Networking and APIs

dependencies:
  http: ^1.1.0
  dio: ^5.4.0        # Alternative with interceptors

import 'dart:convert';
import 'package:http/http.dart' as http;

class ApiService {
  static const String baseUrl = 'https://api.example.com';

  // GET request
  static Future<List<User>> getUsers() async {
    final response = await http.get(
      Uri.parse('$baseUrl/users'),
      headers: {'Authorization': 'Bearer $token'},
    );

    if (response.statusCode == 200) {
      final List data = jsonDecode(response.body);
      return data.map((json) => User.fromJson(json)).toList();
    } else {
      throw ApiException('Failed to load users: ${response.statusCode}');
    }
  }

  // POST request
  static Future<User> createUser(Map<String, dynamic> data) async {
    final response = await http.post(
      Uri.parse('$baseUrl/users'),
      headers: {
        'Content-Type': 'application/json',
        'Authorization': 'Bearer $token',
      },
      body: jsonEncode(data),
    );

    if (response.statusCode == 201) {
      return User.fromJson(jsonDecode(response.body));
    } else {
      throw ApiException('Failed to create user');
    }
  }

  // PUT request
  static Future<User> updateUser(String id, Map<String, dynamic> data) async {
    final response = await http.put(
      Uri.parse('$baseUrl/users/$id'),
      headers: {
        'Content-Type': 'application/json',
        'Authorization': 'Bearer $token',
      },
      body: jsonEncode(data),
    );

    if (response.statusCode == 200) {
      return User.fromJson(jsonDecode(response.body));
    } else {
      throw ApiException('Failed to update user');
    }
  }

  // DELETE request
  static Future<void> deleteUser(String id) async {
    final response = await http.delete(
      Uri.parse('$baseUrl/users/$id'),
      headers: {'Authorization': 'Bearer $token'},
    );

    if (response.statusCode != 204) {
      throw ApiException('Failed to delete user');
    }
  }
}

class ApiException implements Exception {
  final String message;
  ApiException(this.message);
  
  @override
  String toString() => 'ApiException: $message';
}

class User {
  final String id;
  final String name;
  final String email;
  final DateTime createdAt;

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

  // JSON → Object
  factory User.fromJson(Map<String, dynamic> json) {
    return User(
      id: json['id'],
      name: json['name'],
      email: json['email'],
      createdAt: DateTime.parse(json['created_at']),
    );
  }

  // Object → JSON
  Map<String, dynamic> toJson() {
    return {
      'name': name,
      'email': email,
    };
  }

  // Copy with modifications
  User copyWith({String? name, String? email}) {
    return User(
      id: id,
      name: name ?? this.name,
      email: email ?? this.email,
      createdAt: createdAt,
    );
  }
}

class UsersPage extends StatefulWidget {
  const UsersPage({super.key});

  @override
  State<UsersPage> createState() => _UsersPageState();
}

class _UsersPageState extends State<UsersPage> {
  List<User> _users = [];
  bool _loading = true;
  String? _error;

  @override
  void initState() {
    super.initState();
    _loadUsers();
  }

  Future<void> _loadUsers() async {
    setState(() {
      _loading = true;
      _error = null;
    });

    try {
      final users = await ApiService.getUsers();
      setState(() {
        _users = users;
        _loading = false;
      });
    } catch (e) {
      setState(() {
        _error = e.toString();
        _loading = false;
      });
    }
  }

  @override
  Widget build(BuildContext context) {
    if (_loading) return const Center(child: CircularProgressIndicator());
    if (_error != null) {
      return Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            Text('Error: $_error'),
            ElevatedButton(onPressed: _loadUsers, child: Text('Retry')),
          ],
        ),
      );
    }

    return RefreshIndicator(
      onRefresh: _loadUsers,
      child: ListView.builder(
        itemCount: _users.length,
        itemBuilder: (context, index) {
          final user = _users[index];
          return ListTile(
            leading: CircleAvatar(child: Text(user.name[0])),
            title: Text(user.name),
            subtitle: Text(user.email),
          );
        },
      ),
    );
  }
}

import 'package:dio/dio.dart';

final dio = Dio(BaseOptions(
  baseUrl: 'https://api.example.com',
  connectTimeout: Duration(seconds: 5),
  receiveTimeout: Duration(seconds: 3),
  headers: {'Authorization': 'Bearer $token'},
));

// Interceptor for logging
dio.interceptors.add(LogInterceptor(requestBody: true, responseBody: true));

// Error handling interceptor
dio.interceptors.add(InterceptorsWrapper(
  onError: (error, handler) async {
    if (error.response?.statusCode == 401) {
      // Refresh token
      final newToken = await refreshAuthToken();
      error.requestOptions.headers['Authorization'] = 'Bearer $newToken';
      // Retry the request
      final response = await dio.fetch(error.requestOptions);
      return handler.resolve(response);
    }
    handler.next(error);
  },
));

// Usage
final response = await dio.get('/users');