Dart学习3

柳ll
104 阅读2分钟

类

定义、使用类

定义

class Point {
}

使用

var p = Point();

构造函数

定义

class Point {
  num x, y;

  Point(this.x, this.y);

  @override
  String toString() {
    return "$x, $y";
  }
}

使用

var p = Point(1, 2);
print(p);

1, 2

初始化列表

定义

class Point {
  num x, y;
  Map origin1, origin2;

  Point(this.x, this.y)
      : origin1 = {'x': x, 'y': y},
        origin2 = {'x': x + 10, 'y': y + 10};
}

使用

void main(List<String> args) {
  var p = Point(1, 2);
  print(p);

1, 2, {1: 1, 2: 2}, {1: 2, 2: 4}

命名构造函数

定义

class Point {
  num x, y;
  Map origin1, origin2;

  Point.fromJson(Map json)
      : x = json['x'],
        y = json['y'],
        origin1 = {'x': json['x'], 'y': json['y']},
        origin2 = {'x': json['x'] + 10, 'y': json['y'] + 10};
}

使用

var p = Point.fromJson({"x": 1, "y": 2});
print(p);

10, 20, {x: 10, y: 20}, {x: 20, y: 30}

重定向构造函数

定义

class Point {
  num x, y;
  Map origin1, origin2;

  Point(this.x, this.y)
      : origin1 = {'x': x, 'y': y},
        origin2 = {'x': x + 10, 'y': y + 10};

  // 重定向构造函数
  Point.fromJson(Map json) : this(json['x'], json['y']);
}

使用

var p = Point.fromJson({"x": 1, "y": 2});
print(p);

10, 20, {x: 10, y: 20}, {x: 20, y: 30}

callable

class IOSPhone {
  call(String num) {
    print('phone number is $num');
  }
}

main(List<String> args) {
  var phone = IOSPhone();
  phone('911');
}

phone number is 911

get set

定义、使用 get set

定义

class People {
  String? _name;

  People();

  set name(String value) {
    _name = value;
  }

  String get name {
    return 'people is $_name';
  }
}

使用

var p = People();
p.name = 'ducafecat';
print(p.name);

people is ducafecat

简化 get set

class People {
  String? _name;

  People();

  set name(String value) => _name = value;

  String get name => 'people is $_name';
}

业务场景

购物车

  /// 商品数量
  int get lineItemsCount => lineItems.length;

  /// 运费
  double get shipping => 0;

  /// 折扣
  double get discount =>
      lineCoupons.fold<double>(0, (double previousValue, CouponsModel element) {
        return previousValue + (double.parse(element.amount ?? "0"));
      });

  /// 商品合计价格
  double get totalItemsPrice =>
      lineItems.fold<double>(0, (double previousValue, LineItem element) {
        return previousValue + double.parse(element.total ?? "0");
      });

以前可能会写个方法 getXXX() 当然也适用于赋值操作

static

静态变量

static 定义

声明

class People {
  static String name = 'ducafecat';
}

调用

静态变量可以通过外部直接访问,不需要将类实例化

print(People.name);

ducafecat

函数内部访问

实例化后的类也可以访问该静态变量

声明

class People {
  static String name = 'ducafecat';
  void show() {
    print(name);
  }
}

调用

People().show();

ducafecat

静态方法

静态方法可以通过外部直接访问

声明

class People {
  static String name = 'ducafecat';
  static void printName() {
    print(name);
  }
}

调用

People.printName();

ducafecat

业务场景

EasyLoading 用大量的 static 来方便方法调用

抽象

abstract 类、函数、成员

  • 普通类前加 abstract
abstract class Person {
  String name = 'ducafecat';
  void printName() {
    print(name);
  }
}

不能直接 new 实例化

var p = Person();
p.printName();

Abstract classes can't be instantiated.
Try creating an instance of a concrete subtype.

继承方式使用

class Teacher extends Person {
}

var p = Teacher();
p.printName();

ducafecat

接口方式使用

定义

abstract class Person {
  String name = '';
  void printName();
}

class Teacher implements Person {
  @override
  String name;

  Teacher(this.name);

  @override
  void printName() {
    print('Teacher: $name');
  }
}

实例

var p = Teacher("ducafecat");
p.printName();

ducafecat

接口

  • Dart 没有接口

dart.dev/samples#int…

接口方式使用

  • 定义人抽象类
abstract class IPerson {
  String name;
  int age;

  IPerson(this.name, this.age);

  String info() {
    return 'Name: $name, Age: $age';
  }
}

接口用途的抽象类 请用字母 I 开头 , 如 IPhone

  • 老师
class Teacher implements IPerson {
  @override
  String name;

  @override
  int age;

  Teacher(this.name, this.age);

  @override
  String info() {
    return 'Teacher -> Name: $name, Age: $age';
  }
}
  • 学生
class Student implements IPerson {
  @override
  int age;

  @override
  String name;

  Student(this.name, this.age);

  @override
  String info() {
    return 'Student -> Name: $name, Age: $age';
  }
}
  • 打印信息
void makePersonInfo(IPerson user) => print(user.info());
  • 实例化
void main(List<String> args) {
  var t = Teacher('ducafecat', 99);
  makePersonInfo(t);

  var s = Student('hans', 66);
  makePersonInfo(s);
}

Teacher -> Name: ducafecat, Age: 99
Student -> Name: hans, Age: 66

履行多接口

  • 定义学校抽象类
abstract class ISchool {
  int grade;

  ISchool(this.grade);

  String schoolInfo() {
    return 'Grade: $grade';
  }
}
  • 学生 多继承
class Student implements IPerson, ISchool {
  @override
  int age;

  @override
  String name;

  @override
  int grade;

  Student(this.name, this.age, this.grade);

  @override
  String info() {
    return 'Student -> Name: $name, Age: $age';
  }

  @override
  String schoolInfo() {
    return 'School -> Name: $name, Age: $age, Grade: $grade';
  }
}
  • 打印信息
void makePersonInfo(IPerson user) => print(user.info());
void makeSchoolInfo(ISchool user) => print(user.schoolInfo());
  • 实例化
void main(List<String> args) {
  var t = Teacher('ducafecat', 99);
  makePersonInfo(t);

  var s = Student('hans', 66, 5);
  makePersonInfo(s);
  makeSchoolInfo(s);
}

Teacher -> Name: ducafecat, Age: 99
Student -> Name: hans, Age: 66
School -> Name: hans, Age: 66, Grade: 5

从一个普通类履行接口

class Phone {
  void startup() {
    print('开机');
  }

  void shutdown() {
    print('关机');
  }
}

class AndroidPhone implements Phone {
  @override
  void startup() {
    print('AndroidPhone 开机');
  }

  @override
  void shutdown() {
    print('AndroidPhone 关机');
  }
}

void main() {
  var p = AndroidPhone();
  p.startup();
  p.shutdown();
}

Dart 可以从一个普通的类履行接口

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