Dart对象，一些特殊运算符

main(List args) {
var name = null;

name ??= “lilei”;

print(name);

var name2 = null;
var temp = name2 ?? “lilei”;
print(temp);
}

级联运算符

main(List args) {
var p = Person()
..name = “why”
..eat()
..running();
}

class Person {
String name = “”;

void eat() {
print(“eating”);
}

void running() {
print(“running”);
}
}

命名构造函数

main(List args) {
var p = Person.withNameAgeHeight(“sss”, 12, 1.78);
print(p.age);
}

class Person {
String name;
int age;
double height = 0;

Person(this.name, this.age);

Person.withNameAgeHeight(this.name, this.age, this.height);
}

类初始化列表

main(List args) {

}

class Person {
final String name;
final int age;

Person(this.name, {int age}) : this.age = age ?? 10 {}
}

构造函数的重定向

main(List args) {
var p = Person(“why”);
print(p.age);
}

class Person {
String name;
int age;

Person(String name) : this._internal(name, 0);

Person._internal(this.name, this.age);
}

常量构造函数

main(List args) {
const p1 = Person(“ss”);
const p12 = Person(“ss”);
print(identical(p1, p12));
}

class Person {
final String name;
const Person(this.name);
}

工厂构造函数

class People {
String name;
int age, sex;
static People _cache;

People() {
print(‘Dart —> People()’);
}

People.fromMap(map) {
this.name = map[‘name’];
this.age = map[‘age’];
this.sex = map[‘sex’];
print(‘Dart —> People.fromMap($map) —> $name, $age, $sex’);
}

factory People.map(map) {
if (People._cache == null) {
People._cache = new People.fromMap(map);
print(
‘Dart —> People.map($map) —> ${map[‘name’]}, ${map[‘age’]}, ${map[‘sex’]} —> People._cache == null’);
}
print(
‘Dart —> People.map($map) —> ${map[‘name’]}, ${map[‘age’]}, ${map[‘sex’]}’);
return People._cache;
}

factory People.fromJson(json) => People();
}