Flutter newbie - Fetching data from a JSON file with http

Question

I'm new in this http and JSON world, so I may be wrong on stating or naming some terms. I'm getting a course from Udemy and I'm trying to get a specific object or that object's property. But whatever I do, I'm still fetching all the data, instead of an index.

Here's my code:

import 'dart:convert';
import 'package:flutter/material.dart';
import 'package:http/http.dart';

class JsonParsingSimple extends StatefulWidget {

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

class _JsonParsingSimpleState extends State<JsonParsingSimple> {
  Future data;

  @override
  void initState() {
    // TODO: implement initState
    super.initState();
    data = getData();
  }

{...}

  Future getData() async
  {
    Future data;
    String url = "https://jsonplaceholder.typicode.com/posts";
    Network network = Network(url);

    data = network.fetchData();
    data.then((value)
    {
      print(value[0]['title']); //this line still brings me every data like i'm writing *(value)*
    });
    
    return data; 
  }
}

class Network
{
  final String url;
  Network(this.url);

  Future fetchData() async
  {
    print("$url");
    Response response = await get(Uri.parse(url));

    if(response.statusCode == 200)
    {
      print(response.body);
      return json.decode(response.body); 
    }
    else
    {
      print(response.statusCode);
    }
  }
  
}

print(value) or print(value[0]) or print(value[0]['id']). They're all giving the same. Fetching everything.

Delete print(response.body); If you need 1 post only then you should use: https://jsonplaceholder.typicode.com/posts/<any_ID> instead — Ουιλιαμ Αρκευα
– Ουιλιαμ Αρκευα, Commented Jul 7, 2021 at 15:24
@ΟυιλιαμΑρκευα hahahah you're right. The moment I deleted the print(response.body) line, everything worked fine. Thanks. — boraygen
– boraygen, Commented Jul 7, 2021 at 18:14

Jitesh Mohite · Accepted Answer · 2021-07-07 15:25:57Z

https://jsonplaceholder.typicode.com/posts, providing a list of JSON objects, so basically, we first need to parse them, follow the below example it shows how to create an object and parse it to list.

import 'dart:convert';

import 'package:http/http.dart' as http;

void main() async {
  String url =
      "https://jsonplaceholder.typicode.com/posts";
  final response = await http.get(Uri.parse(url));
  List<JsonData> list = [];
  for(var data in jsonDecode(response.body) as List) {
    list.add(JsonData.fromJson(data));
  }
  print(list[0].id); // Pass the index to get specific values from model
}

class JsonData {
  int? userId;
  int? id;
  String? title;
  String? body;

  JsonData({this.userId, this.id, this.title, this.body});

  JsonData.fromJson(Map<String, dynamic> json) {
    userId = json['userId'];
    id = json['id'];
    title = json['title'];
    body = json['body'];
  }

  Map<String, dynamic> toJson() {
    final Map<String, dynamic> data = new Map<String, dynamic>();
    data['userId'] = this.userId;
    data['id'] = this.id;
    data['title'] = this.title;
    data['body'] = this.body;
    return data;
  }
}

kanwar manraj · Accepted Answer · 2021-07-07 18:03:40Z

The most basic way is to import dart: convert library;

for example, you have data like

{
  "student": {
      "name": "Robin",
      "subject": "computer"
   }
}

import 'dart:convert';

Map<String, dynamic> user = jsonDecode(jsonString);
var name = user['student']['name'];

For simple data the above way is correct, but for more complex data I would recommend using a package or do check it out the below given

You may use this https://app.quicktype.io/ by choosing the language as a dart.
for converting complex JSON data to dart objects. And later using those objects to get the particular value you want

// To parse this JSON data, do
//
//     final welcome = welcomeFromJson(jsonString);

import 'dart:convert';

class Welcome {
    Welcome({
        this.student,
    });

    Student student;

    factory Welcome.fromRawJson(String str) => Welcome.fromJson(json.decode(str));

    String toRawJson() => json.encode(toJson());

    factory Welcome.fromJson(Map<String, dynamic> json) => Welcome(
        student: Student.fromJson(json["student"]),
    );

    Map<String, dynamic> toJson() => {
        "student": student.toJson(),
    };
}

class Student {
    Student({
        this.name,
        this.subject,
    });

    String name;
    String subject;

    factory Student.fromRawJson(String str) => Student.fromJson(json.decode(str));

    String toRawJson() => json.encode(toJson());

    factory Student.fromJson(Map<String, dynamic> json) => Student(
        name: json["name"],
        subject: json["subject"],
    );

    Map<String, dynamic> toJson() => {
        "name": name,
        "subject": subject,
    };
}

The above-given code helps you to convert JSON data to object and vice versa, if you need to send it through an API

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