I'm trying to write json data from a third-party site on a flater, but I've already tried different options. I get the same problem on the last step. Please help me very much.

i have this model

class SkinModel {
  String src;
  String name;
  double minprice;
  int count;
  double avgprice;
  double medianprice;
  int popularity;

  SkinModel(
      {required this.src,
      required this.name,
      required this.minprice,
      required this.count,
      required this.avgprice,
      required this.medianprice,
      required this.popularity});

  factory SkinModel.fromJson(Map<String, dynamic> json) {
    return SkinModel(
      src: json['src'],
      name: json['name'],
      minprice: json['minprice'],
      count: json['count'],
      avgprice: json['avgprice'],
      medianprice: json['medianprice'],
      popularity: json['popularity'],
    );
  }
}

and such a class for receiving and processing data

import 'dart:convert';

import 'package:flutter_application_1/data_skins.dart';
import 'package:flutter_application_1/model/model_skin.dart';
import 'package:http/http.dart' as http;

class Skins {
  Future<dynamic>? getSkinsPopular(String game, String? method) async {
    late List<SkinModel> skinListModel = [];
    if (method == null) {
      skinListModel = skinssamplelist;
    }

    String url = 'https://market.dota2.net/api/v2/prices/USD.json';
    print('Step 1 '   url);

    http.Response response = await http.get(
      Uri.parse(url),
    );
    print('Step 2 '   response.reasonPhrase!);
    if (response.statusCode == 200) {
      var decodeData = json.decode(response.body);
      var rest = decodeData['items'] as List;
      print('Step 3');
      print(rest);
      skinListModel =
          rest.map<SkinModel>((json) => SkinModel.fromJson(json)).toList();
      print('Step 4');
      print(skinListModel);

    } else {
      throw 'Problem with get request';
    }

    return skinListModel;
  }
}
}

But the last successful step 3 and after the debugger writes flutter: Sorry try again I absolutely do not understand what the error is and what I did wrong

CodePudding user response：

 late List<SkinModel> skinListModel = [];
  String url = 'https://market.dota2.net/api/v2/prices/USD.json';
  print('Step 1 '   url);

  http.Response response = await http.get(
    Uri.parse(url),
  );
  print('Step 2 '   response.reasonPhrase!);
  if (response.statusCode == 200) {
    var decodeData = jsonDecode(response.body);
    var rest = decodeData['items'] as List;
    print('Step 3');
    print(rest);
    for (var element in rest) {skinListModel.add(SkinModel.fromJson(element)); } //replace this line
    print('Step 4');
    print(skinListModel);

  } else {
    throw 'Problem with get request';
  }

CodePudding user response：

You are trying to send a request to https://market.dota2.net/api/v2/prices/USD.json and it returns items array of object. Object has fields:

market_hash_name: String,
volume: String,
price: String,

In your code you are trying to parse the json, but your SkinModel has these fields:

String src;
String name;
double minprice;
int count;
double avgprice;
double medianprice;
int popularity;

While converting json to your SkinModel, you try to get values from fields that don't exist. The error occurs in this line.

src: json['src'], // You try to get src but it does not exist

Flutter says that you cannot transform null to String.

_TypeError (type 'Null' is not a subtype of type 'String')

In order to fix error, use another api url. Or change your model to this:

class SkinModel {
  final String market_hash_name;
  final String volume;
  final String price;
}