[index]
          .options[2].id
    ],
    [
      snapshot.data.result[index].id,
      snapshot.data.result[index]
          .options[3].id
    ],
  ],
  checkBoxButtonValues: (values) {
    sent = values;
    print(values);
    print(sent[0][0]);
    print(sent[0][1]);
  },
)

Please help me. How to sent an array like I want to post request API. what is wrong with my code.

Answer 1

I suggest using json.encode

 List<dynamic> ListData = 
 [{"question_id":1,"option_id":2}, 
 {"question_id":2,"option_id":6}];

 var json = {
 'listKey': json.encode(ListData)
 }

Answer 2

Simplest way is to encode the list and add it to json. For example:

List<dynamic> ListData = [{"question_id":1,"option_id":2},{"question_id":2,"option_id":6}];

var json = {
'listKey': json.encode(ListData)
}