Class và Object

🎯 Mục tiêu: OOP cơ bản với class trong Dart.

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💡 Định nghĩa Class

class Person {
  String name;
  int age;

  Person(this.name, this.age);

  void greet() {
    print("Hello, I'm $name");
  }
}

void main() {
  var person = Person("Alice", 25);
  person.greet();
}

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📝 Properties

class User {
  final String id;
  String name;
  int _age = 0;  // Private (underscore)

  User(this.id, this.name);

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

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🔧 Initializer List

class Point {
  final double x;
  final double y;
  final double distance;

  Point(double x, double y)
      : x = x,
        y = y,
        distance = sqrt(x * x + y * y);
}

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📱 Trong Flutter

class UserModel {
  final String id;
  final String name;
  final String? avatar;

  const UserModel({
    required this.id,
    required this.name,
    this.avatar,
  });
}

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✅ Checklist

• Dùng this. trong constructor
• _ prefix cho private
• Getters và setters

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