Lære JSON Parsing Without Pain | REST Fundamentals in Flutter

When you work with APIs in Flutter, most responses you receive will be in JSON format. JSON, which stands for JavaScript Object Notation, is a lightweight data-interchange format that is easy for humans to read and write and easy for machines to parse and generate. Since Dart cannot use JSON data directly, you need to parse JSON responses into Dart objects that your app can use. This process is called JSON parsing, and it is a critical part of working with REST APIs in Flutter.

main.dart


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import 'dart:convert';

void main() {
  // Example JSON string from an API response
  String jsonString = '{"id": 1, "name": "Alice", "email": "alice@example.com"}';

  // Decode the JSON string into a Map
  Map<String, dynamic> userMap = jsonDecode(jsonString);

  // Map the JSON Map to a Dart model
  User user = User.fromJson(userMap);

  // Print the user details
  print('Id: [1m${user.id}[0m, Name: [1m${user.name}[0m, Email: [1m${user.email}[0m');
}

class User {
  final int id;
  final String name;
  final String email;

  User({
    required this.id,
    required this.name,
    required this.email,
  });

  // Factory constructor to create a User from JSON Map
  factory User.fromJson(Map<String, dynamic> json) {
    return User(
      id: json['id'],
      name: json['name'],
      email: json['email'],
    );
  }
}

Using model classes for parsed data provides several advantages:

Allow you to define the structure and expected types for your data;
Make your code more predictable and maintainable;
Provide type safety, which helps catch errors at compile time instead of at runtime;
Make your code easier to read and understand, since each class represents a specific entity or concept from your API.

When you use models, you gain confidence that your data matches your expectations and your app is less likely to crash due to unexpected data types.

Note

When parsing JSON, you may encounter missing or unexpected fields in the response. To handle these situations safely, always provide default values or use null-aware operators in your model constructors. This helps prevent runtime errors when the API data does not match your expectations.

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