Flutter Dart 기초문법 및 Iterable Class

Flutter & Dart 문법 좀 보면서 끄적끄적 정리해봅니다.

기초문법

Optional 매개변수 사용 2가지
positional Parameter – 항상 Default 값
getHttpUrl(String server, String path, [int port=80]) {}
named Parameter
– (String name, {int age})함수정의에서 {}로 감싸서 선택적으로 사용
named Parameter 쓸때는 무조건 함수호출할때 이름 넣어줘야한다.
2개 파라미터 같이 쓸수 없음.
익명함수
(number) {
return number % 2 === 0;
};
정적 Method
static int isValue(int param) {
}
문장 출력
– ”’ 멀티
용 ”’
변수타입 변경
변수타입이 후에 변경된다면 dynamic 사용
dynamic name = “이름”
List<dynamic> list = [1,2, “이름”];
Runtime시 오브젝트 type 확인
object.runtimeType returns the type of object
final aListOfStrings = [‘one’, ‘two’, ‘three’] – JSArray<String>
final aSetOfStrings = {‘one’, ‘two’, ‘three’} – _LinkedHashSet<String> [add/remove/contains]
final aMapOfStringsToInts = { ‘one’: 1, ‘two’: 2, ‘three’: 3,} – JsLinkedHashMap<String, int>
스프레드연산 (…)
list 내역들을 뿌려주는 역할
var numbering = [1,2,3]
[…numbering, 4,5]
Cascades 사용 (계단식)
myObject
..someMethod()
Class 접근 지정자
변수이름 앞에 _ 기호를 붙이면 외부에서 접근불가, 안붙이면 외부에서 접근가능
get / set

class MyClass {
int _aProperty = 0;
int get aProperty => _aProperty;
set aProperty(int value) {
if (value >= 0) {
_aProperty = value;
}
}
}

null 확인 ?.

dart:core library (link)

Iterable 정리

Iterable Class는 List, Set 가 있고 시퀀스하게 접근가능

final aListOfStrings = ['one', 'two', 'three'];
final aSetOfStrings = {'one', 'two', 'three'};
final aMapOfStringsToInts = {
  'one': 1,
  'two': 2,
  'three': 3,
};
아래처럼 지정해도됨.
final aListOfInts = <int>[];
final aSetOfInts = <int>{};
final aMapOfIntToDouble = <int, double>{};

– Iterable<int> iterable = [1, 2, 3];
iterable.elementAt(1); iterable.first; iterable.last;

: Using any() and every()
iterable.firstWhere(); 식표현 사용방법 3가지

bool predicate(String element) {
  return element.length > 5;
}

main() {
  var items = ['Salad', 'Popcorn', 'Toast', 'Lasagne'];

  // You can find with a simple expression:
  var element1 = items.firstWhere((element) => element.length > 5);
  print(element1);

  // Or try using a function block:
  var element2 = items.firstWhere((element) {
    return element.length > 5;
  });
  print(element2);

  // Or even pass in a function reference:
  var element3 = items.firstWhere(predicate);
  print(element3);

  // You can also use an `orElse` function in case no value is found!
  var element4 = items.firstWhere(
    (element) => element.length > 10,
    orElse: () => 'None!',
  );
  print(element4);
}

As an expression : 람다식
As a block: 함수에 return식
As a function : 안에 orElse 추가

Example: Using any() and every()

any(): 하나의 element를 만족하면 Return true
every(): 모두 만족하면 Return true
if (items.any((element) => element.contains(‘Z’))) { }

Filtering Example: Using where()
singleWhere() or firstWhere(), where() 값 만족 못하면 empty값 들어옴.

Filtering Example: Using takeWhile
takeWhile(): 조건 만족전까지만 출력 (until)
skipWhile() : 조건 만족한거부터 출력 (after)

Mapping

PUB 라이브러리

pub get (link) : 외부 라이브러리를 추가한후 다운
pub upgrade (link) : 외부라이브러리 업그레이드
pub outdated (link): 2.8 이후 추가 최신 다운
그밖에 리스트 (link)
CLI : – $ flutter / dart + pub outdated [options]

pub get 에서 받는거 쌓이는 디렉토리 /.pub-cache. 윈도우 %LOCALAPPDATA%\Pub\Cache

패캐지 사이트

https://pub.dev/

테스트 실행환경

https://dartpad.dev/?

Sample Code

기본 구조는 다음에 올려야겠다..

import 'package:flutter/material.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        // This is the theme of your application.
        //
        // Try running your application with "flutter run". You'll see the
        // application has a blue toolbar. Then, without quitting the app, try
        // changing the primarySwatch below to Colors.green and then invoke
        // "hot reload" (press "r" in the console where you ran "flutter run",
        // or simply save your changes to "hot reload" in a Flutter IDE).
        // Notice that the counter didn't reset back to zero; the application
        // is not restarted.
        primarySwatch: Colors.blue,
        // This makes the visual density adapt to the platform that you run
        // the app on. For desktop platforms, the controls will be smaller and
        // closer together (more dense) than on mobile platforms.
        visualDensity: VisualDensity.adaptivePlatformDensity,
      ),
      home: MyHomePage(title: 'Flutter TEST Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  // This widget is the home page of your application. It is stateful, meaning
  // that it has a State object (defined below) that contains fields that affect
  // how it looks.

  // This class is the configuration for the state. It holds the values (in this
  // case the title) provided by the parent (in this case the App widget) and
  // used by the build method of the State. Fields in a Widget subclass are
  // always marked "final".

  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  int _counter = 0;

  void _incrementCounter() {
    setState(() {
      // This call to setState tells the Flutter framework that something has
      // changed in this State, which causes it to rerun the build method below
      // so that the display can reflect the updated values. If we changed
      // _counter without calling setState(), then the build method would not be
      // called again, and so nothing would appear to happen.
      _counter++;
    });
  }

  @override
  Widget build(BuildContext context) {
    // This method is rerun every time setState is called, for instance as done
    // by the _incrementCounter method above.
    //
    // The Flutter framework has been optimized to make rerunning build methods
    // fast, so that you can just rebuild anything that needs updating rather
    // than having to individually change instances of widgets.
    return Scaffold(
      appBar: AppBar(
        // Here we take the value from the MyHomePage object that was created by
        // the App.build method, and use it to set our appbar title.
        title: Text(widget.title),
      ),
      body: Center(
        // Center is a layout widget. It takes a single child and positions it
        // in the middle of the parent.
        child: Column(
          // Column is also a layout widget. It takes a list of children and
          // arranges them vertically. By default, it sizes itself to fit its
          // children horizontally, and tries to be as tall as its parent.
          //
          // Invoke "debug painting" (press "p" in the console, choose the
          // "Toggle Debug Paint" action from the Flutter Inspector in Android
          // Studio, or the "Toggle Debug Paint" command in Visual Studio Code)
          // to see the wireframe for each widget.
          //
          // Column has various properties to control how it sizes itself and
          // how it positions its children. Here we use mainAxisAlignment to
          // center the children vertically; the main axis here is the vertical
          // axis because Columns are vertical (the cross axis would be
          // horizontal).
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text(
              'You have pushed the button this many times:',
            ),
            Text(
              '$_counter',
              style: Theme.of(context).textTheme.headline4,
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: _incrementCounter,
        tooltip: 'Increment',
        child: Icon(Icons.add),
      ), // This trailing comma makes auto-formatting nicer for build methods.
    );
  }
}