---
title: fireship dart full course
tags: dart,flutter,fireship
description: fireship dart full course
---

#### 运行时类型

- `(num1 + num2) is int` 返回boolean
- `runtimeType` 属性返回运行时类型


---

#### NULL SAFETY
> variables cannot be null
> 除非你声明它们可空，它们的值都不能为空
##### 所以以下代码没问题

void main() {
  int? age = null;
  print(age);
  Animal animal = Animal();
  animal.sayName();
}

---

##### late 关键词
> assign a non-nullable value later

void main() {
  Animal animal = Animal();
  animal.sayName();
}



class Animal{
  late final String? name;
  void sayName(){
    name = 'xiaosong';
    print(name);
  }
}

---

#### 随机整数

import "dart:math";
  
void main(){
    for(var i=0;i<=10;i++){
      print(i);
    var r = new Random();
    int rn = r.nextInt(100);
    if(rn>50){
      print(rn);
      break;
    }else{
      print(rn);
      continue;
    }
  }
}

> 重点

import "dart:math";
var r = new Random();
int rn = r.nextInt(100);

---

#### assert 断言
- 调试的时候很有用,生产环境不运行
- assert函数第一个参数是一个返回boolean的表达式
- 第二个参数是一个可选文本参数，如断言失败会print出来

void main(){
  int age = 32;
  int res = 100;
  assert(age==res,'age should be $res');
  print('good');
}

___

#### 一些操作符

##### ??=
> assign value if null,otherwise use current value

import "dart:math";
  
void main(){
  String? name;
  name = 'xiaosong';
  name ??='zhang';
  print('name is $name');
}

---

##### ??

import "dart:math";
  
void main(){
  String? name;
  var res = name ?? 'elive';
  print('result is $res');
}

---

##### 三元操作符 boolean ? a : b

String color = 'blue';
var isThisBlue = color == 'blue' ? 'Yep, blue it is' : 'Nah, it aint blue';

---

#### cascade
> call method,but return original object;

- old

  
void main(){
 
  Robot cleanRobot = Robot();
  cleanRobot.name = 'clean';
  cleanRobot.age = 5;
  print('robot name is ${cleanRobot.name}');
}


class Robot {
  late final String name;
  late final int age;
  
}

- with cascade

void main(){
 
  Robot cleanRobot = Robot()
  ..name = 'clean new'
  ..age = 4;
  print('robot name is ${cleanRobot.name}');
}


class Robot {
  late final String name;
  late final int age;
}
  

---

#### typecast

void main(){
  var phoneNumber = 23 as double;
  print(phoneNumber is double);
  print(phoneNumber);
}

---

#### function 定义
> 以下写法合法

void main(){
  shout();
}

shout(){
  print('shout!!');
}

---

#### function 返回值

void main(){
  print(shout());
}

String shout(){
  print('shout!!');
  return 'shout string!';
}

---

#### function parameter

void main(){
  print(shout('dylan'));
}

String shout(String name){
  return 'good morning $name';
}

---

#### function default parameter
- 定义的时候需要在对象里面
- 可以不传参
- 如果传，则不需要在对象里面

void main(){
  print(shout());
  print(shout(name:'xiaosong'));
}

String shout({String name = 'world'}){
  return 'good morning $name';
}

void main(){
  shout('xiaosong', address:'wilmot',age:3);
}

shout(String name,{int age=32,String address='196a st'}){
  print(name);
  print(age);
  print(address);
}

---

#### function 多个参数
> 可以按顺序传

void main(){
  print(shout('xiaosong',42));
}

shout(String name, int age){
  print(name);
  print(age);
}

#### function,对象中定义的参数
- 传参需要显示指定参数名
- 要么required，要么指定默认值

void main(){
  shout(name:'xiaosong');
}

shout({required String name,address='196a st'}){
  print(name);
  print(address);
}

---

#### arrow function
> => xxx is just a syntaxic sugar to avoid { return xxx; }

- 箭头函数右侧是返回值
- 箭头函数不像ts可以有多行语句，如果涉及多行语句，可以直接用curly函数
- 箭头函数经常作为参数传递到另外一个函数里面 callIt(Function callback)

---

### arrow function 的几种定义方法

- 类似dart普通函数定义，只是箭头替换curly

void main(){
  Robot myRobot = Robot()
    ..age = 5;
    print(myRobot.calculate());
}

class Robot{
  late final int age;
  calculate()=> '$age years old';
}

- 完全匿名函数

void main(){
  myHandler(()=>'hello');
}

myHandler(Function callback){
  print(callback());
}

- 类似定义对象

void main(){
  myHandler(()=>'hello world!');
}

Function myHandler = (Function callback){
  print(callback());
};

---

### iterables
- List
- Map
- Set

---

#### List

> List inherits from Iterable


- List支持不同类型元素
- 定义时候加泛型，则只支持一种类型元素

___

##### List一些操作

List<int> myList = [1,4,5,9,12,15,19,20,22];
  
void main(){
  List<int> newList = myList.sublist(2,6);
  print('list length is ${newList.length}');
  //list length is 4
  print('the first item is ${newList[0]}');
  //the first item is 5
  print('the last item is ${newList[3]}');
  //the last item is 15
  print('the first item is ${myList.first}');
  //the first item is 5
  print('the first item is ${myList.last}');
  //the last item is 15
  
 var myList2 = List.filled(10,'g');
  print(myList2);
  //[g, g, g, g, g, g, g, g, g, g]
}

List<int> myList = [1,4,5];
  
void main(){
  List<int> myList = [1,4,5];
  myList.add(23);
  print(myList);
  //[1, 4, 5, 23]
  myList.removeLast();
  print(myList);
  [1, 4, 5]
}

List<int> myList = [1,4,5];
  
void main(){
  List<int> myList = [1,4,5];
  myList.add(23);
  print(myList);
  //[1, 4, 5, 23]
  myList.removeLast();
  print(myList);
  //[1, 4, 5]
  myList.insert(0,1000);
  print(myList);
  //[1000, 1, 4, 5]
}

___

##### forEach和map
> forEach无返回值，map返回一个新数组
- forEach(Function callback)
`list.forEach((n)=>print(n));`
- map(Function callback)
`var doubled = list.map((n)=>n*2);`

---

##### for...in

void main(){
  List<int> myList = [1,4,5];
  
  for(int i in myList){
    print('item is: $i');
  }
}

___

##### 类似js数组spread

  List<int> myList = [1,4,5];
  var newList = [99,...myList];
  var new2List = [...myList,99];
  print(newList);
  print(new2List);

  List<int> myList = [1,4,5];
  var newList = [99,...myList];
  var new2List = [...myList,99];
  print(newList);
  print(new2List);
  print([...newList,...new2List]);

___

##### 数组中逻辑判断

  bool isPublished = true;
  var students = [
    'a','b','c', if(isPublished) 'd'
  ];
  print(students);
  //[a, b, c]

  bool isPublished = true;
  int age = 43;
  var students = [
    'a','b','c', 50>age ? 'big': 'small'
  ];
  print(students);
  //[a, b, c, big]

___

#### Map

- Map本身可以forEach,不可以for(* in *)
- Map的keys，values, entries 可以 for(* in *),不可以forEach

##### Map一些操作

  Map<String,dynamic> book = {
    'name': 'vanvouver1978',
    'author': 'dylan',
    'publish': 1985,
    'isPublished': true
  };
  
  print(book.keys);
  print(book.values);
  print(book.values.toList()[0].runtimeType);
  print(book.entries);
  
  print(book['name']);
  print(book['author']);
  print(book['publish']);
  print(book['isPublished']);
  
  for(String bookKey in book.keys){
    print('book key is $bookKey');
  }
  
  for(dynamic bookValue in book.values){
    print('book value is $bookValue');
  }
  
  for (MapEntry b in book.entries) {
    print('Key ${b.key}, Value ${b.value}');
  }
  
  book.forEach((k, v) => print("Key : $k, Value : $v"));

___

#### class

##### 构造函数 初始化需要+this

void main(){ 
  var robot = Robot(32,'xiaosong');
  print(robot.age);
  print(robot.name);
}
class Robot {
  int age;
  String name;
  Robot(this.age,this.name);
}

___

##### 方法函数调用变量不需要+this

void main(){
  var robot = Robot(32,'xiaosong'); 
  robot.introduce();
  print(robot.age);
  print(robot.name);
}

class Robot {
  int age;
  String name;
  Robot(this.age,this.name);
  introduce(){
    print('my name is $name');
  }
}

___

##### 有些成员变量需要late

void main(){
 Rectangle rect = Rectangle(30,40);
 print('area ${rect.area}');
}
class Rectangle {
  int width;
  int height;
  late int area;
  Rectangle(this.width,this.height){
    this.area = this.width * this.height;
  }
}

___

##### 构造函数可选参数

void main(){
 Rectangle rect = Rectangle(30,40,'box');
 print('area ${rect.area}');
 print('rect name is ${rect.name}');
}
class Rectangle {
  int width;
  int height;
  late int area;
  String? name;
  Rectangle(this.width,this.height,[this.name]){
    this.area = this.width * this.height;
  }
}

___

##### 构造函数命名参数

void main(){
  Circle myCircle = Circle(rad:3,name:'myCircle');
  print(myCircle.rad);
}

class Circle {
    
   int rad;
  
   Circle({required this.rad, String? name});
}

> 构造函数前面加const，新建实例时候可以用const，注意成员需要final

void main(){
  const myCircle = Circle(rad:3,name:'myCircle');
  print(myCircle.rad);
}

class Circle {
   final int rad;
   const Circle({required this.rad, String? name});
}

---

##### 方法构造函数

void main(){
  Position myPosition = Position.fromMap({'x':321,'y':231});
  print(myPosition.x);
  
  Position myAnotherPosition = Position.fromList([321,231]);
  print(myAnotherPosition.y);
}

class Position {
  int x = 0;
  int y = 0;
  
  Position.fromMap(Map mapData){
    x = mapData['x'];
    y = mapData['y'];
  }
  
  Position.fromList(List listData){
    x = listData[0];
    y = listData[1];
  }
}

___

#### interface

class Elephant {
  // Public interface
  final String name;

  // In the interface, but visible only in this library. (private)
  final int _id = 23;

  // Not in the interface, since this is a constructor.
  Elephant(this.name);

  // Public method.
  sayHi() => 'My name is $name.';

  // Private method.
  _saySecret() => 'My ID is $_id.';
}

___

##### implements

void main(){
  const myPolice = Police('xiaosong',42);
  myPolice.introduce();
}


class Police implements Person{
  final int age;
  final String name;
  
  const Police(this.name,this.age):super();
  
  introduce(){
    print(name);
  }
}


abstract class Person {
  final int age;
  final String name;
  const Person(this.name,this.age);
  void introduce();
}

___

##### flutter中常见的extends

class GreenFrog extends StatelessWidget{
    const GreenFrog({Key? key}) : super(key:key);
    
    @override
    Widget build(BuildContext context){
        return Container(color: const Color(0xFF2DBD3A));
    }
}

___

##### 自己实现一个extends

  
void main(){
  const myPolice = Police('dylan',42,'manager');
  myPolice.introduce();
}



abstract class Person {
  final String name;
  final int age;
  const Person(this.name,this.age);
  void introduce(){
    print(name);
    print(age);
  }
}


class Police extends Person{
    final String name;
    final int age;
    final String title;
    const Police(this.name,this.age,this.title): super(name,age);
  
    @override
    void introduce(){
      super.introduce();
      print(title);
    }
}

___

##### 再实现一个

void main(){
  Police myPolice = Police(name:'dylan', age:42, title:'manager');
  myPolice.introduce();
}



abstract class Person {
  final String name;
  final int age;
  const Person(this.name,this.age);
  void introduce(){
    print(name);
    print(age);
  }
}


class Police extends Person{
    late final String name;
    late final int age;
    late final String title;
    Police({required name,required age,required title}): super(name,age){
      this.name = name;
      this.age = age;
      this.title = title;
    }
  
    @override
    void introduce(){
      super.introduce();
      print(title);
    }
}

___

##### 另外一种写法

  
void main(){
  Police myPolice = Police(name:'dylan', age:43, title:'manager');
  myPolice.introduce();
}



abstract class Person {
  final String name;
  final int age;
  const Person(this.name,this.age);
  void introduce(){
    print(name);
    print(age);
  }
}


class Police extends Person{
    late final String name;
    late final int age;
    late final String title;
    Police({required this.name,required this.age,required this.title}): super(name,age);
  
    @override
    void introduce(){
      super.introduce();
      print(title);
    }
}

___

##### 似乎这种写法更合理？

void main(){
  Police myPolice = Police('dylan', 44, title:'manager');
  myPolice.introduce();
}



abstract class Person {
  final String name;
  final int age;
  const Person(this.name,this.age);
  void introduce(){
    print(name);
    print(age);
  }
}


class Police extends Person{
    late final String name;
    late final int age;
    late final String title;
    Police(this.name,this.age,{required this.title}): super(name,age);
  
    @override
    void introduce(){
      super.introduce();
      print(title);
    }
}

___

#### mixin

- mixin写法类似于class,关键词换成mixin
- mixin没有构造函数
- mixin调用方法是with
- mixin可以通过get方法获取寄生类成员属性值

void main(){
  SuperMan mySuperMan = SuperMan('xiaosong',42);
  mySuperMan.sayFast();
  mySuperMan.sayStrong();
  mySuperMan.sayName();
}

class Human{
  String name;
  int age;
  Human(this.name,this.age);
  void sayName(){
    print('my name is $name');
  }
}

mixin Strong{
  int weight = 100;
  String get name;
  void sayStrong(){
    print('i am ${this.weight}');
    print('my name mixin is $name');
  }
}

mixin Fast{
  int speed = 120;
  void sayFast(){
    print('i am ${this.speed}');
  }
}

class SuperMan extends Human with Strong,Fast{
    String name;
    int age;
    SuperMan(this.name,this.age):super(name,age);
}

___

#### Generics

void main(){
  Box<String> myBox = Box('hello world');
  print(myBox.value);
  print('return value is ${myBox.openBox()}');
  
  Box<int> myBox2 = Box(32);
  print(myBox2.value);
  print('return value is ${myBox2.openBox()}');
  
  Box<double> myBox3 = Box(3.2);
  print(myBox3.value);
  print('return value is ${myBox3.openBox()}');
  
  Box<List<int>> myBox4 = Box([2,3,4,9,0]);
  print(myBox4.value);
  print('return value is ${myBox4.openBox()}');
}

class Box<T> {
  T value;
  Box(this.value);
  T openBox(){
    return value;
  }
}

___

##### Future

- 可以写成then的形式

void main(){
  Future delay = Future.delayed(Duration(seconds:5));
  delay.then((value)=>print('delayed')).catchError((e)=>print('erro!$e'));
}

- async函数定义在curly前

  Future<String> myFunc() async {
  ...
}

void main() async{
  MyFutureMessage myFutureMessage = MyFutureMessage('xiaosong');
  String message = await myFutureMessage.showMessage();
  print(message);
}

class MyFutureMessage {
  String name;
  MyFutureMessage(this.name);
  Future<String> showMessage() async {
    String result = await Future.value(name);
    return 'my name is $result';
  }
}

___

##### stream

- stream从`dart:async`中导入
- stream默认不是broadcast
- stream可以写到async中,以for in的形式

import 'dart:async';

void main() {
  Stream myStream = Stream.fromIterable([1,4,5,3,2,9,2]).asBroadcastStream();
  
  myStream.listen((v)=>print(v));
  
  myStream.map((v)=>v*3).listen((v)=>print('triple is $v'));
}

___

import 'dart:async';

void main() {
  
  
  void forInStream() async {
      Stream myStream = Stream.fromIterable([1,4,5,3,2,9,2]).asBroadcastStream();
    
      await for(int value in myStream) {
        print(value);
      }
  }
    
  forInStream();
 
}