Dart: Hello World 003 之 颱風來了室內時間比較多 XDD

Classes and objects

OOP 拉!

靠書的寫法已經 GG 了 LOL….

not_initialized_non_nullable_instance_field

Non-nullable instance field ‘{0}’ must be initialized.

Has a type that’s potentially non-nullable Doesn’t have an initializer Isn’t marked as late

void main() {
  Person clark = Person();
  clark.name = 'Clark';
  clark.age = 20;
  print('Name: ${clark.name},  Age: ${clark.age}, Blood Type:${clark.bloodType}, nickName: ${clark.nickName}');
}
// Name: Clark,  Age: 20, Blood Type:AB, nickName: null

class Person {
  // late
  late String name;
  late int age;
  // initializer
  String bloodType = 'AB';
  // can be null
  String? nickName;
}

In Dart, no identifiers such as Private or Public

unless begin (_) ===> consider Private

In Dart, 不用刻意加 new

Person clark = New Person(); 是完全一樣的啦!

Using getters and setters

void main() {
  /// person2
  Person2 p = Person2();
  p.name = "Tim";
  p.bloodType = "AB";
  p.age = 32;
  print("Person2: ${p.name} ${p.bloodType} ${p.age}");
  // Person2: Tim AB 18
}

class Person2 {
  late String name, bloodType;
  late int _age;

  set age(int years) {
    if (years > 0 && years < 30 ) {
      _age = years;
    } else {
      // 18 forever :)
      _age = 18;
    }
  }

  int get age {
    return _age;
  }
}

Constructors

In Dart, you can have only one unnamed constructor

but you can have any number of named constructor.

void main() {
  /// constructor
  Person3 p3NameAndAge = Person3.withNameAndAge('tim3', 'AB');
  Person3 p3Empty = Person3();

  print('${p3NameAndAge.name} ${p3NameAndAge.bloodType}');
  print('${p3Empty.name} ${p3Empty.bloodType}');
  // tim3 AB
  // null null
}


class Person3 {
  String? name, bloodType;
  // unnamed constructor
  Person3();
  // named constructor
  Person3.withNameAndAge(this.name, this.bloodType);
  Person3.empty();
}

好 Flutter 書介紹 dart 部分沒了 XDDDD

可以準備 進入重工了 :)