Lære JSON Serialization in Dart for Flutter | Writing Clean Dart for Scalable Flutter Apps

JSON serialization is the process of converting Dart objects into JSON format and vice versa. This is essential in Flutter apps because most APIs and network services communicate using JSON. By serializing and deserializing data, you can easily send and receive structured information between your app and backend services. Clean and reliable JSON handling is critical for scalable, maintainable Flutter code.

Note

Always check for the presence and type of fields in your JSON data to avoid runtime errors. Defensive parsing ensures your Flutter app remains robust even when backend data changes or is incomplete.

main.dart


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class User {
  final String name;
  final int age;

  User({required this.name, required this.age});

  // Deserialize from JSON
  factory User.fromJson(Map<String, dynamic> json) {
    return User(
      name: json['name'] as String,
      age: json['age'] as int,
    );
  }

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

void main() {
  // Example: Serialize
  User user = User(name: 'Alice', age: 30);
  Map<String, dynamic> json = user.toJson();
  print(json);

  // Example: Deserialize
  User anotherUser = User.fromJson({'name': 'Bob', 'age': 25});
  print('${anotherUser.name}, ${anotherUser.age}');
}

When working with JSON from network sources, you may encounter null or missing fields. Dart's null safety helps, but you should always handle these cases explicitly. Use default values or null-aware operators to avoid runtime errors when fields are absent or have unexpected types.

main.dart


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import 'package:flutter/material.dart';

class Product {
  final String title;
  final double price;

  Product({required this.title, required this.price});

  factory Product.fromJson(Map<String, dynamic> json) {
    return Product(
      title: json['title'] as String? ?? 'Unknown',
      price: (json['price'] is num) ? (json['price'] as num).toDouble() : 0.0,
    );
  }
}

class ProductWidget extends StatelessWidget {
  final Map<String, dynamic> jsonData;

  const ProductWidget({super.key, required this.jsonData});

  @override
  Widget build(BuildContext context) {
    final product = Product.fromJson(jsonData);
    return ListTile(
      title: Text(product.title),
      subtitle: Text('Price: \$${product.price}'),
    );
  }
}

void main() {
  runApp(MaterialApp(
    home: Scaffold(
      body: ProductWidget(jsonData: {'title': null, 'price': 'not a number'}),
    ),
  ));
}

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main.dart


              123456789101112131415161718192021222324252627282930313233
            
class User {
  final String name;
  final int age;

  User({required this.name, required this.age});

  // Deserialize from JSON
  factory User.fromJson(Map<String, dynamic> json) {
    return User(
      name: json['name'] as String,
      age: json['age'] as int,
    );
  }

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

void main() {
  // Example: Serialize
  User user = User(name: 'Alice', age: 30);
  Map<String, dynamic> json = user.toJson();
  print(json);

  // Example: Deserialize
  User anotherUser = User.fromJson({'name': 'Bob', 'age': 25});
  print('${anotherUser.name}, ${anotherUser.age}');
}

main.dart


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import 'package:flutter/material.dart';

class Product {
  final String title;
  final double price;

  Product({required this.title, required this.price});

  factory Product.fromJson(Map<String, dynamic> json) {
    return Product(
      title: json['title'] as String? ?? 'Unknown',
      price: (json['price'] is num) ? (json['price'] as num).toDouble() : 0.0,
    );
  }
}

class ProductWidget extends StatelessWidget {
  final Map<String, dynamic> jsonData;

  const ProductWidget({super.key, required this.jsonData});

  @override
  Widget build(BuildContext context) {
    final product = Product.fromJson(jsonData);
    return ListTile(
      title: Text(product.title),
      subtitle: Text('Price: \$${product.price}'),
    );
  }
}

void main() {
  runApp(MaterialApp(
    home: Scaffold(
      body: ProductWidget(jsonData: {'title': null, 'price': 'not a number'}),
    ),
  ));
}

Alt var klart?

Takk for tilbakemeldingene dine!

Seksjon 3. Kapittel 2