xdart-test/lib/Spacecraft.dart

import 'package:dio/dio.dart';

//https://dart.cn/codelabs/dart-cheatsheet

class Spacecraft {
  String name;
  DateTime launchDate;

  final _lock = Lock();

  int _aProperty = 0;

  var _values = <int>[];

  void addCount(int num) {
    _lock.lock();
    _values.add(num);
    _lock.unlock();
  }

  //get values len
  int get len => _values.length;

  int get aProperty => _aProperty;

  set aProperty(int value) {
    _aProperty = value;
  }

  // 构造函数，带有可以直接为成员变量赋值的语法糖。
  Spacecraft(this.name, this.launchDate) {
    // 这里可以实现初始化代码。
  }

  // 命名构造函数，转发到默认构造函数。
  Spacecraft.unlaunched(String name) : this(name, null);

  // 只读的非 final 的属性
  // ？ ； isnull
  //launchDate!=null
//  int get launchYear => launchDate != null ? launchDate.year : 0;
  int get launchYear => launchDate?.year;

  // 方法。
  void describe() {
    _lock.lock();
    try {
      print('宇宙飞船：$name');
      if (launchDate != null) {
        // ignore: omit_local_variable_types
        int years = DateTime.now().difference(launchDate).inDays ~/ 365;
        print('发射时间：$launchYear ($years years ago)');
      } else {
        print('尚未发射');
      }
    } finally {
      _lock.unlock();
    }
  }
}

class Orbiter extends Spacecraft {
  //属性
  num altitude;

  Orbiter.Check(this.altitude) : super(null, null);

  Orbiter(String name, DateTime launchDate, this.altitude)
      : super(name, launchDate);

  //
  @override
  String toString() {
    return 'Orbiter{altitude: $altitude}';
  }
}

//sudo "/Applications/Install macOS Catalina.app/Contents/Resources/createinstallmedia" --volume /Volumes/CantChat
class Shape {
  Shape();

  //factory constructors
  //can return sub class object
  factory Shape.fromTypeName(String typeName) {
    if (typeName == 'square') return Square();
    if (typeName == 'circle') return Circle();
    print('I don\'t recognize $typeName');
    return null;
  }
}

class Square extends Shape {}

class Circle extends Shape {}