How to decode JSON in Flutter?

How to decode JSON in Flutter?

The question is simple, but the answer isn't, at least for me.

I have a project that uses a lot of JSON Strings. Basically, the entire communication between the app and the server is through JSON.

I have been using JSON.decode(json_string) to deal with it, but today I updated the Flutter core (0.5.8-pre.178) and JSON.decode isn't available anymore.

I went to the Flutter Docs to seek help, but it still says to use JSON.decode.

So, how to decode JSON in Flutter from now on?

Solution 1:

You will need to import dart:convert:

import 'dart:convert';

Inline example

String rawJson = '{"name":"Mary","age":30}';

Map<String, dynamic> map = jsonDecode(rawJson); // import 'dart:convert';

String name = map['name'];
int age = map['age'];

Person person = Person(name, age);

Note: When I was doing this in VS Code for server side Dart I had to specify the type:

Map<String, dynamic> map = jsonDecode(rawJson) as Map<String, dynamic>;

Model class example

The model class includes the map conversion logic:

class Person {
  String name;
  int age;
  Person(this.name, this.age);

  // named constructor
  Person.fromJson(Map<String, dynamic> json)
      : name = json['name'],
        age = json['age'];

  // method
  Map<String, dynamic> toJson() {
    return {
      'name': name,
      'age': age,
    };
  }
 
}

And the JSON conversion is done like this:

String rawJson = '{"name":"Mary","age":30}';
Map<String, dynamic> map = jsonDecode(rawJson);
Person person = Person.fromJson(map);

See my full answer here.

Generating the serialization code

It is easy to make errors when writing the serialization code, so it is generally recommended to use the json_serializable package by the Dart Team. However, you can read about the pros and cons of the different methods here.

If you want even more options you can also check out the built_value package.

See also

• Work with JSON in Flutter - Part 1: dart:convert
• Work with JSON in Flutter - Part 2: json_serializable
• Some Options for Deserializing JSON with Flutter

Solution 2:

Just use

json.decode()

or

jsonDecode()

In Dart 2 all screaming-case constants were changed to lower-camel-case.

Ensure to import 'dart:convert';