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Dart中的对象都继承自 Object 类，单继承（extend关键字）。Dart与Java、kotlin不同的是其无public、private、protected修饰符，默认public ，通过在属性名、方法名前加 _下划线 来定义是否私有。

实现一个简单的类

class Student {//默认publicfinal String name;//默认publicfinal int age;Student(this.name, this.age);@overridebool operator ==(Object other) {return identical(this, other) ||other is Student &&runtimeType == other.runtimeType &&name == other.name &&age == other.age;}@overrideint get hashCode => name.hashCode ^ age.hashCode;
}

import 'package:gsy_flutter_demo/model/Student.dart';main() {var stu = Student("Jack", 18);stu.name;stu.age;
}

在属性名、方法名前加 _下划线 来定义私有属性。

class Person {String _name = "jack";int _age = 18;
}

 

定义私有属性和方法的类需要抽离放到一个单独的文件或者模块中。否则不会生效，例如写在同一个文件中，仍然可以访问私有属性。

class Person {String _name = "jack";int _age = 18;
}main() {var person = Person();person._name;person._age;
}

 类定义&使用

与Java、Kotlin一样，使用 class 关键字定义一个类。实例化可以使用new关键字创建，也可以省略。

class Student {final String name;final int age;Student(this.name, this.age);@overridebool operator ==(Object other) {return identical(this, other) ||other is Student &&runtimeType == other.runtimeType &&name == other.name &&age == other.age;}@overrideint get hashCode => name.hashCode ^ age.hashCode;
}var stu = Student("Jack", 18);var stu2 = Student("Mike", 20);

构造函数

构造函数有四种形式：类名构造函数、命名构造函数、常量构造函数、工厂构造函数。
定义一个类，默认会有一个 无参构造函数，如果有父类，还会调用父类的无参构造函数。

类名构造函数

 Student(this.name, this.age);

命名构造函数(类名.修饰符 定义的函数)

  Student.create(String name) : this(name, 20);

注意：命名构造函数不可继承。

常量构造函数

如果类创建的对象不会改变，就可以在编译期就创建这个常量实例，并定义一个常量构造函数，并且确保所有成员变量都是final的。

//常量构造函数  
const Student(this.name, this.age);

工厂构造函数

工厂构造函数，构造函数私有，使用 factory 关键字进行定义，根据不同情况创建不同的对象。

class Fruit {final double price;final int weight;final String name;Fruit._(this.price, this.weight, this.name);//宸ュ巶鏋勯€犲嚱鏁版病鏈夎闂潈闄?factory Fruit(String name) {if (name == 'apple') {return Fruit._(12, 5, name);} else if (name == 'pear') {return Fruit._(15, 5, name);}return Fruit._(100, 100, name);}

get/set修饰符

class Fruit {final double price;final int weight;final String name;Fruit._(this.price, this.weight, this.name);//宸ュ巶鏋勯€犲嚱鏁版病鏈夎闂潈闄?factory Fruit(String name) {if (name == 'apple') {return Fruit._(12, 5, name);} else if (name == 'pear') {return Fruit._(15, 5, name);}return Fruit._(100, 100, name);}int? get fruitWeight => weight;set price(double price) {this.price = price;}

对象操作符

类型强转 as

Fruit apple = Fruit("apple");
int weight = (apple as Fruit).fruitWeight ?? 0;

类型判断 is

  if (apple is Fruit) {print("apple");}

级联操作 ..

apple..price = 100.0..weight = 100..name = "Fruit";

class Fruit {final double price;late final int weight;late final String name;Fruit._(this.price, this.weight, this.name);factory Fruit(String name) {if (name == 'apple') {return Fruit._(12, 5, name);} else if (name == 'pear') {return Fruit._(15, 5, name);}return Fruit._(100, 100, name);}int? get fruitWeight => weight;set price(double price) {this.price = price;}
}main() {Fruit apple = Fruit("apple");int weight = (apple as Fruit).fruitWeight ?? 0;if (apple is Fruit) {print("apple");}apple..price = 100.0..weight = 100..name = "Fruit";

 

继承

子类使用 extends 关键字继承父类，子类会继承父类的属性和方法 (构造方法除外)，使用 super 关键字调用父类属性/方法，或者给父类构造方法传参。

class Animal {late String name;late int type;Animal(this.name, this.type);
}class Tiger extends Animal {int weight;Tiger(super.name, super.type, this.weight);
}

接口和抽象类

接口的作用：解决多继承的二义性问题。即指的是多继承中方法和属性名称的冲突，编译器无法确定使用哪个父类的方法和属性。在Dart中，无interface关键字，所有类都被隐式定义成一个接口，任何类都可以作为接口被实现。Dart解决多继承、实现的二义性问题：子类必须将父类中所有属性和方法全部重写。

接口简单Demo

class DemoA {int num;DemoA(this.num);void printDemo() => print("DemoA");
}class DemoB {int num;DemoB(this.num);void printDemo() => print("DemoB");
}class DemoC implements DemoA, DemoB {@overrideint num = 6;@overridevoid printDemo() {print("DemoC");}}

注意：Java中的限制：接口中只能定义抽象成员和方法，且强制子类必须实现。

抽象类简单Demo

Dart中的抽象类不能被实例化，但可以包含 抽象方法  和 非抽象方法。

abstract class DemoA {String demoName;DemoA(this.demoName);void doA();void showA();void printA() {print("DemoA");}
}abstract class DemoB {String demoBName = "DemoB";void doDemoB();void showDemoB();void printDemoB() {print("DemoB");}
}class RealDemo implements DemoA, DemoB {@overrideString demoBName = "RealDemo";@overrideString demoName = "RealDemo";@overridevoid doA() {}@overridevoid doDemoB() {}@overridevoid printA() {}@overridevoid printDemoB() {}@overridevoid showA() {}@overridevoid showDemoB() {}
}

class RealDemo extends DemoA implements DemoB {@overrideString demoBName = "demoBName";RealDemo(super.demoName);@overridevoid doA() {}@overridevoid doDemoB() {}@overridevoid printDemoB() {}@overridevoid showA() {}@overridevoid showDemoB() {}
}

Mixins

Dart中使用with关键字，将一个类的功能添加到另一个类中 (该类可以复用其中的方法和属性)，从而能实现多继承。mixin 关键字来定义一个混入类。

mixin Run {void run() => print("run");
}class Animal {}mixin Swim on Animal {void swim() => print("swim");
}class Tiger with Run {}class Fish extends Animal with Swim, Run {}main() {var fish = Fish();fish.swim();fish.run();var tiger = Tiger();tiger.run();
}

swim
run
run

注意： on子句 指定该mixin可以混入的类类型，只能混入到继承了Animal的类中。

枚举和密封类

Dart使用enum关键字定义枚举类型，枚举中的成员都有一个对应的索引值（这个值从0开始）。

枚举简单Demo

enum VALUE { VALUE_A, VALUE_B, VALUE_C }main() {for (var elemntValue in VALUE.values) {print(elemntValue);}
}

VALUE.VALUE_A
VALUE.VALUE_B
VALUE.VALUE_C

枚举支持 扩展方法

enum VALUE { VALUE_A, VALUE_B, VALUE_C }extension VALUE_OPERATE on VALUE {static VALUE getValueByIndex(int index) => VALUE.values[index];
}main() {var value = VALUE_OPERATE.getValueByIndex(1);print(value);
}

VALUE.VALUE_B

增强型枚举

enum Month {January(str: "January", num: 1),February(str: "February", num: 1),March(str: "March", num: 1),April(str: "April", num: 1),May(str: "May", num: 1),June(str: "June", num: 1),July(str: "July", num: 1),August(str: "August", num: 1),September(str: "September", num: 1),October(str: "October", num: 1),November(str: "November", num: 1),December(str: "December", num: 1);const Month({required this.str, required this.num});final String str;final int num;
}main() {print(Month.December.str);
}

 

December

 密封类

与Kotlin类似，使用 sealed 关键字进行修饰，用于限制类的结构层次结构。

sealed class Status {}class StatusA extends Status {}class StatusB extends Status {}class StatusC extends Status {}String getStatusStr(Status status) {return switch (status) {StatusA() => "StatusA",StatusB() => "StatusB",StatusC() => "StatusC"};
}