Dart语言快速学习上手（新手上路）

Dart语言快速学习上手（新手上路）

// 声明返回值
int add(int a, int b) {
  return a + b;
}

// 不声明返回值
add2(int a, int b) {
  return a + b;
}

// =>是return语句的简写
add3(a, b) => a + b; 

//命名参数、位置参数、参数默认值

sayHello({String name}) {
  print("hello, my name is $name");
}

sayHello2({name: String}) {
  print("hello, my name is $name");
}

//位置参数
sayHello(String name, int age, [String hobby]) { // 位置参数可以有多个，比如[String a, int b]
  StringBuffer sb = new StringBuffer();
  sb.write("hello, this is $name and I am $age years old");
  if (hobby != null) {
    sb.write(", my hobby is $hobby");
  }
  print(sb.toString());
}



// 命名参数的默认值
int add({int a, int b = 3}) { // 不能写成：int add({a: int, b: int = 3})
  return a + b;
}

// 位置参数的默认值
int sum(int a, int b, [int c = 3]) {
  return a + b + c;
}


//函数作为一类对象

printNum(int a) {
  print("$a");
}

//将一个函数赋值给某个变量
printNum(int a) {
  print("$a");
}

//匿名函数

test(Function callback) {
  callback("hello");
}

//


void main() {
  
  print("hello world!");

  var a = 1;
  int b = 10;
  String s = "hello";
  dynamic c = 0.5;

  var count = 10; 
  final Num = count;  // final 只能赋值一次
  const Num1 = 10; // const赋值必须是编译时常量

  // numbers
  var a = 0;
  int b = 1;
  double c = 0.1;

  // strings
  var s1 = 'hello';
  String s2 = "world";

  // booleans
  var real = true;
  bool isReal = false;

  // lists
  var arr = [1, 2, 3, 4, 5];
  List<String> arr2 = ['hello', 'world', "123", "456"];
  List<dynamic> arr3 = [1, true, 'haha', 1.0];

  // maps
  var map = new Map();
  map['name'] = 'zhangsan';
  map['age'] = 10;
  Map m = new Map();
  m['a'] = 'a';

  //runes，Dart 中 使用runes 来获取UTF-32字符集的字符。String的 codeUnitAt and codeUnit属性可以获取UTF-16字符集的字符
  var clapping = 'u{1f44f}';
  print(clapping); // 打印的是拍手emoji的表情

  // symbols
  print(#s == new Symbol("s")); // true

  print(add(1, 2)); // 3
  print(add2(2, 3)); // 5
  print(add3(1, 2)); // 3


  // hello, this is zhangsan and I am 20 years old
  sayHello("zhangsan", 20);
  // hello, this is zhangsan and I am 20 years old, my hobby is play football
  sayHello("zhangsan", 20, "play football");

  //  依次打印：
  //  1
  //  2
  //  3
  var arr = [1, 2, 3];
  arr.forEach(printNum);


  var f1 = printNum;
  Function f2 = printNum;
  var f3 = (int a) => print("a = $a");
  f1(1);
  f2(2);
  f3(6);


  test((param) {
    // 打印hello
    print(param);
  });

}