dart2练习

basic.dart

// 程序以main开始
// 结尾有分号
// 字符串拼接${}表达式
void main() {
  for (int i = 0; i < 5; i++) {
    printTest('hello ${i + 1}');
  }
}

void printTest(String variableInteger) {
  print(variableInteger);
}

Built-inTypes.dart

// numbers
// strings
// booleans
// lists (also known as arrays)
// maps
// runes (for expressing Unicode characters in a string)
// symbols
void main() {
  // numbers
	int i = 1;
  double d = 1.1;
  
	final p1 = "3";
  final p2 = "3.3";
  print(int.parse(p1));
  print(double.parse(p2));
  
  // string
  final str1 = "test";
  final str2 = "test";
  print(str1 == str2);
  
  final str3 = 'test';
  print(str3);
  
  final str4 = '''test''';
  print(str4);
  print(str4 == str3);
  
  print("I'm ${str4}!!!");
  
  //booleans
  if(null) {
    print('null is true');
  } else {
    print('null is false');
  }
  
  print(''.isEmpty);
//   final list = [];
//   if(!list) {
//     print('not empty');
//   }
  
}

constructors1.dart

class Person {
  String name;
  int age;
  String dantengt;
 
  // 注意，冒号后边是初始化列表，用，隔开。
  Person() :dantengt = "danm";
  
  @override
  String toString() => "name : ${name};age : ${age}";
}

class Person2 {
  String name;
  int age;
  String danteng;
  
  // 关于构造器比较复杂，参考 https://www.dartlang.org/guides/language/language-tour#constructors
  // 默认构造器只能声明一个
  Person2(this.name,this.age);
  
  // 命名构造器
  Person2.copy(Person p) {
    this.name  = p.name;
    this.age = p.age;
  }
  
  @override
  String toString() => "name : ${name};age : ${age}";
}

class Student extends Person2 {
  final String school;
  // 普通构造器继承
  Student(String name,int age,this.school):super(name,age);
  // 命名构造器的继承
  Student.copy(Person p,this.school):super.copy(p);
	// 类似构造器的重载
  Student.mySchoolCopy(Person p):this.copy(p,'mySchool');
}

class ImmutablePoint {
  static final ImmutablePoint origin =
      const ImmutablePoint(0, 0);

  final num x, y;
	// cosnt修饰的构造器是常量构造器，里面的值都不许改变。因为是编译时的。
  const ImmutablePoint(this.x, this.y);
}

void main() {
  final person = Person();
  person.name = "spawn";
  person.age = 18;
  print(person);
  
  final person2 = Person2("lecon",25);
  print(person2);
  print(Person2.copy(person));
  
  Person2 p2 = Student("lecon",25,"haha");
  
  // is 和 as ;类似 instanceof和强转
  if (p2 is Student) {
    (p2 as Student).school;
  }
}

constructors2.dart

class Person2 {
  String name;
  int age;
  
  Person2(this.name,this.age);
  
  // factory 构造器也是构造器，同样不能声明两个相同名字的，而且只能有一个默认
  // factory 没有this引用
  factory Person2.select(name,int age,int type) {
    if(type == 0) {
      return Student(name,age,"jaja");
    } else {
      return Worker(name,age,"lala");
    }
  }
  // callable
  call(String a, String b, String c) => '$a $b $c!';
  
  @override
  String toString() => "name : ${name};age : ${age}";
}

class Student extends Person2 {
  final String school;
  
  Student(String name,int age,this.school):super(name,age);
}

class Worker extends Person2 {
  final String company;
  
  Worker(String name,int age,this.company):super(name,age);
}

void main() { 
	// 不关注Person2实现类，直接使用Person2实例化。使用factory
	final p1 = Person2.select("lecon",23,0);
  final p2 = Person2.select("lecon",23,1);
  print(p1.runtimeType);
  print(p2.runtimeType);
  // callable
  print(p1("123","234","345"));

}

default.dart

// 所有类型的默认值都是null
void main() {
	int i;
  String str1;
  print(i);
  print(str1);
}

Exceptions.dart

void main() {
// 	throw1();
//   	throw2();
//   throw3();
//     throw4();
      throw5();
}

void throw1() {
  throw FormatException('Expected at least 1 section');
}

void throw2() {
  throw 'Expected at least 1 section';
}

void throw3() {
  try {
    throw FormatException('Expected at least 1 section');
  } on FormatException {
    print('section exception');
  }
  try {
    throw FormatException('Expected at least 1 section');
  } on FormatException catch(e) {
     print('section exception ${e}');
  }
  try {
    throw FormatException('Expected at least 1 section');
  } on FormatException catch(e,s) {
    print('section exception ${e}');
    print(s); // 打印方法调用栈
  }
}

void throw4() {
  try {
    throw FormatException('Expected at least 1 section');
  } on FormatException {
    print('section exception');
    rethrow; // 重抛
  }
}

void throw5() {
   try {
    throw FormatException('Expected at least 1 section');
  } on FormatException {
    print('section exception');
  } finally {
     print("I am finally");
  }
}

funciton.dart

// import 'package:meta/meta.dart'

void main() {
 func1(123);
 func2('222');
  func3("lecon");
//   func3("lecon","spawn",123); error,使用下边的中括号，注意区别。这个使用key区分，下面使用位置区分
  func3("lecon",param2:"spawn",param3:123);
//   func4("lecon",param2:"spawn"); error required 
  func5("lecon","spawn","hahaa");
  func6("lecon",age:25);
  print(func7());
}

void func1(param1) {
  print(param1);
}
void func2(String param2) {
  print(param2);
}

void func3(String param1,{String param2,int param3}) {
  print("I am ${param1}, Hi ${param2},I am ${param3}");
}

// test in flutter
// void func4(String param1,{String param2,@required int param3}) {
//   print("I am ${param1}, Hi ${param2},I am ${param3}");
// }


void func5(String param1,[String param2,String param3]) {
  print("I am ${param1}, bian bu ${param2} xia qu le ${param3}");
}

// 只有使用{}和[]的才可以有默认值
void func6(String param1,{int age = 23}) {
  print("I am ${param1}, I am ${age}");
}

func7() {
  void func8() {
    
	}
  
  void func9() {
    
  }
  
  retrun () => "123";
}

123
222
I am lecon, Hi null,I am null
I am lecon, Hi spawn,I am 123
I am lecon, bian bu spawn xia qu le hahaa
I am lecon, I am 25
null

Generators.dart

// 同步异步 https://www.dartlang.org/guides/libraries/library-tour#future
void main() {
	print(naturalsTo(10));
  print(naturalsDownFrom(10));
  asynchronousNaturalsTo(10)
    .toList()
    .then((res) {
      print(res);
    });
}

// 同步生成器
Iterable<int> naturalsTo(int n) sync* {
  int k = 0;
  while (k < n) yield k++;
}

// 异步生成器
Stream<int> asynchronousNaturalsTo(int n) async* {
  int k = 0;
  while (k < n) yield k++;
}

// 递归性质的生成器
Iterable<int> naturalsDownFrom(int n) sync* {
  if (n > 0) {
    yield n;
    yield* naturalsDownFrom(n - 1);
  }
}

import.dart

import 'package:lib1/lib1.dart';
import 'package:lib2/lib2.dart' as lib2;
// 仅导入foo
import 'package:lib1/lib1.dart' show foo;
// 排除foo
import 'package:lib2/lib2.dart' hide foo;
// 异步导入
import 'package:greetings/hello.dart' deferred as hello;

list.dart

// https://api.dartlang.org/stable/2.1.0/dart-core/List-class.html
void main() {
  // 初始化
  final list1 = [1,2,3,4,5];
  // 编译时常量
  final list2 = const [2,3,4,5,6];
//   list2[2] = 8; error
  print(list2);
  
  // 初始化2
  List<int> list3 = new List(5);
  print(list3);
  
  // 初始化3
  List<int> list4 = List.filled(3,10);
  print(list4);
  
  // 初始化4
  List<int> list5 = List.generate(3,(i) => i * 3);
  print(list5);
  
  // 更改 使用list1
  list1[2] = 8;
  print(list1);
  // 添加
  list1.add(10);
//   list1[10] = 20; Index out of range
  print(list1);
  //删除
  list1.remove(10);
  print(list1);
}


[2, 3, 4, 5, 6]
[null, null, null, null, null]
[10, 10, 10]
[0, 3, 6]
[1, 2, 8, 4, 5]
[1, 2, 8, 4, 5, 10]
[1, 2, 8, 4, 5]

Maps.dart

import 'dart:convert';
// https://api.dartlang.org/stable/2.1.0/dart-core/Map-class.html
void main() {
	final map1 = {
    "test1key" : "test1value",
//     "test1key" : "test1value", Key 不能相同
    123 : "123value",
    null : 'NULL',
    2 : '2'
  };
  print(map1);
  // 获取值
  print(map1[123]); // key取值
  print(map1[1]); // 下标取值
  print(map1[2]); // 同时存在时候，优先Key取值
  // 追加值
  map1['appendKey']  = 'appendVal';
  print(map1);
  // 更改值
  map1['appendKey']  = 'appendVal123';
  print(map1);
 	map1['appendKey'] = null;
  print(map1); // 置位null之后，key不会消失
  map1.remove('appendKey');
  // 删除
  print(map1); 
  
  print(map1['non-key']); // null 不会报错
  print(map1.length); // 长度
  
  // json 转换
  final map2 = const {
    "name":"lecon",
    "age":23,
    "ss":[1,2,3,4,4]
  };
  final jsonText = jsonEncode(map2);
  print(jsonText);
  final mapObj = jsonDecode(jsonText);
  print(mapObj);
}



{test1key: test1value, 123: 123value, null: NULL, 2: 2}
123value
null
2
{test1key: test1value, 123: 123value, null: NULL, 2: 2, appendKey: appendVal}
{test1key: test1value, 123: 123value, null: NULL, 2: 2, appendKey: appendVal123}
{test1key: test1value, 123: 123value, null: NULL, 2: 2, appendKey: null}
{test1key: test1value, 123: 123value, null: NULL, 2: 2}
null
4
{"name":"lecon","age":23,"ss":[1,2,3,4,4]}
{name: lecon, age: 23, ss: [1, 2, 3, 4, 4]}

mixins.dart

mixin Play {
  void play() {
    print("I can play");
  }
}

mixin Eat {
  void eat() {
    print("I can eat");
  }
}

class Person with Play,Eat {
  final String name;
  final int age;
  Person(this.name,this.age);
}

void main() {
  final p = Person("lecon",13);
  p.play();
  p.eat();
}

Runes.dart

main() {
  var clapping = '\u{1f44f}';
  print(clapping);
  print(clapping.codeUnits);
  print(clapping.runes.toList());

  Runes input = new Runes(
      '\u2665  \u{1f605}  \u{1f60e}  \u{1f47b}  \u{1f596}  \u{1f44d}');
  print(new String.fromCharCodes(input));
}

setter_getter.dart

class Rectangle {
  num left, top, width, height;

  Rectangle(this.left, this.top, this.width, this.height);

  num get right => left + width;
  set right(num value) => left = value - width;
  num get bottom => top + height;
  set bottom(num value) => top = value - height;
}

void main() {
  var rect = Rectangle(3, 4, 20, 15);
  assert(rect.left == 3);
  rect.right = 12;
  assert(rect.left == -8);
}

variables.dart

void main() {
  int l = 4;
  String str1 = "str1";
	var i = 1;
  final j = 2;
  const k = 3;
}