[又重學flutter]Dart資料格式

 Dart的資料格式

可在此網址測試

https://dartpad.dev/?null_safety=true

void main() {
  var number = 1;
  var bool = number is int; //String //double
  print(bool); // true
  dynamic numberOrString = 1;
  numberOrString = '1';
  //--------------------------------------------//
  List<dynamic> list = [1, '1', true];
  print(list);
  list.forEach((item) => print(item)); //參數括弧不可拿掉（不同於js）
  for(var item in list) print(item);
  list.add('a');
  print(list); //[1, 1, true, a]
  List<dynamic> list2 = [2];
  list2.addAll(list);
  print(list2); //[2, 1, 1, true, a]
  list2.clear();
  print(list2); // []
  print(list.indexOf('a')); //3
  print(list.map((e) => 5).toList()); //[5, 5, 5, 5] //toList是為了讓iterable變成list
  //--------------------------------------------//
  var map = {
    'key': 'value',
    'key2': 'value2'
  };
  print(map['key']); //value
  print(map['willBeNull']); //null
  print(map.length); //2
  print(map.containsKey('key')); //true
  print(map.entries); //(MapEntry(key: value), MapEntry(key2: value2))
  print(map.values); //(value, value2)
  print(map.keys); //(key, key2)
  print(map.values.toList()); //[value, value2]
  print(map.keys.toList()); //[key, key2]
  Map<String, String> map2 = {
    "a": "2"
  };
  map2.addAll(map);
  print(map2); //{a: 2, key: value, key2: value2}
  print(map2.containsValue('value')); //ture
  Map<String, String> map3 = map2.map((key,value) => MapEntry(key, '${value}5566'));
  print(map3); // {a: 25566, key: value5566, key2: value25566}
  map3.putIfAbsent('b', () => '7788');
  print(map3); //{a: 25566, key: value5566, key2: value25566, b: 7788}
  map3.removeWhere((key, value) => key == 'b');
  print(map3); //{a: 25566, key: value5566, key2: value25566}
  //--------------------------------------------//
  String fun(int number) {
    return "${number}";
  }
  print(fun(number)); //1
  String fun2(int number) => "${number}";
  print(fun2(number)); //1
  String fun3({ int number=3 }) => "${number}";
  print(fun3()); //3 (括弧內參數可有可無)
  print(fun3(number: 4)); //4 (若要傳入就要指定)
  try {
    throw new IntegerDivisionByZeroException();
  }catch(e) {
    print(e);
  }finally {
    print('wil be here whether success or fail');
  }
  //--------------------------------------------//
  var person = Person(h: 177, n: "Jerry");
  print(person.height); //177
  var person2 = Person.defaultPerson();
  print(person2.height); //100
  person2.setHeight(200);
  print(person2.getHeight()); //200
  var badPerson = BadPerson();
  print(badPerson.height); //0
  var goodPerson = GoodPerson(h2: 999, n2: "Sony");
  print(goodPerson.height); //999
  print(identical(badPerson, goodPerson)); //false
}
class Person {
  int height = 0;
  String name = "someone";
  final country = "taiwan";
  Person({ int h: 0, String n: 'someone' } ) {
    assert(h == 177, 'not good'); //若在手機跑就會停在這裡
    this.height = h;
    this.name = n;
  }
  //等同於以下code
  //Person(this.height, this.name) : assert(height ==177, 'not good');
  //若要接下一個assert就用逗號隔開
  Person.defaultPerson(){} //不用分號
  int getHeight() => this.height;
  void setHeight(int h) => this.height = h;
  // void setCountry(String c) => this.country = c;(不能這樣寫，因為是final)
}

class BadPerson extends Person {
  
}
class GoodPerson extends Person {
  GoodPerson({ int h2: 180, String n2: 'GoodMan' }) : super(h: h2, n: n2);
  //super等於Person //同Person(h: 177, n: "Jerry");
  //小孩的傳參放入爸爸的傳參
}