JSON API with Flutter is not fetching data

Question

I have a problem fetching data from a json api. I have this structure:

{
    "team": {
        "team_name": "Team Name",
        "team_quantity": 10,
        "team_victory": 2,
    }
}

and I'm trying to fetch data with Flutter:

class Team{
 final String name;
 final int quantity;
 final int victory;

  Team({this.name, this.quantity, this.victory});

  factory Team.fromJson(Map<String, dynamic> json){
    return Team(
      name: json['team_name'] as String,
      quantity: json['team_quantity'] as int,
      victory: json['team_victory'] as int,
    );
  }
}

Future<List<Team>> fetchTeam(http.Client client) async {
  final response =
      await http.get('url');
  return compute(parseTeam, response.body);
}

List<Team> parseTeam(String responseBody) {
  final parsed = jsonDecode(responseBody).cast<Map<String, dynamic>>();

  return parsed.map<Team>((json) => Team.fromJson(json)).toList();
}

I get this error:

I/flutter (25834): Exception: NoSuchMethodError: Class '_InternalLinkedHashMap<String, dynamic>' has no instance method 'cast' with matching arguments.
I/flutter (25834): Receiver: _LinkedHashMap len:1
I/flutter (25834): Tried calling: cast<Map<String, dynamic>>()
I/flutter (25834): Found: cast<RK, RV>() => Map<RK, RV>

Could you explain the error(s) to me? Thanks so much!

Maybe my problem could be the "team" in the api? I will try fetching data with the same structure in Flutter:

{
    "team": {
        "team_name": "Team Name",
        "team_quantity": 10,
        "team_victory": 2,
    }
}

or

{
   "team_name": "Team Name",
   "team_quantity": 10,
   "team_victory": 2,
}

MickaelHrndz · Accepted Answer · 2021-01-09 09:45:50Z

1

try replacing

final parsed = jsonDecode(responseBody).cast<Map<String, dynamic>>();

with

final Map<String, dynamic> parsed = jsonDecode(responseBody);

answered Jan 9, 2021 at 9:45

MickaelHrndz

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9 Comments

DarkKey964 Over a year ago

i already seen it, but doesn't work for me... the problem could be the "team:{...}" ? I will edit the question with an exmple (thanks for the reply!)

MickaelHrndz Over a year ago

Is it throwing the same error when you make the change ?

DarkKey964 Over a year ago

yes, i edited the main post if you want help me... I don't understand how can i modify my structure

MickaelHrndz Over a year ago

I tested my solution with your code and json, and it solves the error. Maybe you have the same error somewhere else ? Also, is your Flutter up-to-date ? If not, run flutter upgrade.

DarkKey964 Over a year ago

i don't know how to return with the new parsed. How can i change the return: return parsed.map<Team>((json) => Team.fromJson(json)).toList();

|

Hakkı Akut · Accepted Answer · 2021-01-11 20:53:22Z

0

Your code seems fine just use this

{
   "team_name": "Team Name",
   "team_quantity": 10,
   "team_victory": 2,
}

also make sure you have these imports

import 'dart:async' show Future;
import 'package:flutter/foundation.dart';
import 'package:http/http.dart' as http;
import 'dart:convert';

if you want use with Teams then wrap teams with another class like league

 class League {
 List<Team> teams;
League({this.teams});
factory League.fromJson(Map<String, dynamic> json,) {
    if (json["team"] != null) {
      var teams1= json["team"] as List;
      List<Team> _teams=
      teams1.map((list) => Team.fromJson(list)).toList();
      return League(
        teams: _teams,
      );
    }
    return null;
  }
}

and this is how you fetch data

Future<League> getLeague() async {
  final response = await http.Client().get('$url');
  if (response.statusCode == 200) {
    return League.fromJson(json.decode(response.body));
  }
  return null;
}

edited Jan 11, 2021 at 20:53

answered Jan 9, 2021 at 11:03

Hakkı Akut

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4 Comments

DarkKey964 Over a year ago

Thanks for the reply, i can't use this, i can use only the first with "team", how can i modify the code to fetch data in this case

DarkKey964 Over a year ago

Don't work for me... where you use the "teams1" variable? Did you test it? Thanks again for the help

Hakkı Akut Over a year ago

sorry about that i editted again. this must work imo.

DarkKey964 Over a year ago

oh ok perfect, i get always the same error... this part is correct? Future<List<League>> fetchLeague(http.Client client) async { final response = await http.get('url'); return compute(parseLeague, response.body); } List<League> parseLeague(String responseBody) { final parsed = jsonDecode(responseBody).cast<Map<String, dynamic>>(); return parsed.map<League>((json) => League.fromJson(json)).toList(); }

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