Summary - JSON

Combine jsonDecode, fromJson and json_serializable to write an API client.

Summary - JSON

This group covered JSON serialization in Dart: jsonDecode (String → dynamic), jsonEncode (object → String), fromJson (Map → class), toJson (class → Map), json_serializable (auto generation).

Core: jsonEncode does not accept a class directly; toJson is needed first. fromJson gives type-safe access. json_serializable auto-generates this code.

Symmetric design: fromJson(toJson(u)) == u. This gives a lossless serialization round-trip.

Exercise Summary: decode + fromJson

Add import 'dart:convert';. Define class User { String name; User(this.name); factory User.fromJson(Map<String, dynamic> m) => User(m['name'] as String); }. Inside main add var u = User.fromJson(jsonDecode('{"name":"Ayşe"}') as Map<String, dynamic>); and print(u.name);.

Show example solution

import 'dart:convert';

class User {
  String name;
  User(this.name);
  factory User.fromJson(Map<String, dynamic> m) => User(m['name'] as String);
}

void main() {
  var u = User.fromJson(jsonDecode('{"name":"Ayşe"}') as Map<String, dynamic>);
  print(u.name);
}

Test yourself

What does jsonEncode(u) do (u is a class)?
- Returns a Map
- Throws an error
- Calls toJson automatically
- Empty String
Show answer

Throws an error — jsonEncode does not accept a class directly; it throws.
Match the concepts

jsonDecode

String → dynamic
jsonEncode

Object → String
fromJson

Map → class
toJson

Class → Map

Type cast

m['name'] ____ String

Show answer

m['name'] as String

Next lesson: sqflite

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