Dart语法要点汇总

// main为Dart程序入口
void main() {
  // 调用printNumber方法
  var number = 58;
  printNumber(number);
}

// 方法返回类型缺省时，默认返回类型为dynamic
printNumber(int number) {
  // 1. 字符串用单/双引号均可
  // 2. 字符串中支持${}表达式, 单字符变量时可简化为$
  print("The number is $number.");
}

The number is 58.

var name = 'Bob';

dynamic name = 'Bob';

String name = 'Bob';

int lineCount;
assert(lineCount == null);

final String nickname = 'Jack';
// final修饰时, 可省略类型声明
final name = 'Jack';

// 此时不能在对列表a进行更新操作
var a = const [1, 2];

// String -> int
var a = int.parse('1');
assert(a == 1);

// String -> double
var b = double.parse('1.1');
assert(b == 1.1);

// int -> String
String c = 1.toString();
assert(c == '1');

// double -> String
String d = 3.14159.toStringAsFixed(2);
assert(d == '3.14');

void main() {
  // 初始化
  var list = ['a', 'b', 'c'];
  // 增
  list.add('d');
  // 删
  list.remove('b');
  // 改
  list[1] = 'cc';
  // 查
  var last = list[list.length - 1];
  print('list is $list');
  print('last is $last');
}

list is [a, cc, d]
last is d

void main() {
  var map = {'a': 1, 'b': 2};
  // 增
  map['c'] = 3;
  // 删
  map.remove('a');
  // 改
  map['b'] = 22;
  // 查
  var cValue = map['c'];
  print('map is $map');
  print('cValue is $cValue');
}

map is {b: 22, c: 3}
cValue is 3

void say() {
    print('123');
}

// 该写法与以上有同样效果
void say2() => print('123');

void main() {
  say(age: 27);
}

void say({String name='Jack', int age=20}) {
  print('$name\'s age is $age.');
}

Jack's age is 27.

void main() {
  say('Tom', 27, 'Love game.');
}

void say(String name, int age, [String remark]) {
  print('$name\'s age is $age.${remark??''}');
}

Tom's age is 27.Love game.

void main() {
  var list = ['Android', 'iOS', 'WindowPhone'];
  list.forEach((item) {
    print(item);
  });
}

Android
iOS
WindowPhone

// 抛异常
throw FormatException('Expected at least 1 section');
throw 'Out of llamas!';

// 捕获异常
try {
  breedMoreLlamas();
} on OutOfLlamasException {
  // A specific exception
  buyMoreLlamas();
} on Exception catch (e) {
  // Anything else that is an exception
  print('Unknown exception: $e');
} catch (e) {
  // No specified type, handles all
  print('Something really unknown: $e');
}

try {
  // ···
} on Exception catch (e) {
  print('Exception details:\n $e');
} catch (e, s) {
  print('Exception details:\n $e');
  // 第二个参数s是一个错误堆栈实例
  print('Stack trace:\n $s');
}

try {
  dynamic foo = true;
  print(foo++); // Runtime error
} catch (e) {
  print('misbehave() partially handled ${e.runtimeType}.');
  // 关键字rethrow重新抛出异常
  rethrow; // Allow callers to see the exception. 
}

class Vector {
  final int x, y;

  Vector(this.x, this.y);

  Vector operator +(Vector v) => Vector(x + v.x, y + v.y);
  Vector operator -(Vector v) => Vector(x - v.x, y - v.y);

  // Operator == and hashCode not shown. For details, see note below.
  // ···
}

void main() {
  final v = Vector(2, 3);
  final w = Vector(2, 2);

  assert(v + w == Vector(4, 5));
  assert(v - w == Vector(0, 1));
}

Iterable<int> naturalsTo(int n) sync* {
  int k = 0;
  while (k < n) yield k++;
}

Stream<int> asynchronousNaturalsTo(int n) async* {
  int k = 0;
  while (k < n) yield k++;
}

Iterable<int> naturalsDownFrom(int n) sync* {
  if (n > 0) {
    yield n;
    yield* naturalsDownFrom(n - 1);
  }
}

class WannabeFunction {
  call(String a, String b, String c) => '$a $b $c!';
}

main() {
  var wf = new WannabeFunction();
  var out = wf("Hi","there,","gang");
  print('$out');
}