dart-expert

Dart & Flutter Expert

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Install skill "dart-expert" with this command: npx skills add personamanagmentlayer/pcl/personamanagmentlayer-pcl-dart-expert

Dart & Flutter Expert

Expert guidance for Dart programming, Flutter framework, mobile development, and cross-platform applications.

Core Concepts

Dart Language

  • Strong typing with type inference

  • Async/await and Futures

  • Streams

  • Mixins and extensions

  • Null safety

  • Collections

Flutter Framework

  • Widgets (Stateless & Stateful)

  • State management (Provider, Riverpod, Bloc)

  • Navigation and routing

  • Material and Cupertino design

  • Responsive layouts

  • Platform integration

Dart Fundamentals

// Variables and types var name = 'John'; // Type inference String explicitType = 'Explicit'; final constantValue = 42; // Runtime constant const compileConstant = 'Compile-time';

// Null safety String? nullableString; String nonNullable = 'Never null';

// Late initialization late String lateInit;

// Collections List<String> names = ['Alice', 'Bob', 'Charlie']; Map<String, int> ages = {'Alice': 25, 'Bob': 30}; Set<int> uniqueNumbers = {1, 2, 3, 3}; // {1, 2, 3}

// Functions int add(int a, int b) => a + b;

// Named parameters void createUser({ required String name, int age = 18, String? email, }) { print('Creating user: $name, age: $age'); }

// Classes class User { final String id; final String name; int age;

User({ required this.id, required this.name, this.age = 0, });

// Named constructor User.guest() : this(id: 'guest', name: 'Guest');

// Methods void celebrateBirthday() { age++; }

@override String toString() => 'User($name, $age)'; }

// Mixins mixin Loggable { void log(String message) { print('[${DateTime.now()}] $message'); } }

class LoggableUser extends User with Loggable { LoggableUser({required String id, required String name}) : super(id: id, name: name); }

// Extensions extension StringExtensions on String { bool get isValidEmail => contains('@') && contains('.'); String capitalize() => '${this[0].toUpperCase()}${substring(1)}'; }

Async Programming

import 'dart:async';

// Future Future<String> fetchUser(String id) async { await Future.delayed(Duration(seconds: 1)); return 'User $id'; }

// Error handling Future<User?> fetchUserSafely(String id) async { try { final user = await fetchUser(id); return User(id: id, name: user); } catch (e) { print('Error: $e'); return null; } }

// Multiple futures Future<void> fetchMultiple() async { final results = await Future.wait([ fetchUser('1'), fetchUser('2'), fetchUser('3'), ]); print(results); }

// Streams Stream<int> countStream() async* { for (int i = 1; i <= 5; i++) { await Future.delayed(Duration(seconds: 1)); yield i; } }

// Listen to stream void listenToStream() { countStream().listen( (data) => print('Received: $data'), onError: (error) => print('Error: $error'), onDone: () => print('Done'), ); }

// Stream transformations Stream<String> transformedStream() { return countStream() .where((n) => n % 2 == 0) .map((n) => 'Number: $n') .take(3); }

// StreamController class Counter { final _controller = StreamController<int>();

Stream<int> get stream => _controller.stream;

void increment(int value) { _controller.add(value); }

void dispose() { _controller.close(); } }

Flutter Widgets

import 'package:flutter/material.dart';

// Stateless Widget class UserCard extends StatelessWidget { final User user;

const UserCard({Key? key, required this.user}) : super(key: key);

@override Widget build(BuildContext context) { return Card( child: ListTile( title: Text(user.name), subtitle: Text('Age: ${user.age}'), trailing: Icon(Icons.arrow_forward), ), ); } }

// Stateful Widget class CounterWidget extends StatefulWidget { const CounterWidget({Key? key}) : super(key: key);

@override State<CounterWidget> createState() => _CounterWidgetState(); }

class _CounterWidgetState extends State<CounterWidget> { int _counter = 0;

void _incrementCounter() { setState(() { _counter++; }); }

@override Widget build(BuildContext context) { return Column( children: [ Text('Counter: $_counter'), ElevatedButton( onPressed: _incrementCounter, child: Text('Increment'), ), ], ); } }

// Layout class UserListScreen extends StatelessWidget { final List<User> users;

const UserListScreen({Key? key, required this.users}) : super(key: key);

@override Widget build(BuildContext context) { return Scaffold( appBar: AppBar( title: Text('Users'), actions: [ IconButton( icon: Icon(Icons.add), onPressed: () => Navigator.push( context, MaterialPageRoute(builder: (_) => AddUserScreen()), ), ), ], ), body: ListView.builder( itemCount: users.length, itemBuilder: (context, index) { return UserCard(user: users[index]); }, ), ); } }

State Management (Provider)

import 'package:provider/provider.dart';

// State class class UserProvider extends ChangeNotifier { List<User> _users = [];

List<User> get users => _users;

Future<void> fetchUsers() async { _users = await api.getUsers(); notifyListeners(); }

void addUser(User user) { _users.add(user); notifyListeners(); }

void removeUser(String id) { _users.removeWhere((user) => user.id == id); notifyListeners(); } }

// Setup provider void main() { runApp( MultiProvider( providers: [ ChangeNotifierProvider(create: () => UserProvider()), ChangeNotifierProvider(create: () => AuthProvider()), ], child: MyApp(), ), ); }

// Consume provider class UserList extends StatelessWidget { @override Widget build(BuildContext context) { final userProvider = Provider.of<UserProvider>(context);

return ListView.builder(
  itemCount: userProvider.users.length,
  itemBuilder: (context, index) {
    final user = userProvider.users[index];
    return ListTile(
      title: Text(user.name),
      trailing: IconButton(
        icon: Icon(Icons.delete),
        onPressed: () => userProvider.removeUser(user.id),
      ),
    );
  },
);

} }

// Consumer widget class UserCounter extends StatelessWidget { @override Widget build(BuildContext context) { return Consumer<UserProvider>( builder: (context, userProvider, child) { return Text('Total users: ${userProvider.users.length}'); }, ); } }

Navigation

// Basic navigation Navigator.push( context, MaterialPageRoute(builder: (context) => DetailScreen()), );

// Named routes MaterialApp( routes: { '/': (context) => HomeScreen(), '/details': (context) => DetailScreen(), '/settings': (context) => SettingsScreen(), }, );

Navigator.pushNamed(context, '/details');

// Pass arguments Navigator.pushNamed( context, '/details', arguments: {'userId': '123'}, );

// Get arguments final args = ModalRoute.of(context)!.settings.arguments as Map;

// Return data final result = await Navigator.push( context, MaterialPageRoute(builder: (_) => SelectionScreen()), );

// Pop with result Navigator.pop(context, selectedValue);

HTTP and API

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

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

Future<List<User>> fetchUsers() async { final response = await http.get(Uri.parse('$baseUrl/users'));

if (response.statusCode == 200) {
  final List&#x3C;dynamic> data = json.decode(response.body);
  return data.map((json) => User.fromJson(json)).toList();
} else {
  throw Exception('Failed to load users');
}

}

Future<User> createUser(User user) async { final response = await http.post( Uri.parse('$baseUrl/users'), headers: {'Content-Type': 'application/json'}, body: json.encode(user.toJson()), );

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

} }

// Model with JSON serialization class User { final String id; final String name; final String email;

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

factory User.fromJson(Map<String, dynamic> json) { return User( id: json['id'], name: json['name'], email: json['email'], ); }

Map<String, dynamic> toJson() { return { 'id': id, 'name': name, 'email': email, }; } }

Best Practices

Dart

  • Use const constructors when possible

  • Leverage null safety

  • Use final for immutable values

  • Prefer async/await over .then()

  • Use extensions for utility methods

  • Follow Effective Dart guidelines

Flutter

  • Keep widgets small and focused

  • Use const widgets for optimization

  • Avoid rebuilding entire trees

  • Implement proper state management

  • Handle errors gracefully

  • Test widgets thoroughly

  • Use keys when needed

Performance

  • Use ListView.builder for long lists

  • Implement pagination

  • Cache network images

  • Minimize widget rebuilds

  • Use const constructors

  • Profile app performance

  • Lazy load resources

Anti-Patterns

❌ Large widget trees ❌ State in StatelessWidget ❌ Not disposing controllers ❌ Ignoring null safety ❌ Synchronous I/O in UI ❌ No error handling ❌ Hard-coded strings

Resources

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