函数入参的默认值

// 示例
class Person {
  String? language;
  String? nation;
  String? name;
  int? age;

  Person(this.name, this.age);
  
  // 带有默认参数的入参需要被放在参数列表的最后，并且用 {} 包裹起来，表示为可选参数
  Person.Chinese(String name, int age, {String nation = "Chinese", String language = "Mandarin"}) {
    this.name = "name";
    this.age = 0;
  }
}

---

构造函数

有三种构造函数，默认构造函数、命名构造函数、带有初始化列表的构造函数

class Person {
  String? language;
  String? nation;
  String? name;
  int? age;

  // 1. 默认构造函数
  Person(this.name, this.age);

  // 2. 命名构造函数
  Person.Chinese(String name, int age, {String nation = "Chinese", String language = "Mandarin"}) {
    this.name = "name";
    this.age = 0;
  }

  // 3. 构造函数 + 初始化列表
  Person.USA(String name, int age, {String nation = "English", String language = "English"}) : this.name = name, this.age = age, language = "", nation = "" {
    this.name = "United States Of America";
  }
}

带有初始化列表的构造函数被：隔开分两部分。：的后半部分是初始化列表部分，用来初始化成员变量，且初始化列表执行时机早于初始化函数的函数体。

void main() {
  Person usa = Person.USA("USA", 18);
  print("${usa.name}"); // 输出： United States Of America
}

---

异步回调

两种方式：1. 通过 <async await> 构造异步回调 2. 通过 <回调函数> 构造异步回调

void main() {
  asyncfoo();  
  print("========");
  blockfoo();
}


asyncfoo() {
  print("== start ==");
  var result = _asyncfoo();
  print(result);
  print("== end ==");
}

// 通过 <async await> 构造异步回调
Future _asyncfoo()  async {
  await Future.delayed(const Duration(seconds: 2));
  return Future.value("Result String ->> _asyncfoo");
}



void blockfoo() {
  print("== start ==");
  _blockfoo((value) {
    print(value);
  });
  print("== end ==");
}

// 通过 <回调函数> 构造异步回调
Future<void> _blockfoo(Function(String) callback) async {
  await Future.delayed(const Duration(seconds: 2));
  callback("Result String ->> _blockfoo");
}

---

enum
enum GMBottomNavigationBarModule {
discovery,
vehicle,
profile,
discoveryScrollback; //this enum will be display, it's other state of

static GMBottomNavigationBarModule module(int index) =>
GMBottomNavigationBarModule.values
.firstWhere((element) => element.index == index);

bool get isDiscovery {
switch (this) {
case GMBottomNavigationBarModule.discovery:
case GMBottomNavigationBarModule.discoveryScrollback:
return true;
case GMBottomNavigationBarModule.vehicle:
case GMBottomNavigationBarModule.profile:
return false;
}
}

---

List

sort

高阶函数map/reduce/where，where 类比于 swift 的 filter

class Person {
  int age;
  Person(this.age);

  String toString() {
    return "age is ${this.age}";
  }
}

void main() {
  List<Person> persons = [
    Person(10),
    Person(20),
    Person(30),
  ];

  // Map
  var newLists = persons.map((e) => e.age + 1);
  print(newLists); // output: 11, 21, 31

  // Reduce
  var ageSum = persons.map((e) => e.age).reduce((a,b) => a + b);
  print(ageSum); // output: 60

  // Where 类似 swift 的 filter
  var overTenList = persons.where((a) => a.age > 10).toList();
  print(overTenList); // output:  [age is 20,  age is 30]
}