Flutter: Dart Basics & Setup

Flutter is Google's cross-platform UI toolkit for iOS, Android, Web, Desktop from a single Dart codebase. Dart is a strongly-typed, null-safe language with async/await. Flutter renders its own widgets via Skia/Impeller — no platform UI components.

Dart Language Essentials

// Variables & types
var name = 'Alice';           // type inferred
String greeting = 'Hello';
int count = 42;
double pi = 3.14;
bool isActive = true;

// Null safety — all types non-nullable by default
String? nullable = null;      // ? makes it nullable
String nonNull = nullable!;   // ! force unwrap (throws if null)
String safe = nullable ?? 'default';  // null coalescing
int? length = nullable?.length;       // null-aware access

// final and const
final name2 = 'Alice';        // runtime constant (set once)
const pi2 = 3.14159;          // compile-time constant

// Collections
var list = [1, 2, 3];
var map = {'name': 'Alice', 'age': 30};
var set = {1, 2, 3};

// String interpolation
var msg = 'Hello, $name! You are ${30 + 1} years old.';

// Functions
int add(int a, int b) => a + b;              // arrow function
void greet({required String name}) { }       // named parameter

// Async/await
Future<String> fetchData() async {
  await Future.delayed(Duration(seconds: 1));
  return 'data';
}

// Pattern matching (Dart 3)
var result = switch (status) {
  'active' => 'Active',
  'inactive' => 'Inactive',
  _ => 'Unknown',
};

Classes & Mixins

// Class
class Animal {
  final String name;
  int _age;                     // private (convention: _ prefix)

  Animal(this.name, this._age); // shorthand constructor

  int get age => _age;          // getter
  set age(int value) {          // setter
    if (value > 0) _age = value;
  }

  String describe() => '$name, age $_age';

  @override
  String toString() => describe();
}

// Named constructor
class Color {
  final int r, g, b;
  const Color(this.r, this.g, this.b);
  const Color.red() : this(255, 0, 0);    // named constructor
  const Color.fromHex(String hex) :
    r = int.parse(hex.substring(1, 3), radix: 16),
    g = int.parse(hex.substring(3, 5), radix: 16),
    b = int.parse(hex.substring(5, 7), radix: 16);
}

// Mixin
mixin Flyable {
  void fly() => print('Flying!');
}

class Bird extends Animal with Flyable {
  Bird(super.name, super.age);
}

// Record (Dart 3)
var point = (x: 3.0, y: 4.0);
print(point.x);  // 3.0

Flutter Setup & Project Structure

# Install Flutter
# https://flutter.dev/docs/get-started/install

flutter --version
flutter doctor           # check environment setup
flutter create my_app    # create new project
cd my_app
flutter run              # run on connected device/emulator
flutter run -d chrome    # run as web app
flutter build apk        # build Android APK
flutter build ipa        # build iOS (macOS required)
flutter build web        # build web app
flutter test             # run tests
flutter pub get          # install dependencies
flutter pub add http     # add package

Project structure:
  lib/
    main.dart            — entry point (runApp)
    app.dart             — MaterialApp / CupertinoApp
    features/            — feature-based organization
      auth/
        screens/
        widgets/
        providers/
    core/
      theme/
      services/
      models/
  test/                  — widget + unit tests
  assets/                — images, fonts, data files
  pubspec.yaml           — dependencies and assets config