JSON conversion in Flutter and Dart

A quick reference with examples

Article updated July 4, 2023 for Dart 3.

The article Parsing Complex JSON in Flutter is very good, but I was looking for something shorter, a quick reference with examples.

If I have a simple JSON string like this:

{
    "name" : "Mary",
    "age" : 30
}

How do I convert it to a Dart object? Or a Dart object to JSON?

Setup

Import the builtin convert library, which includes the jsonDecode() and jsonEncode() methods:

import 'dart:convert';

I will use the class below in the following examples:

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

And while it isn’t absolutely necessary, I’m also using the strict typing rules in analysis_options.yaml. This lets the analyzer warn you when you might forget about dynamic and object types.

include: package:lints/recommended.yaml

analyzer:
  language:
    strict-casts: true
    strict-raw-types: true

This uses the standard lints package in pubspec.yaml:

dev_dependencies:
  lints: ^2.0.0

Method 1: Direct conversion

Doing it this way is very succinct and everything is built in with the dart:convert library. The disadvantage is that we don’t have as much type safety, and it is easy to make typos when writing the map key names.

JSON → object

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

final map = jsonDecode(rawJson);
final name = map['name'] as String;
final age = map['age'] as int;
final person = Person(name, age);

Decoded JSON doesn’t include the types. It’s dynamic. So that’s why you needed to tell Dart the type using the as keyword.

Object → JSON

We will use jsonEncode(), but it only accepts numbers, Booleans, strings, nulls, lists or maps with string keys. So we have to convert our object to a map first:

final person = Person('Mary', 30);
final map = {
  'name': person.name,
  'age'…