How to properly handle an array of json in Flutter?

Question

So basically I am getting data from an api using the http package in flutter. The response.body is an array that looks like this:

[
   {
      "id":1,
      "full_name":"Cristiano Ronaldo",
      "avatar":"http://localhost:8000/media/avatars/Ronaldo.jpeg",
      "created":"2021-06-30T02:25:56.332816Z"
   },
   {
      "id":2,
      "full_name":"Paul Pogba",
      "avatar":"http://localhost:8000/media/avatars/Pogba.jpeg",
      "created":"2021-06-30T02:49:17.649970Z"
   },
   {
      "id":3,
      "full_name":"Paulo Dybala",
      "avatar":"http://localhost:8000/media/avatars/Dybala.jpeg",
      "created":"2021-06-30T02:52:33.338296Z"
   },
   {
      "id":4,
      "full_name":"Leonel Messi",
      "avatar":"http://localhost:8000/media/avatars/Messi.jpeg",
      "created":"2021-06-30T02:53:39.539556Z"
   },
   {
      "id":5,
      "full_name":"Kylian Mbappe",
      "avatar":"http://localhost:8000/media/avatars/Mbappe.jpeg",
      "created":"2021-06-30T02:57:29.891686Z"
   }
]

My problem is I want to essentially format this into the "dart" way. Something like this:

List players = response.body;

The error I'm getting is this:

A value of type 'String' can't be assigned to a variable of type 'List<dynamic>'.
Try changing the type of the variable, or casting the right-hand type to 'List<dynamic>'.

Why is this error occurring. I know the list is already properly formatted and the key-value pairs of the json objects are all strings but I would like to format it into the "dart" way. If I do this:

var players = response.body;

It does work. Should I just use var and call it good or should I format it?

Side Question: If I wanted to call the method to get the data from the api in the initState method, would I do:

Future<void> _getPlayers() async {
   ...
} 

void initState() {
   super.initState();
   _getPlayers();
}

Thank You!

Kishan Dhankecha · Accepted Answer · 2021-06-30 06:41:34Z

9

There are many ways you can do this

Most efficient way is to Make a `Object` like this

class Player {
  final int id;
  final String fullName;
  final String avatar;
  final String created;

  const Player({this.id, this.fullName, this.avatar, this.created});

  Player.fromJson(Map<String, dynamic> json) {
    id = json['id'];
    fullName = json['full_name'];
    avatar = json['avatar'];
    created = json['created'];
  }

  Map<String, dynamic> toJson() {
    final Map<String, dynamic> data = new Map<String, dynamic>();
    data['id'] = this.id;
    data['full_name'] = this.fullName;
    data['avatar'] = this.avatar;
    data['created'] = this.created;
    return data;
  }
}

Then You can add value

Instead of like this

List players = response.body

You can use like this

var data = json.decode(response.body);

List<Player> players  = data.map((element){
   return Player.fromJson(element);
}).toList();

For access data from `players` list

You can do like this

players[0].fullName;
players[1].fullName;

edited Jun 30, 2021 at 6:41

answered Jun 30, 2021 at 6:38

Kishan Dhankecha

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3 Comments

darkstar Over a year ago

Hey I'm fairly new to flutter so I'm not too good with it. Why is your solution the way it is? Like the answer I accepted was super simple and it worked but I've seen many people do it like this as well. Why is this the best/correct way?

Kishan Dhankecha Over a year ago

By creating a custom Dart class for our API responses is very useful as we know what kind of data our variable accepts from API and also We can add testing rules easily to the custom class. FOR BEGINNER LEVEL - The custom class helps to check if the data coming from API is right and perfect as we needed. This helps in unwanted app crashes or errors. Hope you got my point.

Kishan Dhankecha Over a year ago

List players = jsonDecode(response.body); in this scenario you are not sure what data your players List will have. If response.body returns unwanted data your List of players will also get the wrong data. So this will directly affect the point where you are displaying the data from players List. Creating the custom class will help to check data coming from response.body before assigning to the players List.

Sajad Abdollahi · Accepted Answer · 2021-06-30 06:44:06Z

2

Basically, you are trying to cast a JSON to list without decoding it,

an encoded JSON is a String like this

"{ \"username\": \"ali\", \"number\": \"[email protected]\" }"

and when you decode it, it becomes a List or a Map like this

{ 
   "username": "ali",
   "email": "[email protected]"
}

So to fix your code you need to decode the json and then cast it to a list

List players = jsonDecode(response.body);

...

Side Answer :

Yes you can do that but that will cause an exceptions while navigating between pages (imagine you sent a request to the server and when data comes you have to setState the widget but even when the widget disposes and you navigated to other pages, your method will call setState on an unmounted widget and it will cause exception)

So if you are not planning on using dependency management libraries then just use future builder

edited Jun 30, 2021 at 6:44

answered Jun 30, 2021 at 6:37

Sajad Abdollahi

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1 Comment

Nagual Over a year ago

this is definitely NOT the best answer

The Anonymous Koder · Accepted Answer · 2021-06-30 06:37:02Z

1

add this to your code:

import 'dart:convert';

then,

var players = jsonDecode(response.body);

answered Jun 30, 2021 at 6:37

The Anonymous Koder

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How to properly handle an array of json in Flutter?

3 Answers 3

There are many ways you can do this

Most efficient way is to Make a `Object` like this

Then You can add value

For access data from `players` list

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Collectives™ on Stack Overflow

3 Answers 3

There are many ways you can do this

Most efficient way is to Make a Object like this

Then You can add value

For access data from players list

3 Comments

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Most efficient way is to Make a `Object` like this

For access data from `players` list