How to Deserialize a list of objects from json in flutter

Question

I am using the dart package json_serializable for json serialization. Looking at the flutter documentation it shows how to deserialize a single object as follow:

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Answer 1

Well, your service would handle either the response body being a map, or a list of maps accordingly. Based on the code you have, you are accounting for 1 item.

If the response body is iterable, then you need to parse and walk accordingly, if I am understanding your question correctly.

Example:

Iterable l = json.decode(response.body);
List<Post> posts = List<Post>.from(l).map((Map model)=> Post.fromJson(model)).toList();

where the post is a LIST of posts.

EDIT: I wanted to add a note of clarity here. The purpose here is that you decode the response returned. The next step, is to turn that iterable of JSON objects into an instance of your object. This is done by creating fromJson methods in your class to properly take JSON and implement it accordingly. Below is a sample implementation.

class Post {
  // Other functions and properties relevant to the class
  // ......
  /// Json is a Map<dynamic,dynamic> if i recall correctly.
  static fromJson(json): Post {
    Post p = new Post()
    p.name = ...
    return p
  }
}

I am a bit abstracted from Dart these days in favor of a better utility for the tasks needing to be accomplished. So my syntax is likely off just a little, but this is Pseudocode.

Edit There was a change in the API for this functionality at some point in the past. I do not program in Dart anymore so it is hard for me to test some of these updates. That being said, it looks like it is having issues casting now in this newer version of the dart, and I updated the above answer. It takes the iterable and casts it to a List of Post, and then will conduct a map on that List.

Answer 2

Just another example on JSON Parsing for further clarification.

Let say we want to parse items array in our JSON Object.

factory YoutubeResponse.fromJSON(Map<String, dynamic> YoutubeResponseJson) 
 {

// Below 2 line code is parsing JSON Array of items in our JSON Object (YouttubeResponse)


var list = YoutubeResponseJson['items'] as List;
List<Item> itemsList = list.map((i) => Item.fromJSON(i)).toList();

return new YoutubeResponse(
    kind: YoutubeResponseJson['kind'],
    etag: YoutubeResponseJson['etag'],
    nextPageToken: YoutubeResponseJson['nextPageToken'],
    regionCode: YoutubeResponseJson['regionCode'],
    mPageInfo: pageInfo.fromJSON(YoutubeResponseJson['pageInfo']),

    // Here we are returning parsed JSON Array.

    items: itemsList);

  }

Answer 3

First, create a class that matches your json data, in my case, I create (generate) class named Img:

import 'dart:convert';

Img imgFromJson(String str) => Img.fromJson(json.decode(str));
String imgToJson(Img data) => json.encode(data.toJson());

class Img {
    String id;
    String img;
    dynamic decreption;

    Img({
        this.id,
        this.img,
        this.decreption,
    });

    factory Img.fromJson(Map<String, dynamic> json) => Img(
        id: json["id"],
        img: json["img"],
        decreption: json["decreption"],
    );

    Map<String, dynamic> toJson() => {
        "id": id,
        "img": img,
        "decreption": decreption,
    };
}

PS. You can use app.quicktype.io to generate your json data class in dart. then send you post/get to your server:

Future<List<Img>> _getimages() async {
    var response = await http.get("http://192.168.115.2/flutter/get_images.php");
    var rb = response.body;

    // store json data into list
    var list = json.decode(rb) as List;

    // iterate over the list and map each object in list to Img by calling Img.fromJson
    List<Img> imgs = list.map((i)=>Img.fromJson(i)).toList();

    print(imgs.runtimeType); //returns List<Img>
    print(imgs[0].runtimeType); //returns Img

    return imgs;
}

for more info this is an article about Parsing complex JSON in Flutter

Answer 4

follow this step
step 1-> create model class (name as LoginResponce ) click here to convert json to dart .
step 2-> LoginResponce loginResponce=LoginResponce.fromJson(json.decode(response.body));

step 3 -> now you get your data in instence of model (as loginResponce ).

Answer 5

For example, every item in the array is a JSON object.

{
  "tags": [
    {
      "name": "dart",
      "quantity": 12
    },
    {
      "name": "flutter",
      "quantity": 25
    },
    {
      "name": "json",
      "quantity": 8
    }
  ]
}

We will need a class that represents the Tag item. So we create Tag class with 2 fields like this.

class Tag {
  String name;
  int quantity;

  Tag(this.name, this.quantity);

  factory Tag.fromJson(dynamic json) {
    return Tag(json['name'] as String, json['quantity'] as int);
  }

  @override
  String toString() {
    return '{ ${this.name}, ${this.quantity} }';
  }
}

The method factory Tag.fromJson(dynamic json) will parse a dynamic object into a Tag object. We will need it in the main() function, at the mapping step.

import 'dart:convert';

main() {
  String arrayObjsText =
      '{"tags": [{"name": "dart", "quantity": 12}, {"name": "flutter", "quantity": 25}, {"name": "json", "quantity": 8}]}';

  var tagObjsJson = jsonDecode(arrayObjsText)['tags'] as List;
  List<Tag> tagObjs = tagObjsJson.map((tagJson) => Tag.fromJson(tagJson)).toList();

  print(tagObjs);
}

Let me explain the code above. It’s simple. – jsonDecode() convert the 'tags' JSON object into a dynamic object. Then we use brackets ['tags'] to get JSON array inside it. – as List returns a List<dynamic> that we will use map() to change every dynamic item of the List into Tag object. – Finally, .toList() convert the Iterable result above into List<Tag> object.

Now, if we run the code, the result will be like this.

[{ dart, 12 }, { flutter, 25 }, { json, 8 }]

Answer 6

I always use this way with no problem;

List<MyModel> myModels;
var response = await http.get("myUrl");

myModels=(json.decode(response.body) as List).map((i) =>
              MyModel.fromJson(i)).toList();